US3019438A - Antenna structure - Google Patents

Description

Jan. 30, 1962 P. M. PAN

ANTENNA STRUCTURE 4 Sheets-Sheet 1 Filed March 18, 1957 Video Energy u u A nergy Aural Antenna 42 Video Energy Probe Circular Waveguide INVENTOR PAUL M. PAN

////////////////////////l/lll/lIll/Ill Jan. 30, 1962 P. M. PAN 3,019,438

ANTENNA STRUCTURE Filed March 18, 1957 4 Sheets-Sheet 2 Transducer 24 Transducorfi //VVEN7'OR PAUL M. PA N 8V V Choke shodgg Jan. 30, 1962 P. M. PAN 3,019,438

ANTENNA STRUCTURE Filed March 18, 1957 4 Sheets-Sheet 3 FIG. [4

A m/x Ann/m mXm nn UWUUWUTV FIG/2 INVENTOR. PAUL M. PAN

BY W W ATTORNEY Jan. 30, 1962 P. M. PAN 3,019,438

ANTENNA STRUCTURE Ground Plane 0 1 2 I87 Duol Signal Cross Polorizorion System 2 3( i HYBRID TRANSMITTER JUNCTION SYSTEM ANTENNA SWITCH SELECT CIRCUIT SWITGH 2'2 HYBRID F ED I I ZJE JUNCTION WI A Z Z Z 224 CIRCUIT Antenna Sysrem|9 0 FIG. I6

Single Signal Selective Polarization System2 2 Q FIG. /7

INVENTOR. PAUL M. PAN

ATTORNEY iinite States i atent 3,019,438 Fatented Jan. 30, 1962 3,919,438 ANTENNA STRUiZTURE Paul M. Pan, North Syracuse, N.Y., assignor to General Electric Company, a corporation of N cw York Filed Mar. 18, 1957, Ser. No. 646,837 30 Claims. (G. 343-843} This invention relates to antenna structures of the kind used for radiation and reception of electromagnetic energy, and more particularly to antenna systems for radiating or receiving radio frequency energy which may carry different information or radio frequency energy which may be polarized in different directions.

The need to radiate radio frequency energy which conveys separate information is illustrated by television broadcasting. In broadcasting television programs to television receivers in a surrounding area it is of great importance for proper reception that both the picture signal and the sound signal, which are generated by separate transmitters, be received at about the same strength. One solution was to mount both the picture and sound transmitting antennas on a high tower or high building. However, it was found that due to the close proximity of the sound and picture antennas energy would be coupled between the antennas and therefore from one transmitter to the other transmitter to interfere with the operation of the system.

Since it was not practical to separate the picture and sound antennas, a radiation system was developed which permitted mounting of the picture and sound antenna systems on the same mast by using complex filter equipment to prevent the transfer of energy between the transmitters. The improved results achieved by the use of the filter equipment created a demand for an even better system because, in addition to being expensive, the filter opportunity to view television. In addition, the filter equipment reduced the bandwidth of the radiating system; that is, the system would be limited to operating in a relatively narrow frequency range which in some cases would impair the quality of the broadcast.

Therefore, an object of the invention is to provide an improved antenna system for broadcasting the picture and sound signals of a television station.

A more general object of the invention is to provide an improved antenna system.

Another object of this invention is to provide an improved antenna system for radiating more than one signal from the same location.

Another object of the invention is to provide an improved antenna system for radiating two forms of information in a uniform radiation pattern in azimuth and a narrow radiation pattern in elevation and which operates over a relatively broad band of frequencies.

A similar problem exists in the communication industry with respect to transmitting different frequency signals from the same antenna structure (diplexing) or transmitting and receiving different signals at the same time using the same antenna structure (duplexing).

In the case of multi-signal communication systems where different signals may be transmitted to different receiving systems at the same time, it has been the usual practice to provide a separate antenna for each transmitter. This, of course, was expensive particularly since separate masts were sometimes required. If each antenna were also used for receiving as well as transmitting, it was important that transmission at one frequency would not interfere with local reception at another frequency and the need for separate antenna systems spaced as far apart the radiated energy at as possible Was even more necessary. One partial solution was to employ expensive and complicated filter equipment to prevent interference between the stations.

Therefore, another object of this invention is to provide an improved antenna system for transmitting or receiving two signals simultaneously which may be mounted on the same support structure in close proximity without causing undue interference.

Another more general object of the invention is to provide an improved multi-signal antenna system.

Another situation that often exists in communication systems is the problem of communicating with receiving locations which have antenna systems which may be polarized in different ways. For example, a whip antenna on a mobile station installation such as an automobile is usually vertical and therefore the best reception from a transmitting station occurs for signals which are radiated from antennas which are vertically polarized. However, the same transmitting station may also be required to transmit to receiving installations which have antenna systems which are horizontally or circularly polarized. The problem is two-fold since both stations usually transmit and receive. In the past, many installations used a number of antennas arranged to provide different polarizations or simply operated with less efficiency using different polarization at the transmitting and the receiving locations.

A similar problem exists in the radar industry where there is a need to be able to change the polarization of will. For example, changing the polarization from linear to circular is used in many radar applications Where the effects of rain are to be minimized.

Therefore, another object of the invention is to provide an improved antenna system for radiating energy at a selected polarization.

Still another object of this invention is to provide an improved antenna system which may transmit and receive signals With different polarization, yet which is compact and readily supportable on the same structure.

A general object of the invention is to provide an improved antenna system which is relatively simple to construct, easy to install, rugged, and effective in operation.

Briefly, the invention is embodied in apparatus comprising two helical antennas and antenna support means. The two helical antennas are supported by the antenna support means so that they have a common axis. Separate feeding means are provided to feed signals to the helical antennas. The two helical antennas may have the same or different diameters, may wind in the same or opposite directions, or may be interlaced or cross-wound.-

There is very little coupling between the two helical antennas so that no substantial amount of interference occurs.

In accordance with one embodiment of the invention, which is particularly suitable for broadcasting two signals such as the aural (sound) and video (picture) signals in television broadcasting, the antenna support means is a mast and the two helical antennas wind around the mast but are insulated from the mast. In this case the radiation is side fire; that is, the radiation is horizontally polarized and normal to the axis of the helical antennas.

An advantage of this embodiment of the invention is that the mast may also function as a wave guide to feed Another advantage of this embodiment of the invention is that the antenna system may readily be arranged verti cally in a number of bays to increase the area of broadcasting by concentrating the radiation in the radial direction.

In accordance with another embodiment of the invention particularly useful in communications for diplexing or duplexing, the two helical antennas are supported at their ends by antenna support means such as a ground plane and the polarization is circular.

In accordance with still another embodiment of the invention (which is especially valuable in radar and communications applications), the two helical antennas are supported in superimposed relation by antenna support means such as a ground plane and are wound in opposite directions so that turns of the two helical antennas cross. The same signal is fed via phasing devices leading to the two helical antennas. The radiation is axial or end fire. By controlling the phasing the polarization of the transmitted signal may be selected to be circular in either of two directions or may be selected to be vertical in either of two directions. Further, two separate transmitters may be used with this embodiment of the invention and their signals simultaneously radiated with different polarizations.

Other advantages, and additional objects and features of the invention will become apparent from the following detailed description which is accompanied by drawings in which:

FIGURES 1 to 10 illustrate a complete energy transfer system in accordance with one embodiment of the inven- 9 tion which employs side fire radiation and is particularly suitable for television broadcasting. The energy transfer system includes a mast which functions as a wave guide feeding system for coupling aural and video energy in orthogonal modes to the two helical antennas (in partial overlap) which function as the aural antenna and video antenna respectively;

FIGURE 1 shows a radiation system in accordance with a two-bay embodiment of the invention in which the aural and video energy is propagated in orthogonal modes within the circular wave guide mast by a transducer, and the aural and video energy is radiated by separate helical antennas which are cross-wound to reduce coupling,

FIGURE 2 is a more detailed view of the top bay of the radiation system of FIGURE 1 illustrating the two helical antennas and the positions of aural and video energy probes which couple the aural and video energy from the circular wave guide to the helical antennas,

FIGURE 3 schematically illustrates how the aural energy probe is orientated within the circular wave guide,

FIGURE 4 schematically illustrates how the video energy probe is orientated Within the circular wave guide,

FIGURE 5 schematically illustrates the orientation of the aural energy and the video energy which is propagated in orthogonal modes within the circular wave guide by a transducer,

FIGURE 6 is a front elevational view of the transducer showing the aural energy input opening,

FIGURE 7 is a bottom view of the transducer showing the video energy input opening,

FIGURE 8 is a perspective view showing the detailed construction of the aural energy probe,

FIGURE 9 is a perspective view of a dual mode filter which is supported within the circular wave guide (as shown in dotted outline in FIGURE 2) and which functions to reflect video energy, and

FIGURE 10 is a sehmatic cross-sectional illustration of the choke short mounted at the top of the circular wave guide (as shown in dotted outline in FIGURE 2) which functions to reflect aural energy.

The orthogonal mode transfer system is described and claimed in the copending United States application of Paul M. Pan and Charles B. Mayer, Serial No. 646,769, filed March 18, 1957, and assigned to the same assignee.

FIGURES 11 to 14 illustrate different arrangements of the two helical antennas in accordance With other embodiments of the invention which employ side fire radiation and which are especially useful for multi-signal operation such as occurs in communications and television broadcasting. These embodiments may be used with the wave guide feeding system shown in FIGURES 1 to 10 or with coaxial line feeding systems;

FIGURE 11 shows part of a radiation system in which two helical antennas have the same diameter and pitch and are wound in opposite directions,

FIGURE 12 shows part of a radiation system in which two helical antennas are wound in opposite directions and have different diameters and pitches,

FIGURE 13 illustrates a portion of a radiation system with two parallel wound helical antennas having the same diameter and pitch, and

FIGURE 14 illustrates a portion of a radiating system in accordance with an embodiment of the invention which is particularly valuable for multi-channel television broadcasting and which employs two separate aural and video antenna systems having different diameters and pitches.

FIGURES l5 and 16 show end fire antenna systems in accordance with other embodiments of the invention which are particularly useful in communication and radar applications;

FIGURE 15 shows an antenna system especially valuable for diplexing and duplexing employing two parallel wound helical antennas of the same diameter and pitch,

FIGURE 16 illustrates an antenna system incorporating two cross-wound helices of the same diameter and pitch which may be used to radiate a signal with a preselected polarization or may be used to radiate two different signals simultaneously with cross polarization, and

FIGURE 17 shows a combined dual signal cross polarization system and a single signal selective polarization system for use with the antenna system shown in FIG- URE 16.

I. General description of helical antenna systems Helical antenna systems in accordance with the various embodiments of the invention may be grouped into two characteristic types, side fire and end fire.

In the side fire type, the helical antenna system is vertically orientated and the radiation pattern is generally horizontally polarized. More exactly, the volumetric radiation pattern of the side fire type is a surface of revolution about the antenna axis of a directive lobe normal to the axis. The radiation of an helical antenna system having an end fire characteristic is concentrated along the axis of the helical antennas and the radiation may be circularly or linearly polarized.

The side fire type is particularly useful in television broadcasting and in communication systems where receiving locations are in various directions. The end fire type is particularly useful for directed communications and in radar systems.

Both types may be arrayed; that is, a number of helical antennas may be supported end to end along a common axis. The side fire type when arrayed (stacked) produces a more concentrated radiation pattern in the direction normal to the helical antennas. The end fire type when arrayed has greater directivity and gain. The end fire type is directional but may be used with reflectors such as a parabolic dish if a super gain system is desired. In the end fire double helical cross-wound embodiment of the invention the type of polarization may be preselected by the station operator or two signals may be transmitted simultaneously with different polarization.

Each helical antenna comprises a series of single turns or helices. When the helix circumference is close to one wavelength and is driven between one end and a ground plane, the axial mode predominates; that is, the helical antenna is of the end fire type. If the circumference is approximately some integral multiple of a wavelength, for example, two or four wavelengths, and is driven between one end and a concentric conducting mast, the normal mode dominates; that is, the helical antenna is of the side fire type.

The single helical antenna is described and claimed in the copending United States application of Lloyd 0.

Krause and Howard G. Smith, Serial No. 271,374, filed February 13, 1952, now abandoned in favor of continuation application, Serial No. 732,482, filed May 2, 1958, now US Patent No. 2,985,878, issued May 23, 1961, which is assigned to the same assignee.

Each of the various embodiments of the invention has one major characteristic in common: each comprises at least two helical antennas which are wound around a common axis and which are fed separately. The two helices are preferably arranged to overlap in order to provide a compact arrangement.

Various embodiments of the invention may be used in television broadcasting to radiate the aural and video signals with little intercoupling. Various embodiments are especially useful for multi-signal operations such as occur in diplexing and duplexing applications in communication using the side fire or end fire modes. Various embodiments are useful for radar application, particularly where selection of the polarization is important such as in rainy weather.

A specific side fire embodiment of the invention designed for television broadcasting will first be described in detail by way of example. Thereafter, other side fire embodiments of the invention will be described which are especially useful for television broadcasting and communications. Then two end fire embodiments will be described in detail. These end fire embodiments are especially valuable in communication and radar applications. Finally, a dual signal cross polarization end fire system and a single signal selective polarization end fire system which may be used separately or together with the double helical crossavound embodiment of the invention will be described.

lI-A. General description of antenna system with wave guide feed A two-bay system for radiating video and aural energy in accordance with one embodiment of the invention in which two helical antennas are arranged with a common axis and are in partial overlap is shown in FIGURE 1.

The system generally comprises a circular wave guide 20, which also functions as a mast. The circular wave guide 20 is connected to the wave guide support 22 by means of the transducer 24 and the transformer 26 which are connected together. The wave guide support 22 in turn is mounted on support means such as the support mount 27 which may be a tower or the top of a high building.

A choke short 28 (FIG. 2) is connected at the top of the circular wave guide 20 and a dual mode filter 30 is supported within the circular wave guide 20.

Since the top and bottom bays of the two-bay system are similar, the top bay will be described first. An aural energy probe 32 (FIGS. 1, 2, 3 and 8) is mounted in an insulator 34 (FIG. 3), which is fixed Within the side of the circular wave guide 20, and projects toward the center of the circular wave guide 20. A video energy probe 36 is mounted in an insulator 38 (FIG. 4) and is positioned a distance below the aural energy probe 32 and ninety degrees around the circular wave guide 20 so that the video energy probe 36 projects towards the center of the circular wave guide 20 at a right angle to the aural energy probe 32.

The aural and video energy probes 32 and 36, the choke short 28, the dual mode filter 30 and the circular wave guide 29 can be considered as a coupling system for coupling energy propagated from the transducer 24 to the aural antenna 42 and video antenna 44 which comprise the antenna system,

Insulating means, such as the plurality of insulators 49 (FIGS. 1 and 2) or the equivalent, are supported around the circular wave guide 2% and support the aural antenna 42 which is connected to the aural energy probe 32 and the video antenna 44 which is connected to the video energy probe 36. The aural antenna 42 and the The flange 52 is connected to the 6 video antenna 44 are each of the helical type and in the illustrated embodiment are cross-wound around the circular wave guide 20 at their overlapping portion.

The bottom bay of the twobay system (FIG. 1) is similar to the top bay (except for the dual mode filter 3t and choke short 28) with corresponding parts indicated by the same reference character but with an a designation added.

Generally, the system operates in the following manner:

The aural energy is fed to the side of the transducer 24 (FIG. 1) and is propagated in the circular wave guide 20 in a given mode (FIG. 5). The video energy is fed via the wave guide support 22 and transformer 26 to the transducer 24 which propagates the video energy in a mode which is orthogonal to the mode of the aural energy. The aural energy probe 32 (FIG. 3) is orientated to be excited by the aural energy and not by the video energy, and the video energy probe 36 (FIG. 4) is orientated to be excited by the video energy and not by the aural energy. Therefore, there is practically no coupling between the video energy and aural energy within the circular wave guide 20. Further, since the aural antenna 42 and the video antenna 44 are separate from each other and are cross-wound, there is practically no coupling between the antennas. Thus, no substantial amount of energy is coupled from one transmitter to the other.

II-B. Transducer The transducer 24 (FIGS. 1, 6 and 7) functions to excite the video energy and aural energy in orthogonal modes with suificient bandwidth and isolationbetween the video energy input and the aural energy input.

The transducer 24 generally comprises the circular wave guide 46 having a rectangular aural energy opening 43 through its side for the aural energy input with a rectangular video energy opening 50 (FIG. 7) at its lower end for the video energy input.

A flange 52 (FIGS. 6 and 7) is coupled to a rectangular wave guide (not shown) which transfers the aural energy from the aural energy transmitter to the transducer 24. rectangular wave guide section 54- which is attached over the aural energy open.- ing 48 (FIG. 6). A resonant window 62 is provided for the aural energy opening 48 for matching purposes.

Video energy is transferred from the video energy transmitter via a rectangular wave guide (not shown) to the rectangular passage 5-5 (FIG. 7) in the transformer 26. The transformer 26 is connected at the top end to the flange 60 (FIG. 6) of the transducer 24. The bottom end of the transformer 26 is connected to the wave guide support 22 (FIG. 1) which is in the form of a wave guide extension of the wave guide (not shown) which feeds the video energy to the radiation system. The wave guide support 22 is connected by the insulating support connector 64 to the support mount 27.

In order to explain the operation of the transducer 24 and transformer 26, the wave guide terminology employed to describe various modes will be briefly explained.

A wave guide is a hollow pipe which is used for conducting electrical energy by reflecting waves back and forth along its length. Electrical energy is propagated within the wave guide in the form of waves. The waves can be defined in terms of wave length and mode of vibration. The wave length of a wave is a function of the period of time between corresponding parts in successive waves. The wave length is inversely proportional to frequency (i.e., the higher the frequency the shorter the wavelength) The mode of vibration relates to the three-dimensional field pattern of the waves. The mode of vibration of the electrical field in a rectangular wave guide is transverse, (i.e., from one side of the rectangular cross-section of the wave guide to the other). The modes are designated by the letters TE which stand for transverse electric. The

TE mode is further defined by one subscript which is the number of half-wave variations in field intensity to be found traveling one way across the rectangle and a second subscript which is the number traveling the other transverse dimension. Thus, the TE mode means the transverse electric mode having only one half-wave variation in field intensity across the long dimension of the rectangle and no variation across the short dimension of the rectangle. Thus, in the case of a rectangular wave guide, the TE mode is the only mode that will propagate if the narrow dimension of the rectangular wave guide is less than a quarter of a wavelength and therefore beyond cut-off. (The cut-oil frequency of a wave guide is the frequency at which the attenuation of the waves begins to rise rapidly because the rectangular dimension is not large enough to permit the waves to Vibrate back and forth along the side of the wave guide). Further, electrical energy in the T E mode can be fed from a rectangular wave guide to a circular wave guide having a circular cross-section sutficient in size to enclose a square having its side dimension substantially equal to the longer dimension of the rectangular cross-section of the rectangular Wave guide. This will permit the propagation of a TE mode in the circular wave guide and the TE mode is orientated in accordance with the orientation of the rectangular wave guide.

This principle makes possible the propagation of orthogonal modes within the circular wave guide 2% by the trans ducer 24 and the transformer 26.

The transformer 26 (FIG. 6) is a quarter-wave transformer section which matches the circular wave guide 46 to the rectangular wave guide support 22 (FIG. 1) which is of slightly different impedance. The transformer 26 which feeds the video energy to the circular wave guides 46 and 20 excites a TE mode from a TE mode in the wave guide support 22. The diameters of the circular wave guides 46 and 20 are the same and are chosen so that only the TE mode will propagate. Thus, video energy fed via the transformer 26 to the transducer 2 is propagated in the circular wave guide 20 in a specific mode (TE which is orientated in accordance with the orientation of the rectangular passage 56 in the transformer 25,

Aural energy in the TE mode is fed via the rectangular wave guide section 54 (FIG. 7) to the aural energy opening 48 (FIG. 6) and propagated in the circular wave guides 46 and 20 in the TE mode. Since the orientation of the aural energy opening 43 is perpendicular to the orientation of the rectangular passage 56 (FIG. 7) which forms the video energy opening 50, the aural energy is propagated in the circular wave guide 2t) in a mode at a right angle to the mode of the video energy. Further, since the aural energy mode is perpendicular to the orientation of the video energy opening 5%, the aural energy cannot propagate into the wave guide support 22 and be fed to the video transmitter. This is because the smaller perpendicular dimension of the video energy opening places it beyond cut-off; i.e., the perpendicular dimension of the video energy opening 50 is not large enough to permit the aural energy which is orientated at a right angle to it to pass through.

In addition, the aural energy opening 48 is arranged to be a quarter wavelength away from the effective position at which the short occurs. This prevents any video energy from being fed via the aural energy opening 48 to the aural energy transmitter because the aural energy opening 48 acts as a perfect short circuit for the video energy which propagates right through to the circular wave guide 20.

The resonant window 62 (FIG. 6) consists of the bars 68 and 70 positioned across the short sides of the rectangular aural energy opening 48 with the bar '72 positioned between the midpoints of the bars 68 and 79 across the aural energy opening 48. The resonant window 62 functions to prevent mismatch with respect to the video energy mode because the correct capacitance and react- 5 ance are chosen so that no resonant phenomenon will exist within the frequency band of operation.

The resonant window 62, due to its construction, also functions to increase the bandwidth of the system be cause the bars 63 and 7t) introduce inductive reactance and the bar 72 introduces capacitative reactance. This increases the bandwidth because it eliminates the mismatch of video energy as well as providing the correct reactauce to the aural energy. The resonant window 62 also eliminates the complicated method of matching by means of introducing either capacitance or reactance at different discontinuities to increase the bandwidth.

Thus, the transducer 24 functions to propagate the video energy and the aural energy in orthogonal modes in the circular wave guides 46 and 20 while preventing coupling between the aural and video energy openings 48 and 50 so that substantially all of the energy is transmitted to the circular wave guide 20 and substantially no energy is fed from one transmitter to the other.

It should be noted that other than orthogonal modes may be used, that the circular wave guide 20 may be replaced by a square wave guide, and that other than TE modes may be employed, but only at the expense of substantial complication with consequent reduction in efficiency and increase in cost.

II-C. Coupling system The aural and video energy in the circular wave guide 20 (FIG. 2) is coupled to the antenna system by means of a coupling system comprising the aural energy probe 32 and video energy probe 36 together with the choke short 28 and the dual mode filter 30. The dual mode filter 36 generally functions to pass the aural energy and reflect the video energy while the choke short 28 generally functions to reflect the aural energy.

Since the construction of the video energy probe 36 is the same as the construction of the aural energy probe 32, only the aural energy probe 32 will be described in detail. However, it should be noted that loops may be used inplace of the probes.

The aural energy probe 32 (FIG. 8) consists of the probe 80, the insulator 34 and the connector 82. The insulator 34 is preferably made of Teflon insulation and is threaded to mount in a threaded hole in the side of th circular wave guide 20. (FIG. 3). The insulator 34 is positioned so that the probe 80 is properly orientated with respect to the aural energy mode. The probe 80 is threaded so that the amount of projection of the probe 30 into the circular wave guide 20 is adjustable. The connector 32 (FIG. 8) is of trapezoidal shape with threaded holes such as hole 86 on each of the long sides to hold the ends of the helices.

If only one bay instead of the illustrated two-bay system is used, the aural energy probe 32 is designed to couple 100% of the aural energy to the aural energy antenna. If a two-bay system is used, then each aural energy probe 32 and 32a is adjusted to couple 50% of the aural energy to the associated aural antenna. The amount of coupling is a function of the amount of projection of the probe 80 into the circular wave guide 2% The video energy probe 36 is of the same construction as the aural energy probe 32. The video energy probe 36 is positioned ninety degrees around the circular wave guide 20 (FIGS. 2 and 4) and several half wavelengths away, for example, two and one-half wavelengths. The spacing of the aural energy and video energy probes 32 and 36 is mainly a function of the spacing of the associated antennas which is hereinafter described in detail.

The dual mode filter 3% (FIGS. 2 and 9) is positioned above the video energy probe 36 and functions to reflect the video energy while passing the aural energy. The dual mode filter 39 (FIG. 9) comprises the rectangular wave guide section 90 with the flanges 92 and 94 at its ends. Around the edges of each of the flanges 92 and 94 are the fingertip shorts 96 and 98 respectively which contact the inside of the circular wave guide 20 at periodic points. The plates of the flanges separate the video energy mode in one plane while transmitting the aural energy mode which is at right angles to the video energy mode.

The dual mode filter 30 is one-half wavelength in length and is mounted one or more quarter wavelengths above the video energy probe 36 (FIG. 2). The dual mode filter 30 provides a short to reflect the video energy to the video energy probe 36 and to transmit the aural energy with very little reflection. Thus, the dual mode filter 39 functions to decrease the coupling between the aural and video energy modes.

The choke short 28 at the top of the circular wave guide 20 (FIGS. 1 and 2) functions to insure 100% coupling of the aural energy to the aural antenna 22 by reflecting the aural energy back to the aural energy probe 32.

The choke short 28 (FIG. comprises the skirt 182 having the fingertip shorts 101 around its circumference. The fingertip shorts 101 contact the inside of the circular wave guide 26. The skirt 102, which is a quarter wavelength long, is connected to the cap 100 and is concentric to the circular wave guide 20. The diameter of the ca tee is less than the diameter of the circular wave guide 20 so that the skirt 102 is spaced from the circular wave guide 24 by an amount which produces the flange capacitance necessary for compensation; for example, .031 inch.

The effective position of the short provided by the choke short 28 is a number of quarter waves above the aural energy probe 32; for example, five quarter waves.

In summary, the aural and video energy propagated by the transducer 24 into the circular wave guide 26 is coupled to the antenna system while being isolated from each other.

II-D. Antenna system (FIGS. 1 and 2) A cross-wound helical antenna system in partial overlap in accordance with a specific embodiment of the invention is illustrated in FIGURES 1 and 2.

The aural antenna 42 and video antenna 44 each comprises a helical radiative conductor which extends in axially progressive turns about the circular wave guide 20, which functions as a conductive support structure. The aural antenna 42 and video antenna 44 in the top bay of the radiation system are each five wavelengths in length (aperture) having a diameter such that the circum-ference of each turn equals an integral number of wavelengths. The aural antenna 42, which is connected at its center to the aural energy probe 32, winds in one direction around the insulators 40 which encircle the circular Wave guide 2%). The video antenna 44, which is connected at its center to the video energy probe 36, winds in the same direction. The ends of each of the aural and video antennas 4 2 and 44 may be supported by beads.

Since the aural antenna 42 and video antenna 44 are displaced from each other by two and one-half wavelengths, the overlapping portions are cross-wound. The cross angle is preferably in the range of about twenty to about forty degrees. Grooves are cut at the crossover points to maintain the outside and inside circumference dimensions constant. Insulation sheets made from material sold under the trademark Teflon insulate the antennas from each other at the cross-over points.

The lower bay comprising the aural antenna 42a and the video antenna 44a are similar in construction and are connected to the aural antenna 42 and the video antenna 44 respectively.

The cross angle is a function of the spacing of the turns and may vary from about twenty degrees to about ninety degrees depending on the length (aperture) of the helices. Similarly, the necessary spacing of the aural energy probe 32 and video energy probe 36 (and therefore the associated antennas) has to be greater than one-sixteenth of a Wavelength. However, the greater the cross angle and the greater the probe spacing, the greater the longitudinal spacing of the aural antenna 42 and video antenna 44, and the greater the decoupling. It was found that a cross angle of about thirty degrees with probe spacing of two and one-half wavelengths provided a very good compromise between the lengths of each bay and the amount of decoupling.

It should be noted that any reasonable number of bays may be used, for example, ten bays can readily be stacked.

It should also be noted that other coupling means besides the probes may be used to couple the energy from the wave guide to the video and aural antennas; in particular, loops may be used which are suitably orientated to be separately excited by the aural energy and the video energy. In this sense, the loops are the exact equivalent of the probes.

The complete performance of an energy transfer system which includes a double helical antenna system in accordance with a specific embodiment of the invention illustrated in FIGURE 1 is given by way of example:

Greater than 23 db.

Greater than 40 db.

Greater than 23 db.

to each bay).

VSWR on aural input at :2%

bandwith less than 1.1. VSWR on video input at 1-3% bandwith Do.

Antenna Patterns:

Video energy pattern:

Horizontal-showed a 1.5 db cyclic efiect and the main null about 5 db Vertical-a half power beam width of 8 to 9 degrees Side lobe levels less than -14 db Aural energy pattern:

Substantially the same as the video energy pattern above.

III. Side fire antenna systems (FZGS. 1 and 11-14) In addition to the antenna system shown in FIGURE 1, other double helical antennas of the side tire type are shown in FIGURES 11 to 14. In the antenna system of FIGURE 1, the two helices are partially overlapped. In each of the antenna systems shown in FIGURES 11 to 14 the two helices are completely overlapped, that is, superimposed or mutually coextensive so that they occupy the same antenna aperture. Thus, a number of helical antennas can be arrayed to produce higher gain for the same length of antenna aperture since there is very little intercoupling.

Each of the illustrated side fire antenna systems may be used for diplexing or duplexing and therefore are particularly useful in both television broadcasting and communications. Further, each of the illustrated side fire antenna systems may be used with wave guide feeding systems of the type illustrated in the energy transfer system of FIGURE 1 or may be used with coaxial or other types of transmission line feeding systems in accordance with well known techniques.

The circumference length of each turn of the radiative conductor of each side fire helical antenna is usually an integral number of wavelengths, for example, 1, 2, 3 or 4. If circumferences of two or more wavelengths are used, which is preferred, then the currents at corresponding points on adjacent turns are in phase. The radiative conductor of each helical antenna extends in axially progressive turns about the mast (which functions as antenna support means) with a pitch which can vary from 0.5 to 0.6 wavelength. The pitch influences the phase velocity of the electromagnetic wave which in turn influences the antenna beam shaping.

In order to explain the theory of operation of the helical antenna systems, each helical antenna will be considered as an helical conductor and the mast will be considered as a cylindrical conductor.

The helical conductors and the cylindrical conductor together form sections of a radiating system. Electromagnetic energization applied between adjacent ends of the helical conductors and the cylindrical conductor cause electromagnetic waves to travel along the helical conductor away from the point of energization. As the electromagnetic waves travel along the helical conductor, they gradually decay in amplitude due to radiation of electromagnetic energy from the helical conductors. By making the helical conductors of sufficient length, reflections of electromagnetic waves from the remote ends of the helical conductors can be made substantially insignificant in effect.

A particular advantage of an antenna system of this character in which reflection elfects are minimized by making the helical conductors sufliciently long is that it presents a substantially constant impedance to the source of energization independent of frequency. The magnitude of this impedance is the characteristic impedance of the radiating system. Another advantage in making the helical conductors sulficiently long is that no problem arises in properly terminating the radiating system to minimize reflections.

The radial spacing of the helical conductors from the cylindrical conductor determines in large part the charac teristic impedance of the antenna system, that is, the greater the spacing the higher the characteristic impedance and vice versa.

The radial spacing of the helical conductors from the cylindrical conductor also determines in large part how long the helical conductors should be made in order to cause substantial radiation from the helical conductors with inappreciable reflection from the remote ends of these helical conductors.

In order to provide substantially uniform radiation in a plane transverse to the axis of the helical conductors, and

concentration of energy in the plane passing through the axis, it is essential that the conductor length of a single turn be substantially an integral number of wavelengths long, preferably two or greater. If a single turn is not equal to an integral number of wavelengths, a radiation pattern which is non-uniform in a plane transverse to the axis of the helical conductors results.

It should be noted that if a large number of turns are used in a helical section, the portions of the helical conductor in a particular transverse plane progressively farther from the end to which energization is applied are excited by currents of progressively different phase when the frequency of energization departs appreciably from a predetermined center frequency. Accordingly, in order to maintain the radiation characteristics of the antenna uniform for a broad band of frequencies, it is essential 'to keep the number of turns to a reasonable value.

In order further to confine the radiation in the axial planes, it has been found desirable to make the axial length of a single turn of the helical conductors equal to substantially one-half of the wavelength at the frequency of operation of the antenna system. With this arrangement the axial electric field components of the radiation from each helical conductor are small, and

the axial electrical field components from one helical conductor tend to cancel the axial electric field components of the other helical conductor. With this arrangement, the fraction of energy having axial electric field polarization, as distinguished from the desired transverse polarization, is reduced to a small value.

The spacing of the helical conductors with respect to the cylindrical conductor may be difierent for diiferent axial locations of the helical conductors. It may be desirable, for example, to change the current distribution along the helical conductors in order to produce a different radiation pattern transverse to the axis of the helices, or it may be desirable to change the impedance of the radiating helical conductor.

The pitch of the helical conductors also may be made different for different axial locations of the helical conductors to cause the formation of a difierent radiation pattern. For example, in order to cause a tilt of the axis of maximum transverse radiation, the length of the upper turns of the helix are made a fraction shorter than is required for all elements of the helix lying in a plane including the axis of the helix to be excited in the same phase, and the length of the lower turns of the helix are made a fraction longer than the above-described length.

The length of each of the helical conductors is determined principally by the radiation per unit length of the helical conductors which is, in turn, determined principally by the radial spacing of the helical conductors from the cylindrical conductor.

FIGURES 11 to 14 illustrate various embodiments of the end fire fully overlapped common axis double helical antenna system.

In FIGURE 11, a multi-bay antenna system is shown in accordance with another embodiment of the invention having one bay comprising the conductive mast which functions as support means for the helical antenna 122 and the helical antenna 124-. The helical antennas 122 and 124 are of the same diameter and pitch and are wound in opposite directions around the mast 120.

Each of the helical antennas 122 and 124 is supported by insulating means such as the insulators 126. Each of the helical antennas 122 and 124 comprises an axially progressive radiative conductor which extends about the conductive mast 120 from a two-terminalled feeding means such as the connector 130. The connector may be a coaxial connector if energy is fed to the antenna system via concentric transmission lines. If the connector 134 is in the form of a probe for use with a wave guide feeding system such as is shown in FIGURE 1, then the probe is one terminal and the mast is the other terminal. A support conductor 132 connects the helical antenna 122 to the connector 13%. The helical antenna 124 is fed by a similar system.

Additional antenna bays such as the antenna bay 138 may be arrayed or stacked along the conductive mast 124 In FIGURE 12, a multi-bay antenna system is shown in accordance with another embodiment of the invention having one bay comprising the conductive mast 140 which supports the helical antennas 142 and 144. In this antenna system the helical antennas 142 and 144 are cross-wound and have difierent diameters and pitches which increase the amount of decoupling. In particular, the helical antenna 142 has a larger diameter and pitch than the helical antenna 144.

Each of the helical antennas 142 and 144 may be supported by a plurality of insulators such as the insulators 126 (FIG. 11), or may be self supported by the conductive supports 146 and 148 as shown.

Other bays such as the bay 150 may be stacked along the same axis.

In FIGURE 13, a double helix antenna system is illustrated in accordance with another embodiment of the invention which comprises the helical antennas and 162 which may be supported about the conductive mast 13 164 and fed in the manner of the antenna system of FIGURE 11. The helical antennas 160 and 162 (FIG. 13) are parallel wound so that they are interlaced and have the same diameter and pitch.

In FIGURE 14, a double helix antenna system is illustrated in accordance with an embodiment of the invention which is particularly useful for multi-channel television broadcasting.

The antenna system comprises the conductive mast 170 which supports the helical antennas 172 and 174 by insulating means which may be similar to the insulating means of the antenna system of FIGURE 11. The helical antennas 172 and 174 are parallel wound but of different pitch and different diameter.

The helical antenna 172 may function as an aural antenna such as the aural antenna 42 (FIG. 2) for one television channel and the helical antenna 174 (FIG. 14) may function as an aural antenna for a second television channel. In this case other helices are supported in the manner shown in the antenna system of FIGURE 1 so that separate aural and video antennas are provided having one diameter and pitch for one television channel, and separate aural and video antennas are provided having a smaller diameter and pitch for the other channel. In this case, the circumferences of the antenna systems may be four wavelengths and two wavelengths, respectively.

The helical antenna system for one channel may be wave guide fed in the orthogonal-mode manner employed in the antenna system of FIGURE 1. In this case the conductive mast 170 would function as a wave guide. The helical antenna system for the second channel could also be wave guide fed, but with different type modes. Thus, orthogonal TE modes could be used for one channel and orthogonal TM, modes could be used for the other channel, and the respective probes which function as the feeding means for each helical antenna would be suitably orientated.

As an alternative, each helical antenna could be fed by a separate coaxial cable. Thus, there would be two coaxial cables to carry the video and aural energy for the one channel and two separate coaxial cables to carry the video and aural energy for the second channel.

It should be noted that an antenna system for more than two channels may be readily provided by arranging the helical antenna systems for each channel to be different in diameter and pitch. Thus, a four channel system could be used with helical antenna circumferences of two, three, four and five wavelengths respectively. Though each wavelength would be different, the spacing between the concentric helical antennas would still be more than ample.

1V. End fire antenna system (FIGS. 15 and 16) End fire antenna systems in accordance with other embodiments of the invention are shown, by way of example, in FIGURES 15 and 16.

A parallel wound double helical antenna sytem is shown in FIGURE 15 and a cross wound double helical antenna system is shown in FIGURE 16. In both antenna systems, the helical antennas are positioned along the same axis, are completely overlapped, and are separately fed by separate feeding means at their ends. In both antenna systems, the diameter of the helices are the same, although different diameters and pitches may be used in an antenna system. The diameter is chosen so that each turn or helix has a circumference in the range of about 0.25 wavelength to 1.3 wavelength and a pitch in the range of about 0.3 wavelength to 0.7 wavelength. A circumference of 0.65 wavelength with a pitch of .45 wavelength gives excellent results. However, the parallel wound embodiment radiates two circularly polarized waves which are polarized in the same direction. The cross wound embodiment can radiate a single signal with any polarization; that is, linear in both directions and circular in both directions, depending on the relative phase of the signals fed to the helical antennas. Both antenna systems may be fed with coaxial line or wave guide systems. Both antenna systems may be used for communications and radar applications.

In the embodiment of the invention shown in FIG- URE 15, two parallel wound interlaced helical antennas 18-0 and 182 of the same diameter and pitch are supported at one end by antenna support means such as the ground plane 184. The radiation is circularly polarized and is characterized as being left-hand polarized or right-hand polarized depending on the direction of turning of the helical antennas. This antenna system is particularly useful in communication either in duplexing or diplexing arrangements since there is little intercoupling and therefore no undue interference,

Each of the helical antennas 182 and 180 is wound around a support core 187 which is made of a dielectric material such as that sold under the trademark Poly- Form or any other low dielectric constant and low loss material. However, the helical antennas 182 and 184 could also be self-supporting.

The ground plane 184 functions to support the helical antennas and 182, to shape the beam pattern of the antenna system which is directional, and to complete the feeding system so that energy to be radiated is fed between each helical antenna and 182 and the ground plane 184.

Coaxial connectors 186 and 188, which function as two-terminalled feeding means, are mounted in spaced relation on the ground plane 184. The helical antennas 180 and 182 are mechanically and electrically connected to the center conductor of each of the connectors 186 and 188 which provide mechanical support. Energy from two transmitters may be fed to both helical antennas via coaxial cable (not shown) in order to radiate two separate signals (diplexing); or one helical antenna may be used for transmitting and the other for receiving at the same time (duplexing), since there is no substantial amount of coupling between the two helical antennas 180 and 182.

Circular polarization has been found to be particularly valuable in VHF PM communications systems. One reason is that a linear polarized wave when reflected changes polarization to some extent. Therefore, if mobile units such as cars are surrounded by higher objects, a wave initially transmitted with vertical polarization may be received by a vertically orientated antenna after reflection at a different polarization. When circularly polarized waves are reflected, there usually is a strong enough vertical component to insure adequate reception under most conditions.

Further, super gain can be achieved by using the antenna system shown in FIGURE 15 as a primary feed. It can be mounted in front of a parabolic dish (not shown) with the free ends of the helical antennas 180 and 182 near the focal point of the parabolic dish. Further, additional helical antennas may be arrayed to increase the gain and directivity of the antenna system. In addition, the ground plane 184 may be replaced by a 45 metallic cone if a more directive radiation pattern is desired.

The cross wound double helical antenna system 190 shown in FIGURE 16 comprises the helical antennas 192 and 194 which are supported by the coaxial con nectors 196 and 198, in turn, mounted on the ground plane 201). The helical antennas 192 and 194 may be airwound and self-supporting or wound on a suitable dielectric core. The helical antennas 192 and 194 are of the same diameter and length and are wound in opposite directions with insulation such as Teflon sheets separating the radiative conductors at the cross over points to prevent shorting.

The same signal may be fed to both of the helical antennas 192 and 194, or to either one separately, via

the coaxial cables 202 and 204 Which are connected to coaxial connectors 196 and 198 respectively.

As indicated above, a polarized wave can be specified as having right-handed or left-handed circularity. (More technically, this refers to the direction of rotation of the resultant E vector as it proceeds in the direction of propagation.) Therefore, the antenna system 19%) (FIG. 16) will radiate in one circular direction if the signal is fed to only one helical antenna. Similarly, the antenna system 190 will radiate in the opposite circular direction if the signal is fed only to the other helical antenna.

Non-circular polarization is obtained by feeding the same signal to both helical antennas but with a phase difference. For example, if the helical antenna 192 is fed a given signal and the helical antenna 194 is fed the same signal but 180 out-of-phase (push-pull), then the antenna system 190 will radiate signals of vertical polarization. This is because as a wave progresses down each helix in the same sense, one a positive wave, the other a negative wave, the currents in one are in timephase opposition to the other. This causes the horizontal components to cancel and the vertical components to add. The result is linear polarization in a particular vertical direction. If the coaxial feed lines are switched, vertical polarization in the opposite direction will result.

If both helical antennas 192 and 194 are fed the same signal in the same phase (push-push or parallel), the vertical component will cancel and the horizontal component will be added so that the antenna system 19% radiates a linearly polarized signal which is horizontal.

Other polarizations can be obtained by controlling the phase difference.

Polarization changing from linear to circular is used in many radar applications where the effects of rain are to be minimized. An antenna system which transmits a right-handed wave is relatively insensitive as a receiving device to a left-handed wave. It should be noted that a right-handed wave becomes a left-handed wave when reflected from a perfectly symmetrical surface. Since rain drops are roughly spherical in form, the reflections will approximate circularly polarized waves of opposite sense, while a non-symmetrical reflecting surface, such as an airplane, will reflect a signal of relatively poor circularity, or one possessing a large linear polarization component. Thus, when changing the polarization from linear to circular, there may be a target-to-precipitation ratio improvement of 8 to db.

Thus, the ability to use the antenna system of FIGURE 16 to determine the polarization of the radiated signals at will is also very useful in radar applications.

In communication it is very useful to be able to transmit two different signals from an antenna system. The embodiment of the invention shown in FIGURE 16 may also be used for this purpose, with the added ability to transmit the two signals with cross polarization. Thus, if a signal from one transmitter is fed to one of the helical antennas of the antenna system 190 and the same signal is fed to the other helical antenna with a 180 phase difference, the radiative signal will be vertically polarized.

If, simultaneously, a second signal from a second transrnitter is fed to one of the helical antennas in the same phase, with the first signal generated by the first transmitter, the signal will be radiated with horizontal polarization. Thus, one antenna system may be used to transmit two cross-polarized signals.

The frequencies of the two signals may be the same or different. Further, linear or circular polarization may also be selected by using the signal selective system 220.

A complete system for feeding the antenna system 199 is shown in block diagram form in FIGURE 17. The illustrated system comprises a single signal selective polarization system 220 combined with a dual signal crosspolarization system 230.

The single signal selective polarization system 229 comprises the transmitter 222, the hybrid junction 224 and 15 the feed line switch circuit 226 in series relation. The output of the feed line switch circuit 226 may be fed to the antenna system 1% via the antenna switch circuit 240.

The dual signal cross-polarization system 230 comprises the transmitters 232 and 222 and the hybrid junction 234 which also may feed the antenna system 190 via the antenna switch circuit 240.

The system select switch 250 together with the antenna switch circuit 240 functions to select which of the systems 220 and 230 feeds energy to the antenna system 190.

Each of the circuits, which are shown in block diagram form, is well known to those skilled in the art and therefore is not disclosed in detail.

When the system select switch 250 and the antenna switch circuit 241 are activated to select the single signal selective polarization system 220, the transmitter 222 is coupled to the hybrid junction 224 and the antenna system 196 is coupled to the feed line switch circuit 226.

The hybrid junction 224 functions, in response to a signal generated by the transmitter 222, to produce the generated signal and the same signal out-of-phase. The signals are fed to the selected helical antenna of the antenna system via the feed line switch circuit 226 and the feed lines 202 and 264 to produce vertical polarization in one direction as explained above. By effectively switching the feed lines 292 and 204 with the feed line switch circuit 226, the direction of polarization may be reversed.

When the system select switch 250 and antenna switch circuit 24% are activated to select the dual signal crosspolarization system, signals from each of the transmitters 222 and 232 are fed via the system select switch 250 to the hybrid junction 234 which functions to feed the two signals with the required phase difference via the antenna switch circuit 240 to the two helical antennas of the antenna system 190, which radiates the two signals in crosspolarization. The hybrid junction 234 isolates the transmitters 222 and 232 coupling.

from each other to prevent inter- Conclusion Therefore, in accordance with the invention, improved antenna systems have been provided which are particularly useful for multi-signal operation from the same location such as is required in television broadcasting, radar and communications, and which are relatively compact, simple to construct, easy to install, rugged, and effective in operation. In addition, antenna systems have been provided for radiating signals with preselected polarization or with cross-polarization. Further, the need for complicated and expensive filter equipment to prevent intercoupling of energy is lessened permitting high power and better quality transmission at a lower cost. Also, a number of bays may readily be arrayed axially to increase the gain of the antenna system.

While a number of specific embodiments of the invention have been described in detail, it should be apparent that many modifications and changes may readily be made without departing from the spirit and scope of the invention.

What is claimed is:

1. An antenna system comprising conductive means, a first radiative conductor disposed with respect to said conductive means, a second radiative conductor disposed with respect to said conductive means and having substantially the same axis as the axis of said first radiative conductor and overlapping said first radiative conductor, first feeding means coupled to said first radiative conductor and adapted to feed a first signal between said first radiative conductor and said conductive means, and second feeding means coupled to said second radiative conductor and adapted to feed a second signal between said second radiative conductor and said conductive means.

2. An antenna system comprising conductive antenna support means, a first radiative conductor supported by said conductive antenna support means, a second radiative conductor supported by said conductive antenna support means and having substantially the same axis as the axis of said first radiative conductor and substantially coextensive with said first radiative conductor, first feeding means coupled to said first radiative conductor and adapted to 'feed a first signal between said first radiative conductor and said conductive antenna support means, and second feeding means coupled to said second radiative conductor and adapted to feed a second signal between said second radiative conductor and said conductive antenna support means.

3. An antenna system comprising conductive antenna support means, a first helical radiative conductor supported by said conductive antenna support means, a second helical radiative conductor supported by said conductive antenna support means and the same axis as the axis of said first helical radiative conductor and occupying the same radiation aperture as said first helical radiative conductor, first feeding means coupled to said first helical radiative conductor and adapted to feed a first signal between said first helical radiative conductor and saidconductive antenna support means, and second feeding means separate from said first feeding means coupled to said second helical radiative conductor and adapted to feed a second signal between said second helical radiative conductor and said conductive antenna support means.

4. An antenna system comprising conductive means, a first helical radiative conductor disposed with respect to said conductive means, a second helical radiative conductor disposed with respect to said conductive means and having substantially the same axis as the axis of said first helical radiative conductor and overlapping and coextensive with a portion of said first helical radiative conductor, first feeding means coupled to said first helical radiative conductor and adapted to feed a first signal between said first helical radiative conductor and said conductive means, and second feeding means coupled to said second helical radiative conductor and adapted to feed a second signal between said second helical radiative conductor and said conductive means.

5. An antenna system comprising conductive antenna support means, a first helical radiative conductor supported by said conductive antenna support means, a second helical radiative conductor supportedby said conductive antenna support means along the same axis as the axis of said first helical radiative conductor and overlapping said first helical radi'ative conductor, turns of said first helical radiative conductor crossing turns of said second helical radiative conductor, first feeding means coupled to said first helical radiative conductor and said conductive antenna support means and adapted to feed a first signal between said first helical radiative conductor and said conductive antenna support means, and second feeding means coupled to said second helical radiative conductor and said conductive antenna support means and adapted to feed a second signal between said second helical radiative conductor and said conductive antenna support means.

6. An antenna system comprising conductive means, a first helical radiative conductor comprising a plurality of turns and disposed with respect-to said conductive means, a second helical radiative conductor comprising a plurality of turns and disposed with respect tosaid conductive means and having substantially the same axis as the axis of said first radiative conductor and overlapping said first radiative conductor, turns of said first and second helical radiative conductors being in substantially parallel relation, first feeding means coupled to said first helical radiative conductor and adapted to feed a first signal between said first helical radiative conductor and said conductive means, and second feeding means coupled to said second helical radiative conductor and adapted to feed a second signal between said having substantially- 18 second helical radiative conductor and said conductive means.

7. An antenna system comprising conductive antenna support means, a first helical radiative conductor supported by saidconductive antenna support means, a second helical radiative conductor supported by said conductive antenna support means along the same axis as the axis of said first radiative conductor and overlapping said. first radiative conductor, turns of said first helical radiative conductor crossing turns of said second helical conductor at an angle in the range of about 20 degrees to degrees, first feeding means coupled to said first helical radiative conductor and adapted to feed a first signal between said first helical radiative conductor and said conductive antenna support means, and second feeding means coupled to said second helical radiative conductor and adapted to. feed a second signal between said. second helical radiative conductor and said conducting antenna support means.

8. The antenna system of claim at an, angle. of 30 degrees.

9. An antenna system 7 wherein turns cross comprising conductive means, a first helicallradiative conductor comprising a plurality of turns and disposed with respect to said conductive means, a second helical radiative conductor comprising a plurality of turns and disposed with respect to said conductive means and having substantially the same axis as the axis of, said first radiative conductor and overlapping saidfirst radiative conductor, said first and second helical radiative conduct rs having different turns diameters, first feeding means coupled to said first helical radiative conductor .and adapted to feed a first signal between said first helical radiative conductor and said conductive means, and second feeding means coupled to said second helical radiative conductor and adapted to feed a second signal between said second helical radiative conductor and said conductive means.

10. An antenna system comprising conductive means, a first helical radiative conductor comprising a plurality of turns and disposed with respect to said conductive means, a second helical radiative conductor comprising a plurality of turns and disposed with respect to said conductive means and having substantially the same axis as the axis of said first radiative conductor and overlapping said first radiative conductor, turns of said first helical radiative conductor having a different pitch from that of the turns of said second helical radiative conductor, first feeding means coupled to said first helical radiativeconductor and adapted to feed a first signal between said first helical radiative conductor and said conductive means, and second feeding means coupled to said second helical radiative conductor and adapted to feed a second signal between said second helical radiative condu ctor and said conductive means.

11. An energy radiation system comprising a conductive support structure, first and second helical conductors supported by said conductive support structure along a common axis in overlapping relation, first and second feeding means for applying, energy between said conductive support structure and said first and second helical conductors respectively whereby electromagnetic energy to be radiated travels along the length of each of said first and second helical conductors, said first and second helical conductors havinga length so great relative to a wavelength of said energy that said energy is substantially radiated-before reaching the end of the associated helical conductor.

12. An energy radiation system comprising a conductive support structure, first and second helical conductors supported by said conductive support structure along a common axis in overlapping relation, first and second feeding means for applying energy between said conductive support structure and said first and second helical conductors respectivelywhereby, electromagnetic energy to beradiated travels along the length of each of said first and second helical conductors, said first and second helical conductors being arranged on said conductive support structure so that substantially little energy is coupled between said first and second helical conductors.

13. An energy radiation system comprising a conductive support structure, first and second helical conductors supported by said conductive support structure along a common axis in overlapping relation, first and second feeding means for applying energy between said conductive support structure and said first and second helical conductors respectively whereby electromagnetic energy to be radiated travels along the length of each of said first and second helical conductors, said first and second helical conductors having a length so great relative to a wavelength of said energy that said energy is substantially radiated before reaching the end of the associated helical conductor, said first and second helical conductors being arranged on said conductive support structure so that substantially little energy is coupled between said first and second helical conductors.

14. An energy radiation system comprising a conductive support structure, first and second helical conductors supported by said conductive support structure along a common axis in overlapping relation, the circumference of each of said first and second helical conductors being substantially an integral number of wavelengths, first and second feeding means for applying energy between said conductive support structure and said first and second helical conductors respectively whereby electromagnetic energy to be radiated travels along the length of each of said first and second helical conductors, said first and second helical conductors having a length so great relative to a wavelength of said energy that said energy is substantially radiated before reaching the end of the associated helical conductor, said first and second helical conductors being arranged on said conductive support structure so that substantially little energy is coupled between said first and second helical conductors.

15. An energy radiation system comprising a conductive support structure, first and second helical conductors supported by said conductive support structure along a common axis in overlapping relation, the circumference of each of said first and second helical conductors being in the range of about 1 to about 4 wavelengths, first and second feeding means for applying energy between said conductive support structure and said first and second helical conductors respectively whereby electromagnetic energy to be radiated travels along the length of each of said first and second helical conductors, said first and second helical conductors having a length so great relative to a wavelength of said energy that said energy is substantially radiated before reaching the end of the associated helical conductor, said first and second helical conductors being orientated on said conductive support structure so that substantially little energy is coupled between said first and second helical conductors.

16. An energy radiation system comprising a conductive support structure, first and second helical conductors supported by said conductive support structure along a common axis in overlapping relation, first and second feeding means for applying energy between said conductive support structure and said first and second helical conductors respectively whereby electromagnetic energy to be radiated travels along the length of each of said first and second helical conductors, said first and second helical conductors having a length so great relative to a wavelength of said energy that said energy is substantially radiated before reaching the end of the associated helical conductor, said first and second helical conductors being arranged on said conductive support structure so that turns of said first helical conductor cross turns of said second helical conductor.

17. The energy radiation system of claim 16 wherein turns of said first helical conductor wind in a direction 20 opposite to the direction of turns of said second helical conductor.

18. An antenna system comprising a conductive support structure, a first radiative conductor extending in axially progressive turns from said conductive support structure, a second radiative conductor extending in axially progressive from said conductive support structure having substantially the same axis and in overlapping relation with said first radiative conductor, a first two-terminalled feeding device, one terminal of said first feeding device being coupled to said first radiative conductor and the other terminal being coupled to said conductive support structure, and a second two-terminalled feeding device, one terminal of said second feeding device being coupled to said second radiative conductor and the other terminal being coupled to said conductive support structure.

19. The antenna system of claim 18 wherein said conductive support is a mast and said first and second radiative conductors encircle said mast.

20. The antenna system of claim 18 wherein said conductive support is a ground plane and said first and second radiative conductors extend from said ground plane.

21. An energy radiation system comprising a conductive support structure in the form of a ground plane, first and second helical radiative conductors supported by said support structure and wound about a common axis in overlapping relation, first and second feeding means for respectively applying energy between said first helical conductor and said conductive support structure and between said second helical conductor and said conductive support structure whereby electromagnetic energy to be radiated travels along the length of each of said first and second helical conductors, and means for coupling energy to said first and second feeding means in difierent phase relation.

22. The energy radiation system of claim 21 wherein all the turns of said first and second helical conductors have a circumference in the range of about 0.25 to about 1.3 wavelengths.

23. An energy radiation system comprising a conductive support structure in the form of a ground plane, first and second helical radiative conductors supported by said support structure and wound about a common axis in coextensive and overlapping relation, said first and second helical conductors having the same turns diameter, first and second feeding means for respectively applying energy between said first helical conductor and said support structure and between said second helical conductor and said support structure whereby electromagnetic energy to be radiated travels along the length of each of said first and second helical conductors, and means for controlling the phasing of said energy fed to said first and second feeding means in order to control the polarization of the energy radiated by said first and second helical conductors.

24. The energy radiation system of claim 23 wherein said first and second helical conductors are wound in opposite directions.

25. The energy radiation system of claim 23 wherein said first and second helical conductors are interlaced.

26. An energy radiation system comprising a conductive support structure in the form of a ground plane, first and second radiative helical conductors supported by said support structure and wound about a common axis in cross wound overlapping relation, first and second feeding means for respectively applying energy between said first helical conductor and said support structure and between said second helical conductor and said support structure whereby electromagnetic energy to be radiated travels along the length of each of said first and second helical conductors, first and second transmitters, and means for coupling energy generated by said first and second transmitters to said first and second feeding means respectively in different phase relation whereby said first and second helical conductors radiate energy from said first and second transmitters respectively in different polarization.

27. An energy radiation system comprising a conductive support structure in the form of a ground plane, first and second radiative helical conductors supported by said support structure and wound about a common axis in cross wound overlapping relation, first and second feeding means for respectively applying energy between said first helical conductor and said support structure and between said second helical conductor and said support structure whereby electromagnetic energy to be radiated travels along the length of each of said first and second helical conductors, first and second transmitters, and means for coupling energy generated by said first and second transmitters to said first and second feeding means respectively in dilferent phase relation whereby said first and second helical conductors radiate energy from said first and second transmitters respectively in cross polarization.

28. An energy radiation system comprising a conductive support structure in the form of a ground plane, first and second radiative helical conductors supported by said support structure and wound about a common axis in overlapping relation, first and second feeding means for respectively applying energy between said first helical conductor and said support structure and between said second helical conductor and said support structure whereby electromagnetic energy to be radiated travels along the length of each of said first and second helical conductors, a transmitter, switching means for coupling energy generated by said transmitter to said first and second feeding means and means for controlling the phasing of said energy fed to said first and second feeding means in order to control the polarization of the energy radiated by said first and second helical conductors.

29. Au energy radiation system comprising a conductive support structure in the form of a ground plane, first and second radiative helical conductors supported by said support structure and wound about a common axis in cross wound and overlapping relation, first and second feeding means for respectively applying energy between said first helical conductor and said support structure and between said second helical conductor and said support structure whereby electromagnetic energy to be radiated travels along the length of each of said first and second helical conductors, first and second transmitters, first phasing means for coupling energy generated by said first and second transmitters to said first and second feeding means respectively in different phase relation whereby said first and second helical conductors radiate energy from said first and second transmitters respectively in different polarization, second phasing means for controlling the phasing of energy fed from one of said transmitters to said first and second feeding means in order to control the polarization of the energy radiated by said first and second helical conductors, and switching means for switching said first and second feeding means to said first phasing means or said second phasing means.

30. The antenna system of claim 1 wherein said first and second signals convey different intelligence.

References Cited in the file of this patent UNITED STATES PATENTS 2,207,504 Bohm July 9, 1940 2,244,628 Kotowski June 3, 1941 2,351,055 Lakhovsky lune 13, 1944 2,403,500 Carlson July 9, 1946 2,471,515 Brown et a1. May 31, 1949 2,495,399 Wheeler Jan. 24, 1950 2,503,010 Tiley Apr. 4, 1950 2,511,611 Wheeler June 13, 1950 2,726,388 Kandoian et a1 Dec. 6, 1955 2,755,466 Klancnik July 17, 1956 2,800,656 Peterson July 23, 1957 2,835,893 Braund May 20, 1958 2,876,448 Guanella Mar. 3, 1959 WWW UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent N00 3 ,019 438 January 30, 1962 Paul M. Pan

that error appears in the above numbered pat- It is hereby certified ant requiring correction and that the said Letters Patent should read as corrected below.

Column 20 9 line, 7 before "from" insert, turns Signed and sealed this 19th day of June. 1962,

( SEAL) Attest:

DAVID L. LADD ERNEST W SWIDER Commissioner of Patents Attosting ()ffioer

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