RADAR

摘要

A tracking radar system (Figs 2 and 3 not shown) has a multi-element aerial (1). A receiver (10) processes radio-frequency sum (S) and difference (D) signals derived from the aerial to produce corresponding intermediate frequency sum (S<1>) and difference (D<1>) signals. The oscillator (62) of a phase-locked loop (60) locks on to the frequency of the intermediate frequency sum signal (S<1>), and a phase-sensitive detector (34) compares the oscillator (62) output with the intermediate frequency difference signal (D<1>) to produce an output signal representing the direction of a target relative to the aerial. The phase-locked loop includes a variable gain circuit (300). Responsive to the intermediate frequency sum signal (S<1>), a threshold detector (304) produces a first or second output signal. The first threshold output signal is combined with a target acquisition signal to cause the variable gain circuit (300) to slowly decrease the bandwidth of the phase-locked loop (60). The second threshold output signal causes the variable gain circuit (300) to rapidly increase the bandwidth of the phase-locked loop (60). The invention is particularly concerned with the use of sidebands added to the narrowband oscillator (62) output to simulate the sidebands in the wideband sum signal I.F. As shown the narrow band intermediate frequency sum signal from oscillator 62 is combined at 605 within the first phase locked loop with a proportion of the output of a second wide band phase locked loop 600-603 to provide pseudo sidebands of constant amplitude.