Detecting Nonlinear Junctions Using Harmonic Cross-Modulation

Cross-modulation produced by nonlinear junctions is described mathematically and captured experimentally. The effect is modeled by the same memory-less power series which predicts the generation of harmonics by electromagnetic nonlinearities. Nominal specifications for a single-transmitter harmonic detector are presented; that architecture is compared to one which splits the original broadcast-probe power between two transmitters and receives cross modulation. Assuming equal total transmit power, the system-generated distortion of the cross-modulation detector is lower than that of the harmonic detector, while the peak strength of the received target response is the same. Data collected on a variety of radio-frequency mixers, amplifiers, and antennas indicate that assemblies of such components may act as calibration targets for harmonic radars or similar nonlinear-junction detectors.