Circularly polarized automotive radar for improved signal to noise ratio

1. A sensor assembly for detecting an object comprising:

at least one radar transmitter configured to emit transmitted radar waves having a first polarization, the at least one radar transmitter including a plurality of transmit encoding switches each coupled to one of a plurality of radar transmit antennas, each of the plurality of radar transmit antennas is configured to transmit the transmitted radar waves with a different respective polarization than another one of the plurality of radar transmit antennas;

at least one radar receiver configured to:

receive the transmitted radar waves after reflecting from the object as reflected radar waves having a second polarization different than the first polarization and corresponding with a detection of the object relative to the sensor assembly, and

reject radar waves having a polarization being different than the second polarization to disregard noise generated by environmental interaction of the transmitted radar waves and from extraneous radar sources;

the at least one radar receiver including a plurality of receive decoding switches each coupled to one of a plurality of radar receive antennas, each of the plurality of radar receive antennas is configured to receive the reflected radar waves with the different respective polarization; and

a sensor microprocessor configured to:

control emission of the transmitted radar waves using the at least one radar transmitter,

control the plurality of transmit encoding switches to modulate a radar signature comprised of sequential transmissions by each of the plurality of radar transmit antennas with the different respective polarization,

control the plurality of receive decoding switches to receive the reflected radar signature, and

detect of the object relative to the sensor assembly using the at least one radar receiver.

2. The sensor assembly as set forth in claim 1 , wherein the at least one radar receiver is configured to accept the radar waves having a polarization having the second polarization for the detection of the object generated by interaction of the transmitted radar waves with the object causing an alteration in the first polarization of the transmitted radar waves.

3. The sensor assembly as set forth in claim 1 , further including a sensor printed circuit board and wherein the at least one radar transmitter and the at least one radar receiver are disposed on the sensor printed circuit board and electrically connected thereto, wherein the at least one radar transmitter includes at least one polarized transmit antenna configured to generate the transmitted radar waves having a circular polarization of a first direction and the at least one radar receiver includes at least one polarized receive antenna configured to receive the reflected radar waves having a circular polarization of a second direction.

4. The sensor assembly as set forth in claim 1 , wherein the first polarization is a linear polarization and the sensor assembly further includes a filter cover disposed adjacent to and covering the at least one radar transmitter and configured to circularly polarize the transmitted radar waves.

5. The sensor assembly as set forth in claim 3 , wherein the circular polarization of a first direction is one of a right-handed polarization and a left-handed polarization and the circular polarization of the second direction is the other one of the right-handed polarization and the left-handed polarization.

6. The sensor assembly as set forth in claim 1 , wherein the at least one radar transmitter includes a plurality of radar transmit antennas electrically coupled to the sensor microprocessor and the at least one radar receiver includes a plurality of radar receive antennas electrically coupled to the sensor microprocessor, and wherein each of the plurality of radar transmit antennas and each of the plurality of radar receive antennas comprise a patch antenna having a rectangular shape including a pair of longitudinal sides of a first length being parallel and spaced from one another and a pair of lateral sides of a second length a being parallel and spaced from one another and extending between the pair of longitudinal sides and a first feed and a second feed for each coupling to one of a pair of excitation lines.

7. The sensor assembly as set forth in claim 6 , wherein the patch antenna defines a pair of truncated corners disposed diagonally opposite one another.

8. The sensor assembly as set forth in claim 6 , wherein the patch antenna defines a plurality of perturbations formed as at least one longitudinal notch along each of the pair of longitudinal sides and a plurality of lateral notches along each of the pair of lateral sides.

9. The sensor assembly as set forth in claim 6 , wherein the patch antenna defines a rectangular slot extending therethrough and diagonally across the patch antenna.

10. The sensor assembly as set forth in claim 6 , further including a feed network configured to electrically couple to the first feed and the second feed.

11. The sensor assembly as set forth in claim 10 , wherein the feed network comprises one of a hybrid coupler coupled to the first feed and the second feed and an offset coupler coupled to the first feed and the second feed.

12. The sensor assembly as set forth in claim 1 , wherein the plurality of radar transmit antennas includes at least one linearly polarized transmit antenna and at least one left hand circularly polarized antenna and at least one right hand circularly polarized antenna and the plurality of radar receive antennas includes at least one linearly polarized transmit antenna and at least one left hand circularly polarized antenna and at least one right hand circularly polarized antenna.

13. The sensor assembly as set forth in claim 1 , wherein the sensor assembly is electrically coupled to an object detection system for controlling a vehicle function with the detection of the object relative to the sensor assembly.

14. A method of operating a sensor assembly for detecting an object comprising the steps of:

emitting transmitted radar waves having a first polarization using at least one radar transmitter including a plurality of transmit encoding switches each coupled to one of a plurality of radar transmit antennas each configured to transmit the transmitted radar waves with a different respective polarization than another one of the plurality of radar transmit antennas;

controlling the plurality of transmit encoding switches to modulate a radar signature comprised of sequential transmissions by each of the plurality of radar transmit antennas;

receiving the transmitted radar waves after reflecting from the object as reflected radar waves having a second polarization different than the first polarization and corresponding with a detection of the object relative to the sensor assembly using at least one radar receiver including a plurality of receive decoding switches each coupled to one of a plurality of radar receive antennas each configured to receive the reflected radar waves with the different respective polarization;

rejecting radar waves having a polarization being different than the second polarization to disregard noise generated by environmental interaction of the transmitted radar waves and from extraneous radar sources using the at least one radar receiver;

controlling the plurality of receive decoding switches to receive the reflected radar signature; and

detecting the object relative to the sensor assembly using the at least one radar receiver.

15. The method as set forth in claim 14 , wherein the second polarization is an inverted form of the first polarization.

16. The method as set forth in claim 14 , wherein the first polarization of the transmitted radar waves is one of a left hand circular polarization and a right hand circular polarization and the second polarization of the reflected radar waves is the other one of the left hand circular polarization and the right hand circular polarization.