Measurement techniques for input impedance, radiation pattern and conversion loss of a 90GHz quasi-optical annular slot receiver

In this paper, measurements of a 90 GHz annular slot lens receiver were performed. The measured input impedance, radiation pattern and conversion loss of the annular slot lens receiver was compared with FDTD simulations. Two designs were considered in which an extra matching stub was added to one of the designs to conjugate match the diode. The comparison of the impedance results between measurement and theory showed only a 5% shift in frequency and small deviations in absolute impedance value. The probable attributes to this small discrepancy might be the feed model in the FDTD simulation and the thin CPW probe. Measured radiation patterns for both co- and cross-polar patterns agree well with theory. The optimum conversion loss for the design without the matching stub is 17.4 dB with bias at 0.65 mA and LO power of -7.3 dBm while the optimum conversion loss for the design with the matching stub is 16.7 dB with bias at 0.36 mA and LO power of -7.5 dBm.