Methods and apparatus for determination of a filter center frequency

1. A method for calculating a center frequency and a bandwidth for a radar doppler filter, the center frequency and bandwidth calculated to provide radar performance over varying terrain and aircraft altitude, pitch, and roll by keeping a doppler swath centered in an antenna beam, said method comprising:

receiving an antenna mounting angle, a slant range, and velocity vectors in body coordinates;

calculating a range swath doppler velocity, and a track and phase swath bandwidth using the antenna mounting angle, slant range, and velocity vectors;

calculating a phase swath doppler velocity based at least in part on the range swath doppler velocity and the track and phase swath bandwidth;

calculating a range swath center frequency based on the range swath doppler velocity;

calculating a phase swath center frequency based on the phase swath doppler velocity; and

calculating a level and verify swath bandwidth based upon the track and phase swath bandwidth.

2. A method according to claim 1 wherein calculating a range swath doppler velocity comprises determining a doppler velocity, Vr at a range swath center frequency according to Vr=Vv×Cos(90−r−a)=Vv×Sin(a+r), where Vv=(Vx 2 +Vz 2 ) 0.5 , where Vx=velocity component on body x axis and Vz=velocity component on body z axis, a=ATan(Vz/Vx), and r is the antenna mounting angle.

3. A method according to claim 2 wherein calculating a range swath center frequency comprises determining a range swath center frequency, Fr, according to Fr=2×Vr/L, where L is a wavelength of the radar.

4. A method according to claim 3 wherein the wavelength, L, is 0.2291 feet.

5. A method according to claim 1 wherein calculating a phase swath doppler velocity comprises calculating a phase swath doppler velocity, Vp, according to Vp=Vv×Cos(90−(r−p)−a)=Vv×Sin(a+r−p), where Vv=(Vx 2 +Vz 2 ) 0.5 , where Vx=velocity component on body x axis and Vz=velocity component on body z axis, a=ATan(Vz/Vx), r is the antenna mounting angle, and p=(T×Vx/H)×(180/π) in degrees, where T=1/πB and is a delay through range swath filter, T×Vx is vehicle movement on body X axis, B is the swath bandwidth, and H is altitude in feet.

6. A method according to claim 5 wherein calculating a phase swath center frequency comprises determining a phase swath center frequency, Fp, according to Fp=2×Vp/L, where L is a wavelength of the radar.

7. A method according to claim 6 wherein the wavelength, L, is 0.2291 feet.

8. A method according to claim 1 wherein calculating a track and phase swath bandwidth, B, comprises:

setting a filter time constant equal to a time for travel across a swath; and

calculating filter bandwidth, B, according to B=Vx/(0.6(H) 0.5 ) in hertz, where Vx=velocity component on body x axis and H is altitude in feet.

9. A method according to claim 8 wherein level and verify swath bandwidth is calculated as a ratio of level and verify bandwidths to track and phase bandwidths, K, multiplied by track and phase swath bandwidth, B.

10. A processor configured to:

receive an antenna mounting angle, a slant range, and velocity vectors in body coordinates;

calculate a range swath doppler velocity, and a track and phase swath bandwidth using the antenna mounting angle, slant range, and velocity vectors;

calculate a phase swath doppler velocity based at least in part on the range swath doppler velocity and the track and phase swath bandwidth;

calculate a range swath center frequency based on the range swath doppler velocity;

calculate a phase swath center frequency based on the phase swath doppler velocity; and

calculate a level and verify swath bandwidth based upon the track and phase swath bandwidth.