a scanning radar system suitable for detecting and monitoring ground - based targets includes a frequency generator , a frequency scanning antenna , and a receiver arranged to process signals received from a target so as to identify a doppler frequency associated with the target . the frequency generator generates sets of signals , each set having a different characteristic frequency , and includes a digital synthesiser arranged to modulate a continuous wave signal of a given characteristic frequency by a sequence of modulation patterns to generate one set of signals . the frequency scanning antenna cooperates with the frequency generator to transceive radiation over a region having an angular extent dependent on the generated frequencies . digital synthesiser techniques capable of precise frequency generation and control are combined with passive frequency scanning and doppler processing techniques , enabling accurate control of range and scan rates , and optimisation of range cell size for factors such as slow and fast target detection and signal to noise ratio , so that targets can be detected at distances considerably farther away than is possible with known systems having similar power requirements .