Planar Schottky diodes in submillimeter-wavelength waveguide receivers

This dissertation discusses the use of high frequency modeling techniques for the design of planar Schottky diode mixers at submillimeter wavelengths. The ultimate goal of this research was to better understand the effect of the planar diode geometry on mixer performance, and to determine how best to design the diode chip and mixer circuitry for optimum mixer performance. In particular, this research focused on the design and testing of a 585 GHz fundamentally-pumped fixed-tuned planar Schottky diode waveguide mixer. A system noise temperature of 2500 K(DSB) and a total system conversion loss of 8.6 dB(DSB) were measured at 585 GHz using less than 0.5 mW of local-oscillator power. This result represents the best planar diode mixer results in this frequency range. It is important to note that the 585 GHz planar diode mixer has no variable tuning elements, in contrast to the best whisker-contacted mixers, which used tunable backshorts. Hewlett Packard's High Frequency Structure Simulator, a three-dimensional finite-element analysis program, was used to determine the diode's embedding impedance mounted in the mixer circuit. The harmonic balance technique was used to predict the mixer performance at different embedding impedances. The results of these analyses were used to design the mixer circuitry and to determine the sensitivity of the mixer performance to changes in the diode chip geometry and mounting circuitry. A comparison was performed between the measured mixer results and the modeling, indicating that the modeling is useful in designing to near the optimum mixer operating point. In addition, the modeling and measurements indicate that with careful diode soldering the results obtained during this research can be readily reproduced.