Abstract: A tracking radar system comprising an aerial arrangement having a plurality of outputs, means for deriving from the aerial outputs a sum signal representative of the sum of the aerial outputs and a difference signal representative of the direction of a target relative to the aerial, a receiver for processing said sum and difference signals to produce corresponding intermediate frequency sum and difference signals, means for comparing the intermediate frequency sum signal with the output of an oscillator in a first phase-locked loop and using the resulting signal to control the oscillator frequency so as to cause the oscillator to lock on to the frequency of the intermediate frequency sum signal, a phase-sensitive detector for comparing the intermediate frequency difference signal with the output of the oscillator to produce an output signal representative of the phase difference between the sum and difference signals, and bandwidth alteration means responsive to the sum signal to alter the bandwidth of the fi

Abstract: A signal acquisition circuit for a missile guidance system has a phase lock loop which is responsive to incoming signals received from a target and will lock on to the frequency of the received signal. The bandwidth of the phase lock loop is altered in dependence on the signal being received in order to distinguish between a valid target and noise.