This paper presents the design of a compact size, passive, W to K band subharmonic mixer with post-wall waveguide (substrate integrated waveguide) RF input interface. The mixer is based on a silica-glass structure where the post-wall waveguide and microstrip line are on separate substrates. This configuration maximizes the performance as the substrate thicknesses can be separately optimized for the lowest loss and mono-mode operation. Integration of different types of guiding structures also allows realization of e.g. millimetre-wave waveguide filters and microstrip circuits in a single structure, while preserving low-cost, low-weight and compact size. Furthermore, post-wall waveguides can be easily interfaced with conventional rectangular waveguides, as demonstrated in the paper, which simplifies millimeter-wave circuit packaging and eventual system integration. Design methodology of the mixer and transition circuits as well as measurements are presented. Minimum conversion loss of 19.6 dB was achieved at 86 GHz with 13.7 dBm/32.4 GHz LO signal. The presented design would be suitable for the future W-band cellular, radar or satellite communication systems.
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