Development of a 85∲115 GHz 90-deg phase shifter using corrugated square waveguide

A 90-deg differential phase shifter using corrugated square waveguide structure has been developed for 86 GHz band VLBI dual-circular polarization observation. The 90-deg phase shifter was designed to have two corrugated walls inside the square waveguide so that the vertically and horizontally polarized waves at the output port have phase differences of 90 ± 3.3 degrees across 85~115 GHz band. Measurements show that the return and insertion losses for both polarizations are better than 17 dB and ~0.2 dB, respectively. The axial ratio is estimated to be less than 0.6 dB within the required frequency band.