US3474453A - Whip antenna with adjustable tuning - Google Patents

Description

Oct. 21, 1969 F. E. IRELAND WHIP ANTENNA WITH ADJUSTABLE TUNING 2 Sheets-Sheet 1 Filed July 10, 1968 FIGZ INVENTOR FRANK IRELAN D FlG.l

ATTORNEY Oct. 21, 1969 F. E. IRELAND WHIP ANTENNA WITH ADJUSTABLE TUNING 2 Sheets-Sheet 2 Filed July 10. 1968 m M m I w 1 M F l 6 Ell v F 3 4 5 4 4 j T /III L '6 rr E F mvsmon FRANK IRELAND United States Patent Int. Cl. Hlllq 9/06 US. Cl. 343-745 16 Claims ABSTRACT OF THE DISCLOSURE This disclosure describes a high frequency antenna that includes a novel tuning means mounted in the antenna for tuning the antenna to a particular frequency band. The antenna includes at least one antenna element electrically connected to the tuning means. Electrically, the tuning means comprises a variable capacitor connected in parallel with an inductor. Mechanically, the tuning means comprises a tubular metallic shield mounted about an inductor coil. The shield is longitudinally movable, and, when moved, varies the capacitance between the shield and the coil and elements connected to the coil. Alternatively, a tuning slug is mounted in the coil and moves with respect to the coil so as to vary the inductance of the coil.

This application is a continuation-in-part of US. patent application Ser. No. 515,611, filed Dec. 22, 1965, now abandoned.

This invention relates to high frequency antennas and more particularly to a vertical mobile antenna havlng an improved radiating and/or receiving characteristic.

The prior art teaches that the well-known ground plane antenna composed of a vertical quarter-Wave radiating and/ or receiving element working against a quarter-wave characteristic horizontal ground plane has a high angle of radiation lobe pattern. It is also well known that a high angle of radiation is desirable for in flight communicauon with aircraft, but that there is a corresponding sacrifice in signal strength at ground level when such an antenna is used for ground level or mobile communications.

Even though vertical quarter-wave radiating element antennas have the foregoing ground level disadvantage, it is customary to mount such an antenna on a mobile vehicle for mobile communications. Such an antenna usually consists of a tubular electrically conducting structure which may rise to a height of 10 feet, for example. External means are usually provided for matching a load impedance to the antenna impedance for improving the radiating and/or receiving characteristic of the overall communications system at any one frequency.

It is also well known that it is often necessary to pro vide a single antenna of fixed length which is capable of satisfactory operation over a broad band of frequencies. To cover a desired band of frequencies, the usual practice is to provdie an external means for adjusting the impedance of a loading coil so that the antenna is nearly resonant at a particular frequency. It will be appreciated by those skilled in the art and others that this operation is not only time-consuming but also cumbersome since the radiating frequency may vary over a Wide band or even different bands. Because of this variation, frequent adjustments are necessary.

In addition to teaching that a quarter-wave antenna element Working against a horizontal ground plane having a quarter-wave characteristic radiates a vertical pattern, the prior art also teaches that a vertical antenna including a vertical half-wave element exhibits virtually right angle radiation provided that the base of the antenna is elevated above the reflective effect of the earth or other surice rounding objects. It is impossible, of course, to meet these height requirements in mobile communiaction antennas. Consequently, the best of the prior art antennas are greatly effected by the presence of earth or surrounding structures.

It Will also be appreciated that mobile antennas are subject to breakage and/or distortion as the result of striking the antenna against a foreign object. Hence, an electrically sectioned antenna composed of a plurality of parts is more economical and feasible than a solid antenna having the same radiating characteristics.

It is therefore an object of this invention to provide a vertical antenna having virtually right angle radiation or reception characteristics.

It is a further object of this invention to provide a vertical antenna having substantially right angle radiation or reception characteristics that is independent of earth ground when attached to a motor vehicle.

It is a still further object of this invention to provide a vertical antenna having substantially right angle radiation characteristics that is fed at one end to produce the highest maximum electro-magnetic field.

It is yet another object of this invention to provide a novel tuning device that cancels undesirable reactances.

It is yet another object of this invention to provide a tuning device suitable for use with an antenna that is mechanically rugged and electrically uncomplicated.

It is still another object of this invention to provide a tuning apparatus suitable for use with an antenna that is adapted to tune the antenna to radiate and/or receive signals in a predetermined frequency band.

In accordance with a principle of this invention, an antenna element is connected to a tunable means. The tunable means consists electrically of a capacitor connected in parallel with an inductor. The capacitor comprises a sleeve element mounted over an inductor coil. The sleeve element is axially movable so as to vary the area between the sleeve and the coil and elements connected to the coil. The variation in area creates a variable capacitance which varies the frequency of resonance of the parallel combination to thereby tune the antenna.

In accordance with another principle of this invention, the antenna element comprises a one-half wave length radiating element. The half-wave length element is separably attached to the tunable means at one end and the other end of the tunable means is connected to a suitable mounting means.

In accordance with a further principle of this invention, the antenna element consists of a pair of quarterwave length elements. One quarter-wave length element is separably attached to one end of the turnable means and the other quarter-wave length element is separably mounted between the tunable means and a mounting means.

In accordance with yet another principle of this invention, the tunable means includes a slug mounted inside of the coil. The slug is movable with respect to the coil so as to vary the inductance of the coil.

It will be appreciated from the foregoing description that the invetnion provides a rather uncomplicated means for tuning an antenna. The tunable means is mechanically strong and electrically uncomplicated, merely consisting of a fixed ferrule and a movable sleeve mounted over a coil. The sleeve provides mechanical strength, ease of adjustment and a shield for the coil. But, most important, the sleeve provides a means of adjusting capacity to a critical value to effect exact reactance cancellation. That is, tuning the antenna cancels undesirable reactances to prevent power loss caused by undesirable reactances. In addition, by providing a movable core inside of the coil, additional adjustment is provided. Further, by forming the invention of separable components, the antenna elements can be easily exchanged for longer or shorter elements as desired. In addition, if one of the elements is broken, it can be easily replaced.

It will also be appreciated that when the antenna is mounted on a motor vehicle body, the body does not form a part of the overall antenna radiation system as it does with prior art antenna systems. That is, most existing vehicle antennas, whether one-quarter wave, one-half wave or five-eights wave, are dependent on the vehicle body as part of the radiating system. This invention provides an easily tunable antenna system for cancelling reactance with little or no antenna loss that is independent of a vehicle body as part of the antenna radiating system.

The novel features of the invention, as well as the invention itself both as to its organization and method of operation, will be best understood from the following description when read in connection with the accompanying drawings wherein:

FIGURE 1 is an assembled antenna illustrating one embodiment of the invention;

FIGURE 2 is an exploded cross-sectional view of one embodiment of the tuning means of the invention;

FIGURE 3 is an electrical schematic representation of the embodiment of the invention illustrated in FIGURES l and 2;

FIGURE 4 is a schematic representation of the voltage distribution of an assembled antenna of the type illustrated in FIGURE 1 when tuned for a specific frequency;

FIGURE 5 is an assembled antenna illustrating an alternative embodiment of the invention;

FIGURE 6 is an exploded cross-section of an alternate embodiment of the tuning means of the invention;

FIGURE 7 is an electrical schematic of the embodiment of the invention illustrated in FIGURES 5 and 6; and

FIGURE 8 is a schematic representation of the voltage distribution of an assembled antenna of the type illustrated in FIGURE 5 when tuned for a specific frequency.

FIGURE 1 is a view of an assembled antenna wherein an upper quarter-wave antenna element 11 is coupled to a lower quarter-wave antenna element by a tuning element 25. The upper quarter-wave element 11 has a corona insulator 13 mounted on the upper end thereof. The lower quarter-wave element 15 is movably attached to a mounting plate 17 by a universal connector 19. Mounting plate 17 is shown as attached to a vehicle side 21. A coaxial cable 23 connects the lower end of the element 15 with a transmitter/receiver (not shown).

One embodiment of the tunable portion 25 of the antenna is shown in detail in FIGURE 2. An insulated copper were 27 is wound to form a coil about a fiberglass insulating core 29. A brass sleeve 31, having external threads 33, a counter bore 35, and an internal tap 37, is attached to the core 29 by a pin 30, for example.

Electrical contact 39 is made between the coil 27 and the sleeve 31 by any of the well known methods such as brazing, spot welding, or silver soldering, for example.

A second tapped brass sleeve 41 having internal threads 43 and a counter bore 45 is attached to core 29 by a second pin 44. Electrical contact 44 is made between the sleeve 41 and the coil 27 by any of the well known methods hereinabove set forth.

The internal threads 43 of the lower sleeve 41 are adapted to accept the threaded portion of the lower antenna element 15. Likewise, the counter-bore portion 35 of the upper sleeve 31 is designed to accept a shoulder portion 51 of the upper antenna element 11. A lower tapped portion of the upper element 11 is threaded into the tapped area 37 of the upper sleeve 31.

An adjustable conductive sleeve 53 having internal threads 55 is cooperatively mounted on the outer threaded portion of the upper brass sleeve 31. A locking nut 57 is also threaded on the upper brass sleeve 31 and cooperates to maintain the adjustable sleeve 53 in a desired position.

An O-ring element 56 is mounted between the lower portion of the adjustable conductive sleeve 53 and the outer periphery of the lower brass sleeve 41. This O-ring maintains a capacitive separation between the adjustable conductive sleeve 53 and the lower brass sleeve 41. In addition, the O-ring adds to the lateral strength of the overall structure. The O-ring may be held in the adjustable conductive sleeve 53 by an internal peripheral slot, for example.

The adjustable sleeve 53 in combination with the brass sleeve 41 and the coil 27 forms an adjustable capacitor which is electrically connected in parallel with the coil 27. This parallel circuit will resonate at a frequency determined by the adjustment of the sleeve. The electrical circuit which is representative of the foregoing mechanical interconnection is illustrated in FIGURE 3. That is, FIGURE 3 illustrates a variable capacitor connected in parallel with a fixed coil.

FIGURE 4 is a schematic representation of the instantaneous vector voltage of the antenna when tuned for maximum efficiency. More specifically, in order to achieve high radiating and/ or receiving characteristics for the antenna, it is necessary that the antenna be tuned to cancel the reactance between points 59 and 61 shown in FIGURES 3 and 4. This cancellation is performed by adjusting the tuning element to a resonant or near resonant state for the frequency of operation. In addition to compensating for the reactancc that occurs in an ideal situation, it will be obvious to one skilled in the art that slight deviations in reactance caused by incorrect antenna length is also compensated for by resonating the tuned circuit.

It will be appreciated by those skilled in the art and others that the primary purpose of the tuned element is to perform the function of a quarter-wave shorted stub line wherein a 180 phase displacement exists across the points of connection so that there is a non-radiating quarterwave coupling between the two quarter-wave radiating elements. This results in a narrow radiation pattern that, as best understood, is caused by the distorted top and bottom lobes which combine to form in effect a vertical beam antenna. That is, the instant antenna is designed to lower the angle of radiation by separating the upper approximate quarter-wave radiating antenna element from the lower approximate quarter-wave radiating with a fixed coil and a variable air condenser which are mounted so as to form a parallel resonant circuit very close to the operating frequency. This resonant circuit (or closely resonant circuit) forms a tuned stub allowing maximum voltage to appear at the center of the coil with voltages of opposite instantaneous polarity appearing at both ends of the coil (or stub). This action separates the upper half of the antenna from the lower half of the antenna so two waves are radiated forming a single complex wave front having a flattened lobe and therefore greater effective voltage gain in the desired direction.

It will be appreciated that if either of the antenna elements 11 or 15 are damaged, they may be easily replaced with similar elements because of the separable nature of the mechanical construction of the invention.

It will also be appreciated that once the tuned circuit is tuned using the variable capacitance, the locking nut is tightened to prevent any change in tuning due to vibration and the like.

FIGURES 5-8 illustrate an alternative embodiment of the invention wherein the lower quarter-wave antenna element is eliminated and the upper quarter-Wave antenna element is replaced by a one-half Wave length element. In addition, the core is eliminate from the coil and a tuning slug 73 is inserted in a hollow space inside of the coil 27 and the core 29. The tuning slug 73 is attached to a shaft 75 that is threaded in the upper sleeve 53. By rotating the shaft 75 the slug 73 is vertically moved inside of the coil 27. Movement of the slug 73 varies the inductive effect of the coil 27 in a manner well known in the art. If desired, a lock nut can be included for locking the setting of the slug in place. FIGURE 7 illustrates, electrically, the parallel arrangement of the variable capacltor sleeve arrangement heretofore discussed with respect to FIGURE 2 and the coil of variable inductance 27. By providing an adjustable inductance in parallel with an adjustable capacitance, the range of the overall tuned circuit is increased. That is, the tuning element illustrated in FIGURES 5 and 7 can be tuned to frequencies over a greater range than the tuning element illustrated in FIGURES 1-3.

While the frequency range of the embodiment of the invention illustrated in FIGURES 5-8 is increased, the operation of the invention remains identical to the embodiment of the invention illustrated in FIGURES l-4 hereinabove discussed. That is, the tuned circuit is adapted to tune the antenna so that undesirable reactance is cancelled. The one-half wave length element forms a pattern that has a flattened lobe and therefore greater voltage gain in the desired direction-The tuning element operates as a stub. And, the adjustable sleeve 53 provides a shield so that the radiation of the tuning element has no etfect on the overall operation of the antenna.

It will be appreciated by those skilled in the art and others that applicant has provided a relatively uncomplicated and inexpensive tunable mobile antenna. Although specific structure has been described, it will be appreciated that the scope of this invention includes various changes and modifications not specifically discussed. For example, the tunable element illustrated in FIGURE 6 can be used with the embodiment of the antenna illustrated in FIGURE 1, i.e., an embodiment including two quarter-wave length elements. Alternatively, the embodiment of the tuning element illustrated in FIG- URE 2 can be utilized with the embodiment of the antenna illustrated in FIGURE 5. Moreover, other tuning elements can be used. In addition, it will be appreciated that more than one tuned circuit can be utilized in the invention. That is, by properly stacking a plurality of tuned elements increased gain is provided. Further, wide variations in the size and shape of the inductive and capacitive elements fall within the scope of the invention. Moreover, bank winding, powdered iron cores and multiplate condensers can be used in the invention when low frequency ranges are to be covered by a transmitter and/or receiver connected to the antenna. Hence, the invention can be practiced otherwise than as specifically described herein.

It will also be appreciated that the invention provides a convenient and easy method of tuning an antenna through resonance. The critical point may be approached from either side with ease and the tuning sleeve may be locked in a selected position.

In addition to its use as an antenna tuning element, the tuning element herein disclosed is useful in other environments. For example, it can be used as a filter to reject spurious signals. Alternatively, it can be attached to a tower, building, tank or other conducting structure and tuned to cancel unwanted reactance. And, it will serve as a tuning element in a gamma match stub.

What is claimed is:

1. An antenna tuning device comprising:

a longitudinal insulating core having a longitudinal axis;

a coil wound around the longitudinal axis of said core;

a first electrical conducting sleeve element mounted over one end of said core so that it is in electrical contact with one end of said coil; second electrical conducting sleeve element mounted over the end of said core so that it is in electrical contact with the other end of said coil; and movable sleeve element mounted for longitudinal movement along the outer periphery of said first electrical conducting sleeve, said movable sleeve element extending over said core and coil to said second electrical conducting sleeve.

2. An antenna tuning device as claimed in claim 1 wherein the outer periphery of said first electrical conducting sleeve is threaded and the inner periphery of said movable sleeve element is tapped.

3. An antenna tuning device as claimed in claim 2 including a lock nut coacting with said first electrically conductive sleeve element and said movable sleeve element to lock said movable sleeve element in predetermined positions.

4. An antenna tuning device comprising:

a coil having a longitudinal axis;

a slug movably mounted along said longitudinal axis of said coil;

a first electrical conducting sleeve element mounted so that it is in electrical contact with one end of said coil;

a second electrical conducting sleeve element mounted so that it is in electrical contact with the other end of said coil; and movable sleeve element mounted for longitudinal movement along the outer periphery of said first electrical conducting sleeve, said movable sleeve element extending over said coil to said second electrical conducting sleeve.

5. An antenna tuning device as claimed in claim 4 wherein the outer periphery of said first electrical conducting sleeve is threaded and the inner periphery of said movable sleeve element is tapped.

6. An antenna tuning device as claimed in claim 5 including a lock nut coacting with said first electrically conductive sleeve element and said movable sleeve element to lock said movable sleeve element in predetermined positions.

7. An antenna comprising:

a longitudinal insulating core having a longitudinal axis;

a coil Wound around the longitudinal axis of said core;

a first electrical conducting sleeve element mounted over one end of said core so that it is in electrical contact with one end of said coil;

a second electrical conducting sleeve element mounted over the other end of said core so that it is in electrical contact with the other end of said coil; movable sleeve element mounted for longitudinal movement along the outer periphery of said first electrical conducting sleeve, said movable sleeve element extending over said core and coil to said second electrical conducting sleeve; and

an antenna element electrically connected to said first electrical conducting sleeve element.

8. An antenna as claimed in claim 7 wherein the outer periphery of said first electrical conducting sleeve is threaded and the inner periphery of said movable sleeve element is tapped.

9. An antenna as claimed in claim 8 including a lock nut coacting with said first electrically conductive sleeve element and said movable sleeve element to lock said movable sleeve element in predetermined positions.

10. An antenna as claimed in claim 9 wherein said antenna element is formed of two quarter-wave length elements, one quarter-wave length element electrically connected to said first electrical conducting sleeve element and the other quarter-wave element electrically connected to said second electrically conducting sleeve element.

11. An antenna as claimed in claim 9 wherein said antenna element is a one-half wave length element.

12. An antenna comprising:

a coil having a longitudinal axis;

a slug movably mounted along said longitudinal axis of said core;

a first electrical conducting sleeve element mounted so that it is in electrical contact with one end of said coil;

a second electrical conducting sleeve element mounted so that it is in electrical contact with the other end of said coil;

a movable sleeve element mounted for longitudinal movement along the outer periphery of said first electrical conducting sleeve, said movable sleeve element extending over said coil to said second electrical conducting sleeve; and

an antenna element electrically connected to said first electrically conducting sleeve element.

13. An antenna as claimed in claim 12 wherein the outer periphery of said first electrical conducting sleeve is threaded and the inner periphery of said movable sleeve element is tapped.

14. An antenna as claimed in claim 13 including a lock nut coacting with said first electrically conductive sleeve element and said movable sleeve element to lock said movable sleeve element in predetermined positions.

15. An antenna as claimed in claim 14 wherein said antenna element is formed of two quarter-Wave length elements, one quarter-wave length element electrically connected to said first electrical conducting sleeve ele- References Cited UNITED STATES PATENTS 2,941,204 6/1960 Bailey 343-745 2,059,186 10/1936 Brown 343-752 3,064,257 11/1962 Guest 343--747 3,226,725 12/1965 Ritchie et al. 343--750 3,264,647 8/1966 Nuttle 343750 ELI LIEBERMAN, Primary Examiner US. Cl. X.R.

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