Theoretical and experimental investigations on a compact TE11 mode bend for high-power transmission line

The oversized TE₁₁ mode bend is able to make the transmission direction of electromagnetic wave to turn 90°, and it is one of the key components in the high-power microwave system. The mode coupling characteristics between the TE₁₁ and parasitic modes under two different polarisations in the bending waveguide are analysed, and it is found that the TE₁₁ suffers less interferences from parasitic modes when its polarisation direction is perpendicular to the bending plane, and the corresponding 90° TE₁₁ bend is easier to realise high performance. To verify this analysis, an oversized 90° TE₁₁ bend waveguide working at 10 GHz is designed, and its structural length is only 7.5 times the central working wavelength. Simulated results indicate that its relative bandwidth is 15.6% when the transmission efficiency is over 98%, and its maximum power handling capacity reaches 5.6 GW at short microwave pulse duration (less than 100 ns). The S-parameters indicate that its S₂₁ is about −0.1 dB from 9.5 to 10.5 GHz, and its S₁₁ is under −25 dB in the same frequency range. Meanwhile, the high power test indicates that the bend works stably when the injected power is 3 GW.