US3573833A

US3573833A - Broadband dielectric lens antenna fed by multiconductor quasi-tem lines

Info

Publication number: US3573833A
Application number: US843554A
Authority: US
Inventors: James S Ajioka; Raymond H Du Hamel
Original assignee: Hughes Aircraft Co
Current assignee: Raytheon Co
Priority date: 1969-07-22
Filing date: 1969-07-22
Publication date: 1971-04-06
Anticipated expiration: 1988-04-06

Abstract

The apparatus of the present invention provides a feed system utilizing a dielectric lens that is conical on one side and a truncated ellipsoid on the other, with the vertex of the cone coinciding with the focal point of the ellipsoid that is farthest from the convex side thereof. No less than two angular or conical conductors emanating from a multiple-port feed network are disposed longitudinally along the conical portion of the dielectric lens to the point of maximum lens diameter, whereat the conductors are connected together. To achieve monopulse capability and dual polarization, a multiconductor TEM line having no less than five conductors with the proper relative phasing therebetween is used to feed the lens. Proper relative phasing between lines is achieved with a broadband hybrid network.

Description

United States Patent [72] Inventors James S. Ajioka Fullerton; Raymond B. Du Hamel, Los Altos Hills, Calif. [21] Appl. No. 843,554 [22] Filed July 22, 1969 [45] Patented Apr. 6, 1971 [73] Assignee Hughes Aircraft Company Culver City, Calii.

[54] BROADBAND DIELECTRIC LENS ANTENNA FED BY MULTICONDUCTOR QUASl-TEM LINES 10 Claims, 2 Drawing Figs.

[52] US. Cl. 343/753, 343/783, 343/854, 343/911 [51] lntJl i ..H0lq 19/06 [50] FieldoiSarch 343/753, 754, 755, 783, 853, 911, 854

z-w'an A-Avflur;

[56] References Cited UNITED STATES PATENTS 3,389,394 6/1968 Lewis 343/753 3,321,763 5/ 1967 Ikrath et al. 343/754 Primary Examiner-Eli Lieberman Attorneys-James K. Haskell and Robert H. Himes ABSTRACT: The apparatus of the present invention provides a feed system utilizing a dielectric lens that is conical on one side and a truncated ellipsoid on the other, with the vertex of the cone coinciding with the focal point of the ellipsoid that is farthest from the convex side thereof. No less than two angular or conical conductors emanating from a multiple-port feed network are disposed longitudinally along the conical portion of the dielectric lens to the point of maximum lens diameter, whereat the conductors are connected together. To achieve monopulse capability and dual polarization, a multiconductor TEM line having no less than five conductors with the proper relative phasing therebetween is used to feed the lens. Proper relative phasing between lines is achieved with a broadband hybrid network.

Patented April 6, 1971 2 Sheets-Sheet 2 BROADBAND DIELECTRIC LENS ANTENNA FED BY MULTICONDUCTOR QUASl-TEM LINES The invention herein described was made in the course of or under a contract or subcontract thereunder with the Department of the Army.

BACKGROUND OF THE INVENTION Conventional feeds consist of a relatively small antenna such as, for example, a dipole, slot, log-spiral, or log-periodic antenna which illuminates a reflector or lens with a nonuniforrn spherical wave. The reflector converts the radiated spherical wave into a plane wave for maximum gain or possibly into a different spherical wave if a hyperboloidal reflector is used. in the case of antenna designed on the fourarm equiangular spiral concept, radiation is inherently circu larly polarized, which eliminates some of the components from the excitation and polarization assembly. However, to obtain both senses of circular polarization, feeding the spiral from the outer end as well as feeding from the center of the spiral has been tried, but with poor performance, because when fed from the outside, higher order radiating modes are encountered by the wave as it travels in toward the center before it reaches the active radius of the desired mode. Also, contrawound (clockwise and counterclockwise) spirals physically interfere with each other and cannot be used for dual polarization.

In another concept, a conical array of eight linearly polarized log-periodic elements provides sum and dilference patterns for both senses of circular polarization simultaneously. Because the relative phase between sum and difference beams is independent of frequency, tracking infonnation is easily obtained. It is difficult, however, to achieve satisfactory impedance or pattern characteristics of the log-periodic parasitic monopole elements. In addition, the phase center movement with frequency of even a successful log-periodic antenna used as a feed for a reflector or lens allows perfect focusing at only one frequency. The conical transmission line feed system of the present invention is simpler, less expensive, and has no phase center movement with frequency.

SUMMARY OF THE INVENTION The apparatus of the present invention provides an antenna system of more than a decade bandwidth with high directivity, monopulse capability and polarization agility. The system employs a conical or angular transmission line to guide a transverse electromagnetic (TEM) spherical wave through a dielectric lens which transforms the spherical wave into a wave with a planar phase front which radiates into space. Because a TEM wave has no cutoff frequency and the impedance, phase center location, and aperture field distribution are virtually frequency independent, the antenna system is frequency independent. The beamwidth, however, is limited by the aperture size of the lens in wavelengths. Monopulse operation with diverse circular polarization is achieved by using equally spaced multiconductor TEM lines with the proper interelement phase delays provided by a broadband hybrid feeding network. The monopulse sum mode utilizes the lowest even radiation pattern mode which requires the interelement phase between adjacent conical line elements to be 2-rr/n radians where n is the number of conical line elements and for the monopulse difference mode, the lowest odd radiation pattern mode is utilized in which the interelement phase is twice that of the sum mode. A two-conductor feed may be used to obtain a linearly polarized sum pattern. A three-conductor feed can provide two sum beams with opposite circular polarizations. A four-conductor feed can provide two circularly polarized sum beams and a degraded difference pattern. Five or more conductors are required for two circularly polarized sum and difference beams (four beams in all). In principle, for monopulse operation It must be at least three for single circular polarization and at least five for dual circular polarization. However, n is usually chosen for practical reasons convenient'for the particular broadband hybrid feed ing network used. Values of six and eight have been used successfully.

For highly directive constant beamwidth antennas, this lens is used as a feed for a reflector (or another lens). The reason for the constant beamwidth is due to the fact that the lens pattern beamwidth varies inversely with the frequency resulting in a reflector aperture illumination that is constant in terms of wavelengths, thereby insuring a constant beamwidth with frequency change.

In addition to monopulse sum and difference patterns, multiple overlapping beams (which can be used separately or as amplitude monopulse schemes) can be obtained by combining the sum and difference modes M1 M2 where M1 is mode 1 with phase progression Zrr/m a a.

BRIEF DESCRIPTlON OF THE DRAWINGS FIG. 1 illustrates a side view in perspective of the antenna system of the present invention with six angular conductors; and

FIG. 2 illustrates a block diagram of the sixport feed network of FIG. 1.

Referring now to H6. 1 to the drawings, there is shown a side view in perspective of the antenna system of the present invention. In particular, the antenna system includes a dielectric lens 10 constituting an ellipsoid that is truncated normal to the major axis thereof and a conical section 12 extending from the truncated surface to the left focal point 13 of the ellipsoid ll, as viewed in the drawing. The dielectric constant of the lens 10 is greater than unity.

In addition to the above, a circular conductor 15 is disposed about the truncated plane of ellipsoid 11. A conductive sheet 16 is connected to the conductor 15 and extends outwards therefrom normal to the major axis of the ellipsoid 11. A spacer disc 18 having an aperture in the center portion thereof and six uniformly spaced holes thereabout is placed over the vertex of the conical section 12 normal to the axis of rotation thereof. The aperture of the disc 18 is of the order of 1 inch in diameter to allow the vertex of conical section 12 to extend a comparable distance therethrough. Six flat conductors are disposed from the spaced holes in disc 18 to the circular conductor 15. The flat conductors 20-25 taper outwards to approximately midlength and then taper in for the remainder of the length. Optimum configuration of the flat conductors 20- --25 varies with the frequency. The six flat conductors 20- 25 about lens 10 are connected to a six-conductor TEM line 27 whereby the six conductors thereof constitute inputs to the antenna system and are designated T,T respectively. The terminals T,-T connect to a six-port feed network 28 which has 2 (summation) inputs 30, 31 and A (difference)

inputs

32, 33. The summation inputs 30, 31 feed the flat conductors 20- 25 about the lens 10 with progressively increasing or decreasing phase of 60 to produce single beams of right circular and left circular polarization. The

difference inputs

32, 33, on the other hand, feed the flat conductors 20-25 about the lens 10 with progressively increasing or decreasing phase of which accumulates to 720 in one revolution to generate dual beams of right circular and left circular polarization for tracking purposes. The right and left circular polarized beams may be operated simultaneously to generate a linear polarized beam that is poled in any desired direction.

Referring to H6. 2, there is shown a schematic block diagram of the six-port feed network 28 of FIG. 1. The six-port feed network 28 constitutes an emperical combination of quadrature hybrid and tapered-line magic-T networks. In FIG.

2 a convention is used in connection with the respective quadrature hybrids wherein the feed side comes out in phase quadrature with the nonfeed side and the label H refers to a 3 db. quadrature hybrid wherein the input power is divided equally between the two output terminals. ln addition, a convention is used in-connection with tapered line magic-T's wherein one side is defined as the 2" side. The label T refers to a 3 db. tapered-line magic-T for which the coupled outputs are split in power by the ratio lzl and the label T refers to a 4.8 db. tapered-line magic-T for which the coupled outputs are split in power by the ratio of 2:1 with the greater power output being on the 2 side. When feed is applied to the Z-side, the voltages appearing at the outputs are in phase and when the feed is applied to the non-2 side the voltages appearing at the outputs are l80 out of phase.

Referring now to FIG. 2, the six-port feed network 28 includes terminals 34-39 which connect, respectively, to terminals T,T and include 3 db. tapered-line magic-T's 40, 41, which have E-side outputs connected to terminals 35, 38 and the non-2 side outputs connected to terminals 36, 39, respectively. In addition, network 28 includes 4.8 db. tapered-line magic-T's 42, 43 which have i-side outputs connected to terminals 34, 37, respectively, non-2 side outputs connected to the Z-side inputs of tapered-line magic-

Ts

41, 40, respectively, and the E-side inputs terminated with

impedances

44, 45 respectively. An additional 3 db. quadrature hybrid 46 has an output 47 connected to the non-2 side input of 4.8 db. tapered-line tapered-line magic-T 41. Quadrature hybrid 46 has inputs 49, 50

opposite outputs

47, 48, respectively. Similarly, an additional 3 db. quadrature hybrid 51 has an output 52 connected to the non-2 side input of tapered-line magic-T 40 and an output 53 connected to the non-)1 side input of tapered-line magic-T 43. Quadrature hybrid 51 has inputs 54, 55 opposite the outputs 52, 53, respectively. Lastly, 3 db. tapered-line magic-Ts 60, 61 have E-side outputs connected to inputs 50, 55, and non-2 side outputs connected to

inputs

54, 49, respectively, of

quadrature hybrids

46 and 51. The E-side inputs of tapered-line magic-T's 60, 61 are connected to A-tenninals 32, 33, respectively, and the non-Eside inputs to Z-terrninals 31, 30, respectively.

In operation, a signal applied to E-tenninal 30 corresponds to a sum pattern excitation and produces progressive phases at the terminals T --T of 60. A signal applied to Z-tenninal 31, on the other hand, produces a sum pattern of the opposite circular polarization of phase progression of 60 at the terminals T -T Likewise, a signal applied to A-terminals 32 or 33 produces difference patterns with phase progressions of H20 or l20, respectively, at the terminals T,T The energy available at the terminals 34-39 progresses through the TEM line 27 to the flat conductors 20-25 which form a conical transmission line. The constant phase surfaces for the electric and magnetic fields are spheres centered at the focal point 13. Since the phase fronts for the transmission line wave are spherical, the lens will tend to transmit this wave as a plane wave. Sum patterns produce a single main beam and difference patterns produce two overlapping beams suitable for tracking purposes.

We claim:

1. A broadband antenna system comprising an ellipsoid of dielectric material of predetermined dielectric constant, truncated nonnal to the major axis thereof between one focal point and the extremity of said major axis farthest therefrom and a cone of dielectric material of said predetermined dielectric constant extending from the truncated surface of said el lipsoid to said one focal point, thereby to provide a dielectric lens;

a circular conductor disposed about the periphery of said truncated surface of said ellipsoid;

a plurality of no less than two equal length flat conductors disposed longitudinally along and at uniform intervals about said cone commencing from said circular conductor; and

a transmission line having a corresponding plurality of conductors connected to the respective extremities of said plurality of flat conductors farthest'from said circular conductor.

2. The broadband antenna system as defined in claim 1 wherein said predetermined dielectric constant is greater than unit 3 A broadband antenna system comprising an ellipsoid of dielectric material of predetermined dielectric constant truncated normal to the major axis thereof between one focal point and the extremity of said major axis farthest therefrom and a cone of said dielectric material extending from the truncated surface of said ellipsoid to said one focal point thereby to provide a dielectric lens;

a circular conductor disposed about the periphery of said truncated surface of said ellipsoid; and

means disposed on said cone of said dielectric lens for providing an n conductor conical transmission line from the vertex thereof to said circular conductor, n being an integer no less than two.

4. The broadband antenna system as defined in claim 3 wherein said n conductor conical transmission line includes n flat conductors having a taper from the center portion thereof.

5. The broadband antenna system as defined in claim 3 additionally including a conductive sheet extending outwards from said circular conductor.

6. A broadband antenna system comprising an ellipsoid of dielectric material of predetennined dielectric constant truncated normal to the major axis thereof between one focal point and the extremity of said major axis farthest therefrom and a cone of said dielectric material extending from the truncated surface of said ellipsoid to said one focal point thereby to provide a dielectriclens',

a circular conductor disposed about the periphery of said truncated surface of said ellipsoid; n equal length flat conductors disposed longitudinally along and at uniform intervals about said cone commencing from said circular conductor where n is an integer no less than two;

a TEM transmission line having n conductors connected to respective extremities of said n flat conductors farthest from said circular conductor; and

means connected to said TEM transmission line for feeding said n fiat conductors with signals having substantially equal phase differences from one conductor to the next adjacent conductor.

7. The broadband antenna system as defined in claim 6 wherein n is an integer no less than three and said substantially equal phase differences from one conductor to the next adjacent conductor constitutes a phase progression of 360/n.

8. The broadband antenna system as defined in claim 6 wherein n is an integer no less than three and said substantially equal phase differences from one conductor to the next adjacent conductor constitutes a phase delay of 360ln.

9. The broadband antenna system as defined in claim 6 wherein n is an integer no less than five and said substantially equal phase differences from one conductor to the next adjacent conductor constitutes a phase progression of 720n.

10. The broadband antenna system as defined in claim 6 wherein n is an integer no less than five and said substantially equal phase differences from one conductor to the next adjacent conductor constitutes a phase delay of 720/n.

Claims

1. A broadband antenna system comprising an ellipsoid of dielectric material of predetermined dielectric constant, truncated normal to the major axis thereof between one focal point and the extremity of said major axis farthest therefrom and a cone of dielectric material of said predetermined dielectric constant extending from the truncated surface of said ellipsoid to said one focal point, thereby to provide a dielectric lens; a circular conductor disposed about the periphery of said truncated surface of said ellipsoid; a plurality of no less than two equal length flat conductors disposed longitudinally along and at uniform intervals about said cone commencing from said circular conductor; and a transmission line having a corresponding plurality of conductors connected to the respective extremities of said plurality of flat conductors farthest from said circular conductor.

2. The broadband antenna system as defined in claim 1 wherein said predetermined dielectric constant is greater than unity.

3. A broadband antenna system comprising an ellipsoid of dielectric material of predetermined dielectric constant truncated normal to the major axis thereof between one focal point and the extremity of said major axis farthest therefrom and a cone of said dielectric material extending from the truncated surface of said ellipsoid to said one focal point thereby to provide a dielectric lens; a circular conductor disposed about the periphery of said truncated surface of said ellipsoid; and means disposed on said cone of said dielectric lens for providing an n conductor conical transmission line from the vertex thereof to said circular conductor, n being an integer no less than two.

6. A broadband antenna system comprising an ellipsoid of dielectric material of predetermined dielectric constant truncated normal to the major axis thereof between one focal point and the extremity of said major axis farthest therefrom and a cone of said dielectric material extending from the truncated surface of said ellipsoid to said one focal point thereby to provide a dielectric lens; a circular conductor disposed about the periphery of said truncated surface of said ellipsoid; n equal length flat conductors disposed longitudinally along and at uniform intervals about said cone commencing from said circular conductor where n is an integer no less than two; a TEM transmission line having n conductors connected to respective extremities of said n flat conductors farthest from said circular conductor; and means connected to said TEM transmission line for feeding said n flat conductors with signals having substantially equal phase differences from one conductor to the next adjacent conductor.

7. The broadband antenna system as defined in claim 6 wherein n is an integer no less than three and saId substantially equal phase differences from one conductor to the next adjacent conductor constitutes a phase progression of 360*/n.

8. The broadband antenna system as defined in claim 6 wherein n is an integer no less than three and said substantially equal phase differences from one conductor to the next adjacent conductor constitutes a phase delay of 360*/n.

9. The broadband antenna system as defined in claim 6 wherein n is an integer no less than five and said substantially equal phase differences from one conductor to the next adjacent conductor constitutes a phase progression of 720*n.

10. The broadband antenna system as defined in claim 6 wherein n is an integer no less than five and said substantially equal phase differences from one conductor to the next adjacent conductor constitutes a phase delay of 720*/n.