Detection of power lines was and remains to one of the major problems for helicopter radars at low-level flight, thus the basic difficulty is made by their detection against strongly reflecting spreading surface (makes wood, a dense bush, etc.). Calculations show that in the present state of affairs the probability of detection of an obstacle practically does not depend on distance, and is defined only by antenna beam width on an azimuth and the range resolution. As the beam width is limited by the admissible physical sizes of the antenna the range resolution 0.2 … 0.3 m that corresponds systems bandwidth 500 … 750 MHz, hence, should be provided.
To obtain such resolution it is possible three ways: use of short radio impulses (with carrying or without it), application of wideband signals (for example, signals with phase-code manipulation or chirp signals) and technicians of their compression or synthesis of necessary spectrum width of a signal for some periods of pulses repetition. Each of methods has advantages and lacks.
As have shown the conducted researches, for the decision of a task in view it is the most convenient to use the frequency-manipulated signals with pulse to pulse shifting of carrying and their subsequent coherent processing. The given way allows obtaining high range resolution in usual "narrowband" radar without a presentation of essential requirements to equipment. For this purpose it is necessary to provide only a corresponding mode of transmitting and operative changing of waveform in wide enough range of frequencies. High security of radar from aim hindrances on frequency, and also an effective utilization of a radio-frequency range can be thus provided.