A Digital Correction Method for Increased Dynamic Range in Interferometric Six-Port Radars

In this letter, we demonstrate a digital correction method for extending the dynamic range of a six-port radar system based on detector diodes. An individual diode gain is considered to depend on output voltage, which can be approximated as a linear function in order to extrapolate the diode's square-law response to higher input powers. The individual diode coefficients are extracted during an initial calibration measurement utilizing the interferometric working principle. A six-port junction in combination with power detectors based on Si Schottky diodes operating at 24 GHz has been employed to validate the concept. Reduction of the third- and fifth-order harmonics of up to 35 and 22 dB, respectively, has been achieved at the highest input power of 8 dBm. The correction was applied for a wide range of operating conditions. As a result, the increase in phase error under large-signal and high power operation is effectively compensated and remains low under small-signal conditions. Thus, phase accuracy is maintained beyond the classical dynamic range of detector diodes in six-port applications so far.