A low loss rat race balun in gap waveguide technology

Hybrid ring (or rat-race coupler) has found many applications in millimeter and sub-millimeter wave technology. This paper describes a new type of hybrid ring realized in the ridge gap waveguide technology. The advantages of the new gap waveguide hybrid ring are low manufacture cost since the good electric contact between metal plates is not required, and lower transmission loss compared to microstrip line since there is no dielectric material needed. In addition, the gap waveguide technology opens up the possibility of waveguide integration circuit from millimetre wave up to terahertz. The focus of this work is on the realization of the new hybrid ring at 16 GHz, for the sake of concept verification. The simulated and measured results show that this structure works well and has a frequency band of 2.5 GHz around 16 GHz, with the reflection coefficient below -10dB and the phase difference between two output ports of 180° ± 5°.