The use of digital modulation signals in radar system for detection of nonlinear scatterers

This paper deals with initial application of digital modulation techniques in the radar systems utilizing non-linear junction detection (NLJD) principle. Various types of devices, such as handheld detectors for searching of hidden listening devices, have previously been developed and are commercially available. However, these devices transmit single frequency harmonic waveform which in general limits efficiency of energy transmission to nonlinear scatterer. A novel method using wideband transmit signal with phase shift keying digital modulation was proposed and analyzed. A simple mathematical model of nonlinear scatterer´s response for modulation application was created and simulated in MATLAB. It was proved by experimental measurements that narrowband detection is achieved at the receiver with significant contribution to transmitter power efficiency compared to conventional single frequency pulse modulated CW systems. Significant performance gains and only modest increase in complexity of the transmitter make this method attractive for harmonic radar systems.