Calibration procedures for microwave vector comparators

Abstract

This paper presents two calibration procedures for microwave vector comparators. The first is intended for architectures composed of a quadrature demodulator. It assumes that the output voltages of this component are expressed as cosine and sine functions with different amplitudes and DC offsets. Tests with a prototype using an ADL5380 have shown amplitude and phase errors less than 0.1 dB and 4.3°, respectively. The second calibration procedure is developed for comparators comprised of gain and phase detectors. A prototype with two AD8302 was designed to provide 360° phase coverage, since the AD8302 is limited to 180° phase detection. As the developed comparator couples the input signals internally, we introduce an efficient way of determining the corresponding coupling coefficients to ensure high accuracy. Tests with the prototype have shown amplitude and phase errors below 0.7 dB and 2°, respectively. Finally, experiments conducted in an anechoic chamber with a phased array and a direction finding system using the two prototypes demonstrate the efficacy of the calibration procedures.