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The conventional circular waveguide 90° TE01 bend makes it difficult to achieve broadband because of the serious interference from TM11 mode. To solve this problem, the mode coupling characteristics in the hexagonal waveguides are investigated in this paper, and it is found that when the deformation amplitude is appropriate, not only the degradation between TE01 and TM11 is broken but other parasitic modes can be efficiently suppressed. Based on the analysis, an oversized broadband TE01 waveguide bend with variable curvature is proposed, and its transmission efficiency is over 95% from 8.5 to 11 GHz, while its structure length is only 26.16 times wavelength. Measurement results indicate that the S21 of the bend is about −0.4 dB from 8.5 to 11 GHz, and it works stably under a microwave output power of 1 MW. The consistency between theoretical calculations, simulation, and experiments indicates the feasibility of this novel TE01 bend. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Mode converter is one of the most important devices in the high-power microwave (HPM) applications. To conduct an in-depth research for the orthogonal mode converter, a novel 90° compact TM01-TE11 circular waveguide converter working at 9.7 GHz is proposed in this article. This design innovatively integrates the traditional mode converter with 90° bend techniques based on the mode coupling theory, which ensures a compact structure and high-power handling capacity. Calculated and simulated results illustrate that the maximum conversion efficiency of the converter at central frequency reaches 99.4% when the structure length is 535 mm, and the bandwidth reaches 680 MHz when the conversion efficiency exceeds 95%. For demonstration, a prototype is fabricated, and the corresponding experiments are investigated. According to the $S$ -parameter measurement, it has a high conversion efficiency at central frequency. Meanwhile, the high-power performance is conducted by connecting it with a relativistic backward oscillator (RBWO), and the converter works stably under a maximum output power of 4 GW. The good agreement of the theoretical analyses, simulations, and experimental results indicates the feasibility of the proposed converter. [ABSTRACT FROM AUTHOR]