Design and Experiment of a Compact Circular Waveguide TM₀₁ to TE₀₁ Mode Converter

In this article, a compact TM $^{\circ }_{{01}}$ to TE $^{\circ }_{{01}}$ (symbol $\bigcirc $ represents the circular waveguide) mode converter for X-band high-power microwave (HPM) applications is designed, fabricated, and experimentally verified. The proposed device comprises three parts, which are a TM $^{\circ }_{{01}}$ to vertical polarization (VP) TE $^{\scriptscriptstyle \square }_{{10}}$ (symbol □ represents the rectangle waveguide) mode power divider, a horizontal polarization (HP) TE $^{\scriptscriptstyle \square }_{{10}}$ to TE $^{\circ }_{{01}}$ mode power combiner, and an N-way TE $^{\scriptscriptstyle \square }_{{10}}$ circumferential array polarization torsion structure (CA-PTS). The first two parts utilize the topologic structures of radial power dividers (RPDs), which are then connected by the CA-PTS. This novel methodology makes the input and output ports of the mode converter on the same axis, with the transverse and longitudinal dimensions of approximately $8.6\lambda _{{0}}$ and $3.5\lambda _{{0}}$ , respectively. Simulation results of the TM $^{\circ }_{{01}}$ to TE $^{\circ }_{{01}}$ mode converter demonstrate that the return loss is better than −15.0 dB from 8.28 to 8.74 GHz, while the insertion loss remains below −0.2 dB, and a remarkable conversion efficiency achieves 99.21% at the center frequency of 8.4 GHz. An 18-way prototype was subjected to experiments. The measured S-parameter results of the setup were in good agreement with simulation one. Under an input power of 0.5 W, the simulated maximum internal electric field measured 943 V/m, and the power handling capacity (PHC) was also validated in the HPM test.