A four-port quasi-optical circulator has been designed, built and tested for operation in the millimetre wave band. The specific circulator reported here was investigated over a 20 GHz bandwidth, centred on 94 GHz. Good performance characteristics were obtained over this bandwidth. Isolations of better than 30 dB and insertion losses of around 0.5 dB were achieved. The input vswr was found to be less than 1.35 over the whole bandwidth investigated and vswr’sof less than 1.1 were achieved for narrower bandwidths. It is possible of course to configure the 4-port circulator as a 3-port circulator, or indeed as 2-port isolator. Further optimization and consequent improvements in performance are almost certainly obtainable.
M. R. Webb, M. R. Webb,
"A mm-wave four-port quasi-optical circulator", Proc. SPIE 1514, 15th International Conference on Infrared and Millimeter Waves, 15146I (1 December 1990); doi: 10.1117/12.2301644; https://doi.org/10.1117/12.2301644