Patent GB-1470253-A (GB)
Title: Doppler radar for continuous surveillance of a space area
IPC: G01S13/42
Filed: 1974-06-20
Abstract: 1470253 Radar INTERNATIONAL STANDARD ELECTRIC CORP 20 June 1974 [26 June 1973] 27427/74 Heading H4D A radar for the continuous surveillance of a spatial region comprises an aerial arrangement of a plurality of aligned aerial units, switching means for sequentially using said units for receiving, or transmitting, or both, the switching being such that the line of aerial units is scanned in one direction, and then in the other, a coherent receiver to which the received signals are applied and which provides output at a Doppler frequency, circuits for determining the two Doppler frequencies for each target which correspond, respectively, to the two directions of scanning of the aerial units, and circuits for computing the radial velocity and angular position of the target from the values of said Doppler frequencies. As described, a radar comprises a separate transmitting aerial 5, Fig. 8, with slotted waveguides fed by a transmitter 6 having a pulse modulator 7. A receiving aerial comprises aligned unit aerials S1 to S5, each constituted by slotted waveguides, the phase centres of the units being spaced a# apart (#= transmission wavelength, a=a constant factor). The aerial system may be rotated about a vertical axis for azimuthal scanning. The unit aerials S 1 to S5 are connected through respective pre-amplifiers 8 to 12 to the inputs of a switching unit 13, by which they are coupled sequentially to the input of a receiver 14, under the control of a clock CU. The output of the receiver is connected to one input of a phase detector 15. The modulator 7 is also controlled by the clock CU. A coherent oscillator 16 receives a part of the output of the transmitter 6, and applies a signal of reference phase to the other input of the phase detector 15. Outputs from the phase detector 15 and from the clock CU are applied to circuits 17 for determining in successive range slices the two Doppler frequency values Fdo+ Fd and Fdo - Fd, where Fdo = Doppler frequency due to radial motion of a target and Fd=Doppler frequency due to the radial component of the aerial scanning, which is positive for one direction of scanning, and is negative for the other. The two values are applied to computing circuits 18, which enable the values Fdo, Fd to be obtained, and hence the velocity v and elevation 0 of the target concerned. A feature of the invention is to improve accuracy by using the information obtained during several successive aerial scanning periods instead a single scanning period. To do this, spectral analysis of the received signal is necessary, and a suitable form of the circuitry 17 is shown in Fig. 9, using digital signal processing. In this, the phase detector 15 supplies two signals which are phase shifted by 90 degrees, thus enabling the sense of the radial velocity of the target to be determined. These signals are sampled and coded in range slices by circuits 20 and are then recorded by circuits 21 in one or other of two memories M1, M2 which are used alternately for writing and reading. Circuits 22 which read out from the memories provide range information, and inputs to a Fourier transform digital computer 24, one of said inputs being via a circuit 23 for determining values k1 for the orders of spectrum lines bracketing the Doppler frequencys. Outputs X1, X2 from the computer 24 are processed by logic circuits 25 to provide the values Fdo + Fd and Fdo - Fd.