High prf unambiguous range radar

#1. Field of the Invention

#The invention relates to a pulse-compression-type MTI doppler radar system capable of operating at a high prf and not introducing range ambiguities. More particularly, the invention relates to apparatus for transmitting a train of pulses alternately coded with at least two codes, auto-correlating the target return of each coded pulse with pulse compressors matched to each code, and processing the pulse-compressed target returns with at least two MTI processing channels each of which will process target returns from one range segment of the operable radar range.

#2. Description of the Prior Art

#FIG. 1 is a block diagram representation of a pulse-compression MTI doppler radar system utilizing multiple waveform generators, pulse compressors, and MTI processing channels.

#FIG. 2 is a diagrammatic view of time versus distance plots showing the propagation of transmitted coded pulses at successive time intervals and their respective target return signals.

#A pulse-compression MTI doppler radar system utilizing multiple waveform generators, pulse compressors, and MTI processing channels to resolve range ambiguities is outlined in FIG. 1. A coded modulator 10 contains a conventional prf generator 12 connected to a multiplexer 14 containing switch 16 which provides pulses alternately through lines 18 and 20 to A and B waveform generators 22,24, respectively. In MTI doppler radar systems generally, the pulses are provided at a rate of 100 to 2000 pulses per second. A and B waveform generators 22,24 are of a standard type such as that described in "Radar Design Principles," by F. E. Nathanson (1969), pp 490,491, Chapter 3. A waveform generator 22 generates an A code pulse which has a low cross-correlation with a B code pulse generated by B waveform generator 24. A discussion of phase coded pulse-compression techniques and the selection of optimum coding is provided at pages 497 and 498 of "Introduction to Radar Systems" by Skolnik (1962). Although the invention for simplicity purposes is described as having two waveform generators, additional waveform generators up to a quantity designated as Z waveform generator 26 may be used.

#A and B waveform generators 22,24 are connected through lines 30 and 32, respectively, to multiplex switch 34 of multiplexer 36. Switch 34 is connected to transmitter 38 which is in turn connected through line 40 to antenna 42, containing duplexer 44 and reflector 46.

#Target return signals are received by antenna 42 which is connected through line 48 to receiver 50 which contains mixer 52, local oscillator 54, and IF amplifier 56. Transmitter 38, antenna 42, and receiver 50 are all conventional radar components such as described in "Introduction to Radar Systems" by Skolnik (1962), page 493. Amplifier 56 is connected through line 58 to A pulse compressor 60 and B pulse compressor 62 of pulse compression filter 64. A and B pulse compressors 60,62 are of a conventional type as described in "Radar Design Principles" by F. E. Nathanson (1969), page 320. A pulse compressor 60 is matched to A waveform generator 22 such that the A code pulse target returns autocorrelate optimally in A pulse compressor 60. In the same manner B pulse compressor 62 is matched to B waveform generator 24. Z pulse compressor 63 represents the additional pulse compressor(s) that would be required if the quantity of waveform generators designated Z waveform generator 26 were used. A and B pulse compressors 60,62 are connected via lines 66 and 68, respectively to MTI processor 70. Multiplexer 72 directs pulse compressed signals via switches 74 and 76 to either MTI processing channel (R.sub.0 -R.sub.1) 78 (hereinafter processing channel 78), or to MTI processing channel (R.sub.1 -R.sub.2) 80 (hereinafter processing channel 80). MTI processing channel R.sub.2 -R.sub.Z, 82, represents the additional channels in the system that would be used if more than two waveform generators and pulse compressors were used. R.sub.0 -R.sub.2 designates the operable range of the radar, with R.sub.0 -R.sub.1 representing the first half-segment of the operable range and R.sub.1 -R.sub.2 representing the second half-segment of the operable range. Multiplexer 72 directs all A and B code pulse-compressed signals from targets in the range R.sub.0 -R.sub.1 to processing channel 78. Similarly all A and B code pulse-compressed signals from targets in the range of R.sub.1 -R.sub.2 are directed to processing channel 80. To accomplish this, switches 74 and 76 change positions each time a prf pulse is generated by prf generator 12. Processing channels 78 and 80 calculate target range and speed information and pass it to display 84.