Phased Array Antenna Using Stacked Beams in Elevation and Azimuth

• US 20160054439A1
• Filed: 08/20/2015
• Published: 02/25/2016
• Est. Priority Date: 08/21/2014
• Status: Active Grant

• Current Assignee: Raytheon Company (Rtx Corporation)
• Original Assignee: Raytheon Company (Rtx Corporation)
• Inventors: Brookner, Eli, Sikina, Thomas V., Drake, Peter R., Lok, Yuchoi F., Bourgeois, Jacqueline M., Rypysc, Daniel F., Chang, Yueh-Chi, Hartwich, Francis, Green, Leon
• Granted Patent: US 10,281,571 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G01S 13/42 Simultaneous measurement of distance and other co-ordinates indirect measurement G01S13/46
• CPC Class Codes: G01S 13/91 for traffic control G01S13/93 takes precedence
• CPC Class Codes: G01S 13/95 for meteorological use
• CPC Class Codes: G01S 7/024 using polarisation effects in waveguides H01P1/165; for aerials H01Q, e.g. H01Q15/22, H01Q15/24, H01Q19/195
• CPC Class Codes: H01Q 13/20 Non-resonant leaky-waveguide or transmission-line antennas; Equivalent structures causing radiation along the transmission path of a guided wave
• CPC Class Codes: H01Q 25/005 providing two patterns of opposite direction; back to back antennas H01Q25/004 takes precedence
• CPC Class Codes: H01Q 3/02 using mechanical movement of antenna or antenna system as a whole
• CPC Class Codes: H01Q 3/22 varying the orientation in accordance with variation of frequency of radiated wave
• CPC Class Codes: H01Q 3/38 the phase-shifters being digital
• CPC Class Codes: Y02A 90/10 Information and communication technologies [ICT] supporting adaptation to climate change, e.g. for weather forecasting or climate simulation

Abstract

A radar system uses a rotating antenna array having rows that display dispersive properties while feeding multiple radiating elements. In some embodiments, the radiating elements are dual polarized. In at least one embodiment, beam spoiling may be used to generate an unfocused transmit beam that covers an entire elevation range of interest. Digital beam forming may be used during a receive mode to achieve a stack of narrow-width receive beams in elevation. Frequency scanning may also be used to achieve stacked beams in azimuth.

Claims

1. A radio frequency (RF) system comprising:

an array antenna having a plurality of rows of radiating elements, wherein at least some of the rows have dispersive qualities that allow frequency scanning to be used with the row;

a motor to rotate the array antenna about an axis;

a plurality of transmit/receive (T/R) modules coupled to rows of the array antenna, the plurality of T/R modules including at least a first T/R module coupled to a port of a first row of the array antenna and a second T/R module coupled to a port of a second row of the array antenna; and

one or more digital processors coupled to the plurality of T/R modules to generate waveforms to be transmitted from the array antenna and to process return signals received by the array antenna, the one or more processors configured to;

generate a recurring radar waveform having at least a transmit portion and a receive portion, the transmit portion having multiple successive pulses at different RF frequencies to cause transmit beams to be generated by the array antenna at different azimuth angles, the recurring radar waveform having a pulse repetition frequency (PRF);

process return signals associated with the recurring radar waveform using digital beam forming (DBF) to generate a stack of narrow receive beams in elevation; and

process data associated with the stack of narrow receive beams using maximum likelihood estimation (MLE) to estimate target elevation and azimuth angles.

2. The RF system of claim 1, wherein the one or more processors are configured to:

generate multiple successive radar waveforms at a first pulse repetition frequency (PRF) to form a first coherent processing interval (CPI);

generate multiple successive radar waveforms at a second PRF to form a second CPI, the second PRF being different from the first PRF; and

process return data received during at least the first and second CPIs using MLE to generate an estimate of target azimuth angle, wherein the different PRFs associated with the first and second CPIs are used to reduce Doppler ambiguity. The second CPI could have a different carrier for frequency diversity.

3. The RF system of claim 2, wherein the one or more processors are configured to:

generate multiple successive radar waveforms at a third PRF to form a third CPI, the third PRF being different from the first and second PRFs; and

process return data received during at least the first, second, and third CPIs using MLE to generate an estimate of target azimuth angle, wherein the different PRFs associated with the first, second, and third CPIs are used to reduce Doppler ambiguity. The third CPI could have possibly a different carrier frequency from those of the first two CPIs for frequency diversity. There could be more than 3 CPIs.

4. The RF system of claim 2, wherein:

the number of successive radar waveforms generated for each PRF is based at least in part on the dwell time of the radar, antenna rotation rate, the azimuth beamwidth, and the carrier frequencies use for the CPIs.

5. The system of claim 1, wherein:

the one or more digital processors are configured to process return data associated with the transmit beams at different azimuth angles using MLE to generate an estimate of target azimuth angle.

6. The system of claim 1, wherein:

the first row of the array antenna includes dual polarized radiating elements, the first row having a first port associated with a first polarization direction and a second port associated with a second, orthogonal polarization direction.

7. The system of claim 6, wherein:

the plurality of T/R modules includes a first T/R module that includes a first port coupled to the first port of the first row of the array antenna and a second port coupled to the second port of the first row of the array antenna.

8. The system of claim 1, wherein the one or more digital processors are configured to:

generate the recurring radar waveform to include a first pulse at a first RF frequency that causes a first transmit beam to be generated by the array antenna at a first azimuth angle and a second pulse at a second RF frequency that causes a second transmit beam to be generated by the array antenna at a second azimuth angle; and

change the pulse repetition frequency of the recurring radar waveform based, at least in part, on a dwell time associated with the array antenna.

9. The system of claim 1, wherein the one or more digital processors are configured to:

generate the recurring radar waveform to include a first plurality of transmit pulses associated with a first radar application and a second plurality of transmit pulses associated with a second radar application that is different from the first radar application.

10. The system of claim 9, wherein:

the transmit pulses of the first and second plurality of transmit pulses each have a different RF frequency, wherein the one or more digital processors are configured to transmit the transmit pulses of the first and second plurality of transmit pulses using the same polarization.

11. The system of claim 9, wherein the one or more digital processors are configured to transmit the transmit pulses of the first plurality of transmit pulses at a different polarization than the transmit pulses of the second plurality of transmit pulses.

12. The system of claim 11, wherein the one or more digital processors are configured to transmit the transmit pulses of the first plurality of transmit pulses at a slant left polarization and the transmit pulses of the second plurality of transmit pulses at a slant right polarization.

13. The system of claim 9, wherein:

the first radar application is an air traffic control application and the second radar application is a weather radar application.

14. The system of claim 1, wherein:

multiple rows of the array antenna include dual polarized radiating elements and corresponding T/R modules have separate channels for horizontal and vertical polarization, wherein the separate channels for horizontal and vertical polarization each have a variable phase shifter that is controllable by the one or more digital processors.

15. A method of operating a radar system having a rotating array antenna that includes a plurality of rows of radiating elements, wherein at least some of the rows display dispersive properties, the method comprising:

transmitting multiple pulses during a transmit portion of a pulse repetition interval (PRI) from the array antenna, each of the multiple pulses having a different RF frequency to form a transmit beam at a different azimuth angle from the other pulses, wherein transmitting multiple pulses includes transmitting each of the multiple pulses using beam spoiling to achieve a transmit beam that covers an elevation angle range of interest;

processing return signals using digital beam forming (DBF) to develop a plurality of relatively narrow receive beams in elevation; and

processing data associated with the plurality of relatively narrow receive beams in elevation using maximum likelihood estimation (MLE) to estimate a target elevation angle.

16. The method of claim 15, further comprising:

processing return data associated with transmit beams at different azimuth angles using MLE to estimate a target azimuth angle.

17. The method of claim 16, wherein:

processing return data associated with transmit beams at different azimuth angles using MLE includes processing return data associated with transmit beams at different azimuth angles for multiple successive coherent processing intervals (CPIs), each of the multiple successive CPIs using a different pulse repetition frequency.

18. The method of claim 15, wherein:

transmitting multiple pulses during a transmit portion of a pulse repetition interval (PRI) from the array antenna includes transmitting a first plurality of pulses associated with a first radar application and transmitting a second plurality of pulses associated with a second radar application, wherein the first plurality of pulses use different RF frequencies than the second plurality of pulses.

19. The method of claim 15, wherein:

transmitting multiple pulses during a transmit portion of a pulse repetition interval (PRI) from the array antenna includes transmitting a first plurality of pulses associated with a first radar application and transmitting a second plurality of pulses associated with a second radar application, wherein the first plurality of pulses are transmitted at an orthogonal polarization with respect to the second plurality of pulses.

20. The method of claim 15, further comprising:

transmitting N successive PRIs at a first pulse repetition frequency (PRF) corresponding to a first coherent processing interval (CPI);

transmitting N successive PRIs at a second pulse repetition frequency (PRF) corresponding to a second CPI; and

transmitting N successive PRIs at a third pulse repetition frequency (PRF) corresponding to a third CPI;

wherein N is a positive integer greater than 2.

21. A method, comprising:

operating a radar having an antenna with rows of frequency scannable dispersive elements, wherein each of the rows has phase control such that phase scanning is provided in an angle orthogonal to the frequency scan for providing a two-dimensional scan using only one phase shifter and/or T/R module per row.

22. The method according to claim 21, further including providing element rotation about an axis perpendicular to the rows of dispersive elements for providing 360°

coverage.

23. The method according to claim 21, further including using the antenna split in two halves about the axis perpendicular to the antenna element axis;

and using a first half of the antenna for transmit and a second half for receive.