# US 4,400,701 A · Common antenna for primary and secondary radar

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- Number: US 4,400,701 A
- Document ID: US4400701A
- Status: Granted
- Kind: A
- Application number: 06/227,770
- Filed: 1981-01-23
- Granted: 1983-08-23
- Earliest claimed: 1980-01-28
- Assignees: Thomson-CSF
- Inventors: Albert Dupressoir
- Web page: https://patentgrep.com/patent/US4400701A

## CPC

- H01Q 21/28: Combinations of substantially independent non-interacting antenna units or systems {(multiple beam H01Q25/00)}
- H01Q 9/27: Spiral antennas
- H01Q 21/067: {using endfire radiating aerial units transverse to the plane of the array}
- H01Q 25/00: Antennas or antenna systems providing at least two radiating patterns (arrangements for changing or varying the orientation or the shape of the directional pattern H01Q3/00)
- Y10S 430/165: Thermal imaging composition
- H01Q: ANTENNAS, i.e. RADIO AERIALS (radiators or antennas for microwave heating H05B6/72)
- Y10S: TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS

## Abstract

A bifunctional antenna of a primary/secondary radar system comprises a reflector having a concave front surface illuminated by a source of primary radiation and formed with a row of circular ports along a horizontal generatrix, the ports lying forwardly of respective cavities or waveguides of cylindrical configuration excitable to emit circularly polarized secondary radiation. In some embodiments the polarization may be changed to a linear or an elliptical mode under the control of inserts rotatable about the cavity axis.

## Claims

### Claim 1

A bifunctional antenna for a primary/secondary radar system, comprising:
a reflector formed of a body of dielectric material with a reflective surface of crossed wires, said reflector being adapted to be illuminated by a primary source of outgoing radiation for detecting a remote target;
a row of emitters of secondary radiation disposed along a generatrix of said front surface intersecting a boresight axis, said emitters being formed by circular ports in said front surface backed by cylindrical cavities having walls integral with said body, said cavities being coaxial with said ports and having axes extending in radial directions of said front surface; and
wave-control means in said cavities adapted to establish a circular mode of polarization for the secondary radiation emitted thereby.

### Claim 2 (depends on 1)

An antenna as defined in claim 1 wherein said wave-control means comprises an insert in each cavity rotatable about said axis thereof for selectively changing said circular mode of polarization to a different mode.

### Claim 3 (depends on 2)

An antenna as defined in claim 2 wherein said emitters each include a linear exciter extending radially into said cavity at a location set back from said port thereof, said insert being located between said exciter and said front surface.

### Claim 4 (depends on 3)

An antenna as defined in claim 3 wherein said insert is disposed within said port.

### Claim 5 (depends on 3)

An antenna as defined in claim 3 wherein said insert comprises a planar grid of parallel conductors.

### Claim 6 (depends on 3)

An antenna as defined in claim 3 wherein said insert is a flat dielectric plate centered on said axis.

### Claim 7 (depends on 6)

An antenna as defined in claim 6 wherein said plate is substantially H-shaped.

### Claim 8 (depends on 1)

An antenna as defined in claim 1 wherein said wave-control means comprises an excitation element in each cavity coiled about the axis thereof.

### Claim 9 (depends on 8)

An antenna as defined in claim 8 wherein said excitation element is a helix tapering toward said port.

### Claim 10 (depends on 8)

An antenna as defined in claim 8 wherein said excitation element is a spiral located in said port at the front of each cavity.

### Claim 11 (depends on 1)

An antenna as defined in claim 1 wherein said cavities are dimensioned to establish a short-circuit plane at said front surface.