GB935694A - Radar system - Google Patents

Abstract

935,694. Pulse radar; pulse modulation systems. STANDARD TELEPHONES & CABLES Ltd. (Nippon Electric Co. Ltd.). Dec. 18, 1959, No. 43092/59. Classes 40 (5) and 40 (7). In order to prevent jamming of a pulse radar the transmitted signal comprises recurrent groups of carrier-wave pulses, the pulses in each group being spaced in time according to a predetermined code and the phase of the carrier-wave being varied in time in accordance with a predetermined code, and the receiver includes a decoding circuit comprising means for delaying at least one portion of the received carrier-wave with respect to another by a time interval dependent on the spacing between the transmitted pulses and means for shifting the phase of the said one portion of the carrier - wave with respect to the other. As described, each pulse group comprises three pulses 1, 2, 3, Fig. 1. The time intervals # 1 , # 2 between pulses 1, 2 and 2, 3 are different, both # 1 and # 2 are integral multiples of the RF period and the RF phase of pulse 1 is opposite to that of pulses 2 and 3 as indicated by the hatching on the pulse 1. At the receiver the RF or IF echo pulses are applied to a decoder, Fig. 3, having input and output terminals 24, 30 and comprising two delay devices 25, 27 having delay times # 2 and # 1 respectively and a phase changer 29 which shifts the carrier phase by 180 degrees. Thus, each pulse reaches the output terminal 30 (1) directly, (2) with a delay # 2 , and (3) with a delay # 1 and # 2 , and a 180 degree phase shift. The resultant three components of each of the pulses 1, 2 and 3 are shown in Fig. 4 (a), (b) and (c) respectively, and it is seen that the third, second and first components of pulses 1, 2 and 3 respectively, combine to give a large amplitude pulse 34, Fig. 4 (d), which may be separated from the other components by an amplitude discriminator. In a superheterodyne receiver, Fig. 2 (not shown), the CW RF input to the transmitter modulator is obtained by heterodyning outputs from the local oscillator and an IF oscillator and selecting one sideband.