A Novel \text} Mode Content and Relative Phase Analysis Technique

Overmoded relativistic backward wave oscillators (RBWOs) are usually difficult to achieve pure mode ouhowever, until now, radiation equipments for high power microwave (hPM) devices are only matched to a single operating mode. So it is unsuitable to utilize the ready-made hPM antenna to radiate mixed TM 0n modes with high radiation efficiency, and thus practical applications of the overmoded RBWO device becomes limited. For converting these hybrid TM 0n modes into a pure one (e.g., TM 01 or TEM mode), diagnostics of the overmoded RBWO's output mode is required. In this letter, a practical measurement technique without requiring high precision calibrations of the power distribution and relative phases between the TM 0n modes propagating in overmoded waveguide is described. This method is validated by measuring the output modes of a specially designed TM 01 -TM 0n mixed modes exciter.