GB1319002A - Radar systems - Google Patents

Abstract

1319002 Pulse radar; aerials MARCONI CO Ltd 23 Feb 1972 [1 May 1971] 12570/71 Headings H4A and H4D A within-pulse scanning radar system has a transmission aerial arrangement providing a fan-shaped beam which scans in elevation such that its movement is slower at low than at high elevations. As described, a vertical array of horns T 1 to T 2 , Fig. 2, provides a beam which is narrow in a vertical plane (e.g., 1À2 degrees between half-power points) but which has an azimuthal angle equal to the surveillance angle required. A transmission pulse generation circuit TG coupled to a master oscillator MO feeds pulses to the aerial elements T 1 to T 2 via a scanning arrangement ST, which introduces equal increments of phase change between said elements in accordance with the desired scanning rate. A receiving aerial arrangement comprises a horizontal array of horns A 1 to A n which provides a beam which is narrow in azimuth but which extends in elevation over the surveillance angle required. Each aerial element A 1 to A n is associated with a respective amplifier/frequency changing mixer F 1 to F n which has a second input from a respective local oscillator LO 1 to LO n controlled by the master oscillator MO. Within pulse scanning is effected by providing a progressive frequency difference of 1/t between successive local oscillators, where t is the pulse duration (e.g., 2À5 micro-seconds). Thus, if the frequency of the local oscillator associated with the central aerial element is f 0 , those of the local oscillators for the elements on either side would be f 0 + 1/t, for the next pair f 0 + 2/t, and so on. Each unit F 1 to F n feeds into a respective storage filter S 1 to S n having a bandwidth of 1/t and connected to a utilization line U. Both range and direction are determined in quantized form. As shown in Fig. 3, the transmission beam may be scanned from maximum elevation to zero elevation in steps having decreasing speeds and pulse repetition frequencies (P.R.Fs.) and with maximum dwell at the end of the scan. The beam may be stepped back by a beamwidth at each change of P.R.F., it being arranged that signals received during these steps are ignored by the processing equipment. Instead of stepping back the scanning, Gaussian loading of the receiver sensitivity may be employed at each change of P.R.F.