US3761938A

US3761938A - Ferrite dipole antenna radiator

Info

Publication number: US3761938A
Application number: US00310735A
Authority: US
Inventors: F Reggia
Original assignee: US Department of Army
Current assignee: US Department of Army
Priority date: 1972-11-30
Filing date: 1972-11-30
Publication date: 1973-09-25
Anticipated expiration: 1990-09-25

Abstract

A ferrite rod is positioned between two parallel foil conductor strips. The strips terminate in perpendicular tabs which form a half-wavelength dipole antenna. Electromagnetic energy is coupled from free space to the ferrite rod by the dipole tabs. The energy propagates down the rod until reflected by a short circuit section connecting the ends of the conductor strips, opposite the tabs. After reflection, the energy propagates in a reverse direction. A coil carrying high frequency A.C. modulates the phase of the energy during propagation in both directions through the ferrite. When the energy is reflected back to the dispole tabs, the phase modulated energy is radiated to free space.

Description

[ Sept. 25, 1973 United States Patent [191 Reggia FERRITE DIPOLE ANTENNA RADIATOR Primary E.raminerEli Lieberman Inventor: Frank Reggia, Bethesda, Md. Atmmey Harry Saragovitz et [57] ABSTRACT A ferrite rod is positioned between two parallel foil 9 h St d a CV. em. mm Q mm m mmxm sd m mum t n m Uey 8mm h TrA e n .W 8 s A N 7 [22] Filed: 30, 1972 conductor strips. The strips terminate in perpendicular tabs which form a half-wavelength dipole antenna. Electromagnetic energy is coupled from free space to Appl. No.: 310,735

the ferrite rod by the dipole tabs. The energy propagates down the rod until reflected by a short circuit section connecting the ends ofthe conductor strips, opposite the tabs. After reflection, the energy propagates in 2 N 31 4 7 3 8 7 7 8H5 H 3 4 H3 3 4 m 5 8 H 7 u .u 3 n 4 u 3 nu mw .c Hr ..8 WW In .M I s sm UIF mum 555 a reverse direction. A coil carrying high frequency A.C. modulates the phase of the energy during propagation [56] References Cited in both directions through the ferrite. When the energy UNITED STATES PATENTS is reflected back to the dispole tabs, the phase modulated energy is radiated to free space 2,994,084 7/l96l Milleri..........

10 Claims, 3 Drawing Figures Patented Sept. 25, 1973 PARALILL PLANE RECIPROCAL PHASE SHIFTER (SINGLE PQRT) O Q o m w m w W seo soo-

4 l 80 I00 I O COIL CURRENT (m0) FERRITE DIPOLE ANTENNA RADIATOR RIGHTS OF THE GOVERNMENT The invention described herein may be manufactured, used and licensed by or for the United States Government for governmental purposes without the payment to us of any royalty thereon.

FIELD OF THE INVENTION The present invention is related to antenna radiators and more particularly to such a radiator that includes a ferrite-dipole radiator that modulates the phase of electromagnetic energy propagated through the radiator without the problems of amplitude modulation.

BRIEF DESCRIPTION OF THE PRIOR ART In the past, ferrite devices have been designed to cause phase modulation of microwaves passing through a waveguide. An example of this technology is disclosed in US. Pat. No. 3,274,516. This patent is directed to a waveguide of rectangular cross section having a ferrite rod disposed centrally therein. Along an intermediate length of the waveguide, opposite walls are cut out so that there only remains two parallel walls opposite each other. These walls set up a boundary for electromagnetic wave distribution, the propagation through this length of waveguide actually taking place in the ferrite rod, due to its high dielectric constant. As the energy propagates through the ferrite rod, a coil carrying high frequency A.C. generates an electromagnetic field that phase modulates the propagating energy.

Although the technique of phase modulation with a ferrite-coil combination has been successful in waveguides, there has been no recognition to date that this technique can be employed in a very small reflecting element which may be used as a microwave antenna radiator of an array that effects electronic scanning.

BRIEF DESCRIPTION OF THE PRESENT INVENTION The present invention is an improvement of the prior art. Specifically, structure is included which converts the waveguide of the prior art to a phase modulating antenna radiator. This is achieved by including a halfwavelength dipole structure that couples electromagnetic energy from space to the radiator. In addition, a short circuit section within the device allows the reflection of microwave energy that propagates along a ferrite rod after coupling from free space. After the en ergy is reflected, it reaches the dipole structure of the device, the phase modulated energy is radiated back into free space.

Thus, the present invention causes phase modulation of incoming microwaves. These microwaves are reflected back to radiating elements of the device without undesirable amplitude modulation.

The above-mentioned objects and advantages of the present invention will be more clearly understood when considered in conjunction with the accompanying drawings, in which:

BRIEF DESCRIPTION OF THE FIGURES FIG. 1 is a sectional mechanical representation of the present invention illustrating the principal components thereof.

FIG. 2 is a perspective view illustrating the exterior appearance of the present invention.

FIG. 3 is a plot of phase shift as a function of the modulating coil current, with microwave frequency as a parameter.

DETAILED DESCRIPTION OF THE INVENTION Reference numeral 10 generally denotes a mechanical sectional representation of the present ferrite dipole radiator. Reference numeral 12 generally indicates a pencil shaped ferrite rod that serves to concentrate microwave energy coupled from free space. The ferrite rod acts as a waveguide to allow the propagation of coupled electromagnetic energy along the length of the rod, from left to right in the diagram. These functions are preformed by the ferrite rod due to its high dielectric constant (e 13).

The ferrite rod includes a cylindrical portion 14 that terminates outwardly in a conical portion 16. The conical portion 16 extends outwardly into space as it does to achieve a proper impedance match with free space thereby achieving maximum energy transfer.

FIG. 1 illustrates a continuous thin copper foil strip generally indicated by reference numeral 18. This strip articulates into several different portions for distinct reasons.

Portions

20 and 22 are oppositely disposed parallel planes that serve as a boundary for electromagnetic energy distribution within the confines of the foil. Section 24 is an integral section of the foil strips that articulates from the right ends of the

portions

20 and 22. Portion 24 of the conductor strip serves as a microwave short circuit that causes reflection of impinging electromagnetic energy. At the opposite ends of the

sections

20 and 22 are perpendicularly articulating

tabs

26 and 28 that serve as half-wavelength dipole antenna elements for the remainder of the structure. The linear dimension between the axis of the ferrite rod and the outward edge of each dipole tab is one-quarter wavelength, as indicated.

In the basic operation of the radiator 10, the

dipole tabs

26 and 28 cooperate with the ferrite rod 12 to couple electromagnetic energy into the radiator from space. The rod serves as a waveguide and concentrates the coupled microwave energy for propagation down the length of the rod 12. The inclusion of the dipole tabs forms a larger and thus more efficient aperture for coupled energy. The radiator 10 is designed to effect the propagation of energy through the ferrite rod 12 in the dielectric mode HE This mode is a polarized or linear mode. The

parallel boundary conductors

20 and 22 insure that this mode is maintained. That is, the

foil boundary sections

20 and 22 suppress rotation of the electromagnetic field established in the HB mode. This rotation is known as Faraday rotation and is a well known phenomenon. By maintaining the dielectric mode, energy propagated through the ferrite rod 12 undergoes reciprocal phase modulation, as explained hereinafter, but amplitude modulation is suppressed. The short circuit section 24 reflects the energy back through the ferrite rod 12 in the same dielectric mode. When the reflected energy propagates to the conical portion 16 of the ferrite rod 12, the reflected energy, which is again phase modulated, is radiated back to free space by the combined structure of the ferrite rod 12 and the

dipole tabs

26 and 28. Since phase modulation obtained in the ferrite rod 12 is reciprocal, the total phase shift of the microwave energy in the above radiator is twice that which is obtained with microwave propagation in one direction through the ferrite rod.

As clearly shown in FIG. 2, an insulating body 30, preferably made from foam plastic; with a low dielectric constant, is positioned within the radiator device to surround the ferrite rod 12. The plastic is porous and serves to concentrate the coupled electromagnetic energy into the ferrite rod 12. It is not critical that the outward end of the insulating body 30 surround the conical portion 16 of the rod. However, it is not important that this material surround the entire length of the cylindrical portion 14 of the ferrite rod 12. The width of the plastic foam supporting the ferrite rod is the same as the width of the metal foil strip. This design allows for very high modulating frequencies.

A coil 32 surrounds the

parallel portions

20 and 22 of the strip conductor 18. The terminal leads 34 of the coil are connected to a source of high frequency AC. High frequency current in the coil allows rapid phase change in the ferrite rod and maximum efficiency occurs because no eddy current losses result during this condition due to the suppressing effect on eddy currents induced by the magnetic field generated by the coil. The fact that the foil strips terminate in an open circuit at both sides of the radiator insures the destruction of circumferential eddy current induced by the modulating coil.

A modification to the radiator structure can be achieved by using small permanent magnets in lieu of the coil 32. Thus, by positioning one or more magnets longitudinally with respect to the axis of the ferrite rod 12, the magnetic field generated by the magnets (36,38) casues a fixed phase shift of propagating energy. By pivotally mounting each magnet, such as with an adjustment screw 38, the magnets may be moved to achieve an adjustable fixed phase shift. This is particularly important if the present radiator is to be used in an application where energization of a coil is not practical or where fixed tuned phase shift is desirable without external control power. Although one magnet may be utilized, the figure illustrates the utilization of two oppositely disposed magnets which are more efficient than one magnet because it renders better magnetic field distribution through the device.

In operation of the present invention, each radiator can be employed to phase modulate electromagnetic energy coupled thereto. A number of these radiators can be positioned in an antenna array to achieve electronic scanning. It is important that the physical size of the individual radiating structures of an antenna array be very small so that their spacings can be kept less than one wavelength at the operating frequency. This is necessary for suppression of radiating sidelobes.

In terms of fabrication, the present invention is amenable to printed circuit fabrication techniques that can substantially reduce the cost of manufacture.

FIG. 3 illustrates a plot of phase shift as a function of coil current, with microwave frequency (9100 to 9600 MHz) being a parameter. These large magnitudes of phase shift were obtained with a very small radiating structure.

It should be understood that the invention is not limited to the exact details of construction shown and described herein for obvious modifications will occur to persons skilled in the art.

Wherefore, I claim the following:

1. A ferrite dipole antenna radiator comprising:

means having a high dielectric constant centrally positioned in the radiator for concentrating electromagnetic energy propagation therealong;

parallel boundary planes disposed in spaced parallel relationship from the high dielectric constant means; conductor means connecting the boundary planes for reflecting the energy impinging thereon after propagation along the high dielectric constant means;

and dipole means connected to the outward ends of the planes for radiating the reflected energy back into space.

2. The structure defined in claim 1 together with means having a low dielectric constant located between the high dielectric constant means and the planes for restricting energy propagation along the high dielectric constant means.

3. The subject matter defined in claim 2 wherein the high dielectric constant means comprises a ferrite rod.

4. The subject matter of claim 3 wherein the boundary planes are characterized by flat portions of conductor foil which articulate to the conductor means.

5. The subject matter of claim 4 wherein the dipole means are characterized by conductor tabs extending perpendicularly from the outward ends of the flat portions of the conductor foil.

6. The structure of claim 5 wherein the low dielectric constant means comprises an insulator body of foam plastic material.

7. The structure of claim 6 together with a coil transversely encircling the boundary planes and the ferrite rod, the coil carrying AC energization therein for creating a magnetic field that interacts with the propagating energy to cause phase modulation of the energy as radiated back out to free space.

8. The structure of claim 6 together with at least one permanent magnet mounted adjacent a boundary plane in a direction generally parallel with the rod for subjecting the propagated energy to a fixed magnetic field which causes a fixed phase shift of the propagated energy as radiated to free space.

9. The structure of claim 8 wherein the magnet is adjustably mounted with respect to the ferrite rod to effect an adjustable fixed phase shift.

10. The structure of claim 9 wherein a plurality of generally parallel magnets are adjustably mounted with respect to the ferrite rod for maximizing distribution of the fixed magnetic field around the rod.

Claims

1. A ferrite dipole antenna radiator comprising: means having a high dielectric constant centrally positioned in the radiator for concentrating electromagnetic energy propagation therealong; parallel boundary planes disposed in spaced parallel relationship from the high dielectric constant means; conductor means connecting the boundary planes for reflecting the energy impinging thereon after propagation along the high dielectric constant means; and dipole means connected to the outward ends of the planes for radiating the reflected energy back into space.