| 摘要 |
1,140,590. Pulse radar. STANDARD TELEPHONES & CABLES Ltd. 22 Dec., 1966 [27 Dec., 1965], No. 57377/66. Addition to 1,073,024. Heading H4D. [Also in Division G1] A system for generating a clear correlation signal free of sidebands for use in a pulse radar operates by transmitting either in time or frequency multiplex two sequences of coded pulses, each in a different code. The received replies of the sequences pass to a correlator which also receives delayed versions of the transmitted sequences. Corresponding sequences in the received and delayed signals are individually correlated at different delays, and the two correlation results so obtained are themselves correlated. A clear unambiguous correlation signal is then obtained at only one value of delay. In a time multiplex arrangement (Fig. 1) sequences S 1 (t), S 2 (t) modulating a carrier derived at 8 are derived from pulses from a generator 5 and codes 7, 10, the particular sequence transmitted being determined by counter 9 and gate 6. The sequences are combined at 11, amplified and transmitted. They are also passed via a variable delay unit 12 to corresponding multipliers 16, 17. In these the separate sequences are multiplied with the received signals obtained at 4 and integrated to obtain the correlation waveforms for each sequence. The waveforms contain a large spike indicating true correlation and several smaller spikes. The two waveforms are themselves correlated in units 20 and 21. The codes used in the sequences are so chosen that this second correlation step will result in only a single clearly defined output pulse. In an alternative embodiment (Fig. 2, not shown) the two sequences of coded pulses are modulated on different carrier frequencies, which are mixed before transmission to achieve frequency multiplexing. At the receiver the two frequencies are separated by filtering before carrying out correlation. Details of suitable codes are described and illustrated in the specification. |
