Two-band microwave antenna with nested horns for feeding a sub and main reflector

• US 4,489,331 A
• Filed: 01/21/1982
• Issued: 12/18/1984
• Est. Priority Date: 01/23/1981
• Status: Expired due to Fees

• Current Assignee: Thomson-CSF (Thales SA)
• Original Assignee: Thomson-CSF (Thales SA)
• Inventors: Bouko, Jean, Salvat, Francois, Coquio, Claude
• Primary Examiner(s): Lieberman, Eli
• Assistant Examiner(s): Wimer, Michael C.
• Application Number:
  US06/341,580
• Time in Patent Office: 1,062 Days
• Field of Search: 343/781 P, 343/781 CA, 343/756, 343/776, 343/778, 343/786, 343/753, 343/755, 343/772, 343/779, 343/781 R, 343/777
• US Class Current: 343/753
• CPC Class Codes: H01Q 25/04 Multimode antennas corrugated horns H01Q13/0208
• CPC Class Codes: H01Q 5/45 using two or more feeds in association with a common reflecting, diffracting or refracting device

Abstract

A two-band multimode microwave source for an antenna of a low-elevation-tracking radar comprises a higher-frequency section nested in a lower-frequency section, the two sections having E-planes perpendicular to each other. The lower-frequency section includes two outer pairs of waveguides separated by a block which convergingly projects beyond their output ends and is bisected by the E-plane of that section. The higher-frequency section includes two inner pairs of waveguides disposed within that block and separated by an obstruction lying in the last-mentioned E-plane. The higher-frequency wave emitted by the inner waveguides is made planar by a lens disposed at n output aperture of the structure which is transparent to the lower-frequency wave. In a Cassegrain-type radar antenna the lower-frequency wave emitted by the source is returned by a semitransparent intermediate reflector toward a main reflector provided with a grid which rotates its plane of polarization to let it pass out through the intermediate reflector along with the higher-frequency wave which, passing unattenuated through the intermediate reflector, is returned by a solid outlying reflector to the main reflector.

Claims

1. A two-band multimode microwave source for the simultaneous radiation of waves in a lower-frequency band and in a higher-frequency band, comprising a waveguide structure forming a first cavity of rectangular cross-section and including two first pairs of waveguides which terminate at a discontinuity plane and are separated from each other by a first block projecting convergingly beyond said discontinuity plane into said first cavity, said first pairs of waveguides emitting into said first cavity a lower-frequency first wave, said first block being hollow and containing two second pairs of waveguides separated by a second block, said first block forming a second cavity communicating with said second pairs of waveguides and opening into said first cavity for emitting a higher-frequency second wave into the latter, said first cavity having an output aperture spaced from said second cavity in the direction of wave propagation for radiating both said first and second waves.

2. A microwave source as defined in claim 1 wherein said first pairs of waveguides and said first block have an orientation perpendicular to that of said second pairs of waveguides and said second block, said first and second waves having mutually perpendicular E-planes respectively bisecting said second and said first block.

3. A microwave source as defined in claim 1 or 2 wherein said first cavity terminates in a flared-out first horn defining said output aperture, said second cavity forming a flared-out second horn terminating at a further plane.

4. A microwave source as defined in claim 3, further comprising a metallic lens at said output aperture focusing said second wave into an outgoing beam with planar wavefront.

5. A microwave source as defined in claim 4 wherein said first and second waves have mutually perpendicular E-planes, said lens consisting of metal strips paralleling the E-plane of said second wave for letting said first wave pass through substantially unaltered.

6. A microwave source as defined in claim 5 wherein said output aperture is separated from said further plane by a distance which is smaller than the extent of a Rayleigh zone of said second wave in the direction of propagation.

7. A microwave source as defined in claim 6 wherein said second and first waves have frequencies related to each other in a ratio of at least 10:

1.

8. A radar antenna adapted to radiate waves in a lower-frequency band and in a higher-frequency band, comprising:

a waveguide structure forming a first cavity of rectangular cross-section and including two first pairs of waveguides which terminate at a discontinuity plane and are separated from each other by a first block projecting convergingly beyond said discontinuity plane into said first cavity, said first pairs of waveguides emitting into said first cavity a lower-frequency first wave, said first block being hollow and containing two second pairs of waveguides separated by a second block, said first block forming a second cavity communicating with said second pairs of waveguides and opening into said first cavity for emitting a higher-frequency second wave into the latter with a plane of polarization perpendicular to that of said first wave, said first cavity having an output aperture spaced from said second cavity in the direction of wave propagation for radiating both said first and second waves;

a forwardly concave main reflector centered on said waveguide structure;

a rearwardly convex intermediate reflector forwardly of said main reflector, said intermediate reflector being transparent to said second wave while directing said first wave back onto said main reflector;

a rearwardly convex outside reflector forwardly of said intermediate reflector sending back said second wave substantially unaltered through said intermediate reflector to said main reflector; and

a polarization-rotating grid adjacent said main reflector for making the polarization of said first wave codirectional with that of said second wave and enabling both said waves to be redirected forward by said main reflector via said intermediate reflector and past said outside reflector.