Ultra-wideband printed ridge gap waveguide hybrid directional coupler for millimetre wave applications

The evolution of a wireless communication system to the fifth generation is accompanied by a huge improvement in the performance of the communication system through providing high data rate with a better coverage area. Hence, 5G technology requires access to millimetre wavebands where more spectra are available for high-speed applications. This technological progress motivates the research community to develop the essential microwave components, specially couplers, through the use of state of the art guiding structure such as printed ridge gap waveguide (PRGW). In this study, the design of ultra-wideband 3-dB planar quadrature hybrid coupler based on PRGW technology is proposed. A systematic design procedure for the proposed coupler is presented and illustrated. The proposed directional coupler is fabricated and measured, where the measured results show good agreement. The presented coupler covers over 26% bandwidth centred at 30 GHz. The presented coupler has a measured wide impedance bandwidth of a 26.5% centred at 30 GHz based on -10 dB threshold. The phase difference between output ports is 90 degrees +/- degrees 5 over 23% relative bandwidth. On the other hand, the total bandwidth is limited by the amplitude imbalance, which has a bandwidth of 13% for +/- 0.75 dB variation.