Waveguide Coupler with Self-Contained 90° Polarization Rotation for Integrated THz Waveguide Circuits and Systems

In this paper, a waveguide coupler with 90° polarization rotation capability is presented for the first time. Different from conventional waveguide couplers, the proposed waveguide coupler has two E-plane and H-plane ports, which makes it very useful to connect E-plane and H-plane waveguide circuits and systems free from the use of additional waveguide twists, thereby reducing the complexity of integration and alleviating waveguide associated losses and mismatches. To validate this concept, a prototype was fabricated and measured. Measured results exhibit both return loss and isolation higher than 20 dB, with an amplitude unbalance of 0.5 dB over 140–160 GHz frequency range. In addition, the coupler length is only
$0.5\lambda$
, where λ is the wavelength at the center frequency. To the best of the author's knowledge, this is the most compact coupler ever demonstrated so far, making it an attractive candidate for compact integrated waveguide circuits and systems.