A compact 30 GHz low loss balanced hybrid coupler fabricated using micromachined integrated coax

Recent years have seen increased interest in the K and Ka frequency bands due to continued growth of satellite communications, particularly the USA Air Force Wideband Gapfiller Satellite (WGS) programme. This work presents a 4-port 30-GHz quadrature hybrid coupler fabricated using micromachined integrated coaxial line. The best electrical performance was measured at 31.6 GHz, where the amplitude and phase difference between the through and coupled ports are within 0.23 dB and 1.5°, respectively, of the nominal -3 dB, 90° design specification. The excess losses for the through and coupled port at 31.6 GHz are 0.31 dB and 0.54 dB. The overall footprint of the component is λ/10 by λ/5 at 30 GHz (1.0 × 1.7 mm), making this hybrid extremely small compared to alternative waveguide or coaxial designs. We believe this is the smallest coaxial hybrid coupler ever fabricated for 30-GHz.