US3560984A

US3560984A - Broadband circularly polarized antenna having a continuous rectangular aperture

Info

Publication number: US3560984A
Application number: US783047A
Authority: US
Inventors: Tsze K Lee; Arthur Winkler; Wai Wong
Original assignee: Loral Corp
Current assignee: Lockheed Martin Tactical Systems Inc
Priority date: 1968-12-11
Filing date: 1968-12-11
Publication date: 1971-02-02
Anticipated expiration: 1988-02-02

Abstract

A BROADBAND CIRCULARLY POLARIZED ANTENNA HAVING A CONTINUOUS RECTANGULAR APERTURE TO OBTAIN CIRCULAR POLARIZATION, HAVING UNIFORM PHASE AND TAPERED AMPLITUDE ILLUMINATION OVER THE BROAD DIMENSION OF THE APERTURE. THE DEVICE FEATURES A LARGER EFFECTIVE RADIATING OR RECEIVING APERTURE THAN COMPARABLE RECTANGULAR ARRAY OF CIRCULARLY POLARIZED SPIRALS DUR TO THE USE OF VIRTUALLY LOSSLESS RADIATING

ELEMENTS TO PROVIDE HIGHER GAIN. LINEARLY POLARIZED RADIATING ELEMENTS ARE UTILIZED TO FEED AN APERTURE WITH LINEARLY POLARIZED ENERGY WHICH IS THEN TRANSFORMED INTO CIRCULARLY POLARIZED ENERGY BY MEANS OF A POLARIZER GRID.

Description

United States Patent O 3,560,984 BROADBAND CIRCULARLY POLARIZED ANTENNA HAVING A CONTINUOUS RECTANGULAR APERTURE Tsze K. Lee, New Rochelle, Arthur Winkler, Bronx, and

Wai Wong, Plainview, N.Y., assignors to Loral Corporation, Scarsdale, N.Y., a corporation of New York Filed Dec. 11, 1968, Ser. No. 783,047 Int. Cl. H01g 15/24, 21/08, 13/02 U.S. Cl. 343-756 3 Claims ABSTRACT OF THE DISCLOSURE This invention relates generally to the field of circularly polarized transmitting antenna particularly suited for broadband communication or reception for ECM and other similar applications.

It is among the principal objects of the present invention to provide an improved antenna construction in which azimuth and elevation beamwidths may be simply controlled by aperture size, using a single monopole array.

Another object of the invention lies in the provision of an improved antenna construction in which greater gain is available as compared with comparable rectangular array spiral constructions known in the art.

A further object of the invention lies in the provision of improved antenna construction offering shorter depth and superior aperture illumination control, as compared with conventional sectoral horn and polarizer constructions.

Still another object of the invention lies in the provision of improved antenna construction in which superior reproducibility and ease of fabrication are realized as cornpared with rectangular array of spiral constructions.

A feature of the disclosed embodiment lies in the fact that multiple arrays may be vertically stacked to obtain a two dimensional array, where required.

These objects and features, as well as other incidental ends and advantages, will more fully appear in the progress of the following disclosure, and be pointed out in the appended claims.

In the drawing, to which reference will be made in the specification, FIG. l is a front elevational view of an embodiment of the invention.

FIG. 2 is a transverse sectional view thereof as seen from the plane 2-2 in FIG. 1.

FIG. 3 is a bottom plan as seen from the plane 3 3 in FIG. l.

In accordance with the invention, the device, generally indicated by reference character 10, comprises broadly: a rectangular channel cavity element 11, a polarizer grid element 12, and a plurality of monopole elements 13.

The rectangular channel cavity element 11 may be of conventional sheet metal construction, including a rear wall 15, an upper wall 16, and a lower wall 17 defining a cavity area 18. Flared

portions

19 and 20 communicate 3,560,984 Patented Feb. 2, 1971 lCe with

flange portions

21 and 22, and support a strip of re` sistive card 23 through a foam material support 24.

The polarizer grid element 12 includes first, second and third photo-etched

gratings

30, 31 and 32, respectively, maintained in space parallel relation by a pair of

dielectric spacers

33 and 34 and two edge retaining rims 35.

The monopole elements 13 are similar, and are mounted by connector members 39 in front of the rear wall 15, as best seen in FIGS, 2 and 3 in the drawing.

In a preferred embodiment, the channel cavity element is nine inches long, 0.5 inch high and one inch deep. The monopoles are spaced 0.75 inch on centers. The depth of the channel is extended in the forward direction by aring to a desired vertical aperture of 1.53 inches. The polarizer grid is nine inches long by 2.25 inches high by 0.5 inch thick, and serves to convert linear polarization to circular polarization. The resistive card is placed parallel to the axis of wave propagation, and serves to suppress unwanted orthogonal linear polarization. The antenna pattern is nominally circularly polarized with a narrow azimuth beamwidth and a broad elevation beamwidth.

Excitation of the monopole elements is obtained through a printed circuit feed network (not shown) of conventional type which provides symmetrically tapered amplitude illumination and uniform phase across the monopole array. A hybrid input (not shown) to the feed network provides sum and difference radiation patterns.

A device constructed in accordance with the above description was measured over a bandwidth of 1.4721 in X- band, the results being summarized as follows.

Gain measurements were taken at the output of the sum channel of the hybrid. The gain of the maximum polarization response at the peak of the beam varies from 11.5 to 12 db over the band with an average value of 13.5 db. Gain is referred to a linear isotrope.

The side lobe level is a function of the illumination. For the chosen illumination, the largest side lobe is 16.5 db down from the peak of the sum beam for horizontal polarization. Elsewhere over the band, the side lobe level is generally at least 20` db down over most of the band for both orthogonal linear polarizations.

The voltage standing wave ratio at the input to the hybrid sum channel shows a maximum ratio of 4.0:1 at one frequency near the low end of the frequency band. Over the greater portion of the band the ratio is under 2.0:1.

The axial ratio measured at the peak of the sum beam is less than 2.0 db over most of the band except at the low end where a maximum of 3.1 db is obtained.

We wish it to be understood that we do not consider the invention limited to the precise details of structure shown and set forth in this specification, for obvious modications will occur to those skilled in the art to which the invention pertains.

We claim:

1. A broadband circularly polarized antenna comprislng:

a rectangular channel cavity element defining an elongated rectangularly-shaped enclosed area, a plurality of monopole elements positioned on a wall of said cavity element in rectilinear array, said channel cavity having a ared portion outwardly diverging in the direction of wave propagation, and a polarized grid element overlying an outer end of said ared portion; a resistive card disposed within said ared portion, and lying in a plane parallel to the direction of wave propagation.

2. A broadband circularly polarized antenna comprising:

ilared portion; said grid element including a plurality of planar gratings and a plurality of dielectric HERMAN KARL SAALBACH Primary Exammer separating members disposed between said gratings. 10 M. NUSSBAUM, Assistant Examiner 3. Structure in accordance with claim 2, including a resistive card disposed Within said ared portion, and ly- U.S. C1. X.R. ing in a plane parallel to the direction of wave propaga- 333 98. 343 776 `824 909 tion.