On-Chip Integrated Backshort for Relaxation of Machining Accuracy Requirements in Frequency Multipliers

Performance of a GaAs Schottky diode monolithic microwave integrated circuit (MMIC) with an integrated waveguide backshort septum, comprising a 1-2-μm-thick freestanding metal frame, is reported. The E-plane backshort metal establishes a short circuit in the waveguide away from the machined end wall. By defining the effective end of the waveguide using the metal frame, the dependence of the multiplier performance on very high tolerance machining, in this case the output waveguide backshort position, is reduced. A frequency doubler design at 186 GHz exploiting this approach is described-with a peak efficiency of 40%, the doubler generates ~100 mW for 250 mW of input power. Analyses show that the achieved performance is independent of possible inaccuracies in machining of the output waveguide and assembly of the MMIC.