在Ku波段低磁场相对论返波管中, 由于阴极发射的角向不均匀性, 产生的微波除了TM01模, 还有主模TE11等其他微波模式。由于目前设计的圆波导耦合器只能测量TM01模式功率, 其他微波模式存在会导致在线微波波形异常, 给在线测量带来困难。本文设计了一种模式抑制器, 其结构由5个腔组成。通过数值模拟和实测结果得出: TM01模在频率14.8~15 GHz衰减小于0.1 dB, 而对其他模式, 如主模TE11模式微波能够全反射。模式抑制器置于相对论返波振荡器(RBWO)与圆波导耦合器之间, 实验观察在线输出微波与辐射场波形一致, 微波功率符合较好。

There are many other modes besides TM01 mode in Ku-band relativistic backward wave oscillator working at low magnetic field due to inhomogeneous emission of explosive cathode. The circular couplers currently used are for pure TM01 mode only. The measurement will be disturbed by other modes and the waveform obtained will be abnormal, which will make measurement difficult and inaccurate. A mode suppressor consisting of five cavities is designed in this paper. The attenuation coefficient of the mode suppressor is lower than 0.1 dB for TM01 mode between 14.8 GHz and 15 GHz according to the simulation and measurement results. Other modes are total reflective for comparison. The mode suppressor is placed between Relativistic Backward Wave Oscillator(RBWO) and coupler in the experiment. The waveforms obtained from coupler as well as the output power are consistent well with that from radiation field, indicating beneficial effect of the proposed mode suppressor.