Validation of a 4-Port and 3-Port Rat-Race Balun for the 60 GHz- Band

This work presents a rat-race coupler as a balun for the 60 GHz-band. To simplify the structure, also the 3-port rat-race balun is also simulated and manufactured to compare these two balun types. They were analyzed with a vector network analyzer (VNA) and show in the frequency range of 58 GHz to 63 GHz a maximum insertion loss of 3.5 dB and 3.9 dB, respectively and a return loss of 10 dB or less. The common mode rejection ratio (CMRR) is better than 17 dB. The insertion loss and the return loss can further be improved within a measurement setup with connectors with less reflections. It was shown that a 3-port rat-race balun is a valid alternative and has advantage in size and complexity over marchand baluns or substrate integrated waveguide (SIW) baluns.