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A novel and compact millimeter-wave (mm-Wave) spatial power combiner is developed integrating a silicon-based integrated circuit (IC) in a metal waveguide (WG). As an initial step toward integrating a silicon-based active IC in a WG, a passive back-to-back (B2B) transition incorporating a four-way spatial power splitter and combiner is realized at $E$ -band (71–86 GHz). In contrast to existing solutions, the proposed design considers power splitting and combining using a low-loss wireless transition between the IC and the WG. The proposed B2B structure comprises an IC implemented using the Institute for High Performance Microelectronics (IHP’s) 0.13- $\mu \text{m}$ SiGe BiCMOS technology integrated into the $H$ -plane of a WG. The IC is postprocessed and assembled in the WG prototype. The measured prototype shows a return loss better than 13 dB, an average insertion loss of 1.7 dB for a single transition, and a fractional bandwidth of 26.4% (69–90 GHz).

A contactless transition from a high-permittivity microstrip line ( $\epsilon _{r}=9.9$ ) to an air-filled waveguide (WG) has been impedance-matched over a large simulated relative bandwidth of 38% ( $W$ -band, 75–110 GHz). The transition couples the electromagnetic fields directly from the Monolithic Microwave Integrated Circuit (MMIC’s) microstrip line via an Substrate Integrated Waveguide and an off-chip stub section to a ridge WG section. The novel structure is low loss and suits pick-and-place assembly techniques of mm-wave MMICs inside metal WGs. The design process is detailed and manufacturing tolerances of the alumina prototype printed circuit board are discussed. The measured back-to-back structure retains an appreciable insertion loss smaller than 0.8 dB for a single transition and a fractional bandwidth of 28% (72–95 GHz) over which the return loss is greater than 10 dB.