Design of Wideband Waveguide Hybrid With Ultra-Low Amplitude Imbalance

We present a design and synthesis procedure for a new 90
^°
waveguide hybrid with ultra-low amplitude imbalance. This novel hybrid design is based on Reed's multiple branch waveguide hybrid. The primary feature of this quadrature hybrid design is the introduction of a controllable ripple in the operational band by, firstly changing the heights of the input and output branches and, secondly, by introducing three waveguide-height discontinuity sections placed symmetrically in the main waveguide. This layout allows ultra-low amplitude imbalance over a wide operational band. At the same time, it permits a greater input/output branch height as compared to the Reed's 5-branch waveguide hybrid, which should ease fabrication for short-mm and sub-mm wavelengths. This design concept is demonstrated through a 90
^°
waveguide hybrid for the 159-216 GHz band (30% fractional bandwidth). Our simulations indicate that the amplitude imbalance of the hybrid is better than 0.2 dB over the most of the 159-216 GHz band with a phase imbalance better than ±4
^°
. Experimental verification of the hybrid shows excellent agreement with the simulations.