Design of a Broad Bandwidth TM01 Mode Waveguide Bend for High-Power Microwave Applications

The TM01 mode bend is a key component in the high-power microwave (HPM) transmission system. Based on the coupling wave theory and the deformation of the elliptical cross section, a novel broad bandwidth 90? TM01 bend with an elliptical structure is proposed in this article. It is found that the interference modes can be effectively suppressed by controlling the variable curvature and cross section deformation of the elliptical waveguide, and the bandwidth of the bend can be significantly improved. Numerical calculation and simulation results illustrate that the maximum transmission efficiency at the central frequency (9.7 GHz) is 99%, and its bandwidth reaches 4.37 GHz when the conversion efficiency exceeds 95%, which increases near 126.8% compared with the conventional circular design. The S-parameter experiment and high-power test are conducted by connecting them with a vector network analyzer (VNA) and an HPM source, respectively. Measurement results indicate that the S21 of the bend is about -0.5 dB in the frequency range of 8-11.25 GHz, and it works stably when the microwave power is 4 GW. The experimental results indicate that this TM01 bend can be competently applied in the HPM system.