A 230–300 GHz low-loss micromachined waveguide hybrid coupler

A silicon micromachined waveguide hybrid coupler for J-band (220–325 GHz) applications is presented. The coupling and phase shifting functions are realised using a 90° ridged waveguide phase shifter, a joint waveguide section and a port extension. The hybrid coupler is fabricated using a micromachined waveguide technology employing a double H-plane split that results in low losses. For the design band 230–300 GHz, initial VNA measurements indicate coupling coefficients of −3.2±0.4 dB, amplitude imbalance better than −0.5/+0.3 dB, phase imbalance better than −14°/+11° and an input reflection coefficient below −14 dB. To the best of our knowledge, this is the first time a low-loss micromachined hybrid coupler of this type is characterised within this frequency range.