Design of a Truncated Polarizer for a 263 GHz Gyro-TWT

For the operation of a helical-waveguide gyro-TWT a circularly polarized microwave, which is co-rotating with respect to the beam electrons, is required in the interaction region. Hence, the linearly polarized input wave has to be converted into a circularly polarized one. A polarizer based on a truncated circular cross-section at 263 GHz (G-band) is presented. The final polarizer is able to produce a circularly polarized wave at its output with an axial ratio of below 1.22 and a bandwidth of 20 % around its center frequency. Additionally, a reflection better than -30 dB and an insertion loss of below 0.3 dB are achieved. Furthermore, it is found that the bandwidth does not dependent on the taper length.