BACKLOBE REDUCTION IN REFLECTOR-TYPE ANTENNAS

• US 3,599,219 A
• Filed: 01/29/1969
• Issued: 08/10/1971
• Est. Priority Date: 01/29/1969
• Status: Expired due to Term

• Current Assignee: N/A
• Original Assignee: N/A
• Time in Patent Office: 923 Days
• US Class Current: 343/840
• CPC Class Codes: H01Q 19/022 for reducing the edge scattering of reflectors

Abstract

The axial backlobe of a circular parabolic antenna dish is greatly reduced by providing variation of the phase of radiation diffracted at successive portions of the edge. The phase is varied by providing an edge configuration in which successive portions of the edge are at differing distances from the feed. A dual-polarized antenna employs a polygonal rim surrounding the round reflector. A large increase in front-to-back ratio is obtained. The theory of operation is described to enable use in other structures.

Claims

1. In microwave transmission apparatus including at least one feed radiator and a conducting reflector of predetermined reflecting surface shape having at least a portion of its boundary exposed to feed radiations of substantially equal phase, the improved construction characterized by having a conducting extension on at least a portion of the boundary of the reflector so exposed, the extension departing from the reflecting surface shape and having means thereon for producing, at remote rearward locations, diffracted radiation fields of progressively advanced and progressively retarded phase from successive points along the edge of the extension, each progression of relative phase including a plurality of phases intermediate between the most advanced and the most retarded, the difference between the latter phases being greater than 180*, the rearwardly diffracted energy being widely diffused in directionality by the interaction of the numerouS phases.

2. The improved microwave transmission apparatus of claim 1 wherein there are a plurality of such progressions, the phase produced at successive points being alternately advanced and retarded along the edge.

3. The improved microwave transmission apparatus of claim 1 having delay means varying the transmission time of radiations from the feed to successive portions of the edge to excite the diffracted radiation in differing phase.

4. The improved microwave transmission apparatus of claim 3 wherein the edge of the extension has successive portions at differing distances from the feed and constitutes the delay means varying the transmission time to the successive portions.

5. The improved microwave transmission apparatus of claim 4 wherein the edge of the extension has portions of alternatingly increasing and decreasing distance from the feed.

6. The improved microwave transmission apparatus of claim 4 wherein the difference between the greatest and smallest distance of any portions of the edge from the feed is between 1/2 wavelength and 3 wavelengths at the operating frequency of the feed.

7. The improved microwave transmission apparatus of claim 6 wherein the difference is approximately one wavelength.

8. The improved microwave transmission apparatus of claim 6 wherein the extension extends in a direction close to parallelism with the direction of the radiations from the feed incident thereon, so that the difference of linear distances from successive portions of the edge to the perimeter of the reflecting surface is substantially equal to the difference of distances of such portions of the edge from the feed.

9. The improved microwave transmission apparatus of claim 1 wherein the boundary of the reflector is circular and the feed radiations have their electric field linearly polarized across a diameter, the reflector having at least one such conducting extension on the portions in the region of each end of said diameter.

10. A suppressed-backlobe parabolic dish antenna comprising the improved microwave transmission apparatus of claim 9 wherein the reflector is a circular parabolic dish having the feed at the focus.

11. The parabolic dish antenna of claim 10 wherein the extensions on said portions comprise arcuate ring-segments of alternately increasing and decreasing radial dimension on the periphery of the dish aperture.

12. The parabolic dish antenna of claim 11 wherein the outer edge of at least a portion of each ring-segment is linear and substantially tangent to the circular aperture.

13. The parabolic dish antenna of claim 12 wherein each ring-segment has a plurality of such tangent linear edges forming a generally polygonal segment-edge shape.

14. The parabolic dish antenna of claim 11 wherein the maximum difference of distance of portions of the edges from the feed is from 1/2 wavelength to 3 wavelengths at the operating frequency.

15. The parabolic dish antenna of claim 14 wherein the feed is closely adjacent to the front plane of the dish and the extensions extend substantially wholly radially in that plane so that the difference in distance from the feed is substantially equal to the difference of radial extension.

16. The parabolic dish antenna of claim 15 having thereon an entire circular ring so formed.

17. The parabolic dish antenna of claim 16 wherein the outer edges of the ring are in the general form of a polygon circumscribed about the circular aperture.

18. The parabolic dish antenna of claim 17 wherein the ring has a maximum radial extension of approximately one wavelength, the maximum extension being at short flat regions at the vertices of the polygon.