Misaligned Waveguide-Based Branch Waveguide Structure for Amplitude Imbalance Improvement in Branch-Guide Coupler

This study proposes a novel branch waveguide structure based on the misaligned waveguides (MWs). The design attains asymmetry by incorporating an offset within the branch waveguide, facilitating the excitation of the TE201 mode. Introducing the TE201 mode yields a transmission zero (TZ) that can significantly improve amplitude imbalance. The position of the TZ is related to the coupling strength of the TE201 mode, which can be flexibly controlled using the offsets. Furthermore, the proposed branch waveguide structure introduces only one additional design parameter compared to the conventional configuration and eliminates the need for extra chamfers, simplifying the design and fabrication processes. This distinct branch waveguide structure establishes the foundation for designing ultrawideband branch-guide couplers (BGCs) with low amplitude imbalance. We validate the design principles by designing, fabricating, and testing an eight-branch 3-dB BGC prototype operating in the
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-band. Measurements over 50–72 GHz (with a fractional bandwidth of 36%) demonstrate the amplitude and phase imbalances of less than 0.4 dB and 2.7°, respectively. In addition, the return loss and isolation exceed 20 dB, closely agreeing with simulations.