A Sub-THz Waveguide Magic-T With Coplanar Ports for Power Combination Applications

Abstract

In this article, a compact waveguide magic-T (WMT) with four coplanar ports is presented for sub-THz power combination applications. In the WMT, simple and robust geometries, i.e. trapezoidal irises, cuboid-shaped ridge, and waveguide step, are employed to ease manufacturing difficulties at sub-THz frequencies. Thereinto, the trapezoidal irises replace the traditional multiple steps or long chamfers to simplify the waveguide transformer and shorten the path, the waveguide step widens the available bandwidth, and the cuboid-shaped ridge reduces the difference-port reflection and acts as a coupling probe for the sum-port to improve isolation. Moreover, a bed of nails is applied to the waveguide splitting-plane for electromagnetic (EM) leakage suppression and assembly convenience. To verify this WMT, a WR-4 band (170-260 GHz) prototype is fabricated and measured, showing an average combination efficiency of 92.2% within 175-255 GHz (37.2%-bandwidth). Then, the WMT is applied to a two-way combined solid-state power amplifier (SSPA) module. Thereinto, a contactless E-plane waveguide transition with unprecedented L-shaped chock grooves (LSCGs) is presented for waveguide system interconnection. In power measurement, the power combined module produces a maximum power output of 76.6-mW @ 216-GHz.