HE04 Mode Exciters With Flat Transmission and High Mode Purity for Confocal Gyro-TWAs

A new topology to excite the HE₀₄ mode in wide bandwidth for confocal gyro-TWAs is presented. The mode exciter consists of a TE₀₄ mode exciter and a TE₀₄–HE₀₄ transition waveguide section formed by two cascaded one-stage tapers. In addition, the closed-to-open confocal waveguide boundaries are studied. Numerical results show that the port reflection of the whole structure is well below −10 dB over 90–110 GHz; the transmission of HE₀₄ mode is better than −1 dB over 94–107 GHz. Even more important, a maximum transmission variation of less than ±0.15 dB over the 1-dB bandwidth and a mode purity of better than 97.2% over the 3-dB bandwidth are achieved. The mode exciter is compact and easy to be fabricated, which can be applied to cold-test experiments of confocal gyro-amplifiers circuits.