Scale-model design of a submillimeter-wave planar diode mixer

The design of a planar diode submillimeter-wave mixer is presented in which scale models play an important role. By constructing larger scale models of mixer components, the design process is simplified by making component changes easier and by making the measurements easier with the aid of a network analyzer. Separate scale model measurements were used to find optimum diode geometry, a wide bandwidth transition from circular waveguide to shielded microstrip, a DC return bondwire, and a microstrip low-pass filter. After combining the results from these measurements to form a mixer circuit model, the combined effect of the various components was studied, and adjustments were made to present an optimum impedance to the diode terminals. Tests of the design at 345 GHz confirm the accuracy of the scale model design procedure. Design information presented on the different components will be useful for developing future planar diode mixers