Fully micromachined power combining module for millimeter-wave applications

A fully micromachined power combining module is demonstrated with an RF power efficiency of up to 25% at the output power of 72.2 GHz. In the module, the output signal of a GaAs MMIC frequency multiplier is coupled to a micromachined waveguide via a rectangular transition probe. The waveguide, micromachined in silicon using "split-block" technique, then can be used to feed a highly directive micromachined horn antenna and finally, a number of these modules can be combined together to constitute a fully micromachined waveguide-based power combining system for high-power millimeter-wave applications. When tested separately, GaAs MMIC frequency multipliers utilized in the demonstrated power combining module show an excellent RF power efficiency of up to 36.1% at the output power of 76.2 GHz. This is the highest efficiency reported for a diode-based MMIC multiplier with the output frequency in the W-band (75--110 GHz). In the power combining module, the output of this frequency multiplier is coupled to a micromachined waveguide via a transition probe that couples popular finite ground coplanar line to waveguides. Such a transition, when tested separately in the W-band, shows excellent return loss and insertion loss performance across the entire waveguide band. In addition, demonstrated free-standing probe proves the potential of such transitions to be applicable well into the submillimeter-wave and THz regime. The demonstrated module integrates, for the first time, two heterogeneous components, the compact GaAs MMIC frequency multipliers and silicon micromachined waveguide, through a unique micromachined arrangement. GaAs monolithic circuits provide optimum high frequency performance while silicon micromachined components allow low cost fabrication. In addition, the module efficiency can be improved further by wafer bonding the two waveguide halves and also by reducing the length of the 3000 mum long 50 O FGC line section between the multiplier output and the transition probe. Therefore, the proposed power combining system is a promising candidate for a low-cost and efficient power source for high-frequency high-power application sources.