Image Number 3 for United States Patent #5109231.
A radar system comprises a transmitter which essentially continuously transmits a modulated carrier wave signal and a receiver for receiving the carrier wave signal reflected at an object (echo signal). The carrier wave signal is modulated with a code-generating signal whose code frequency is determined for the range resolution of the radar. The code-generating signal is such that one bit in the code has a duration which is several times longer than the period of the carrier wave signal and several bits of the code form a block which is obtained by modulation of a carrier wave with constant frequency. The frequency of the carrier wave is changed between blocks so that the transmitter sends a block with a carrier wave frequency which is different from the carrier wave frequency or frequencies which the receiver is set up to receive. The receiver stores the transmitted code and correlates it with the received signal. When code correspondence (synchronism) is obtained this corresponds to a definitive position of the echo response reflector. By changing frequency between blocks different "types of radar" can be dedicated to different range zones, and a radar system is obtained which is adapted to cope with modern threat environments. The radar is difficult to spot, difficult to define and to disturb.