Backward-Wave Oscillator with Distributed Power Extraction Based on Exceptional Point of Degeneracy and Gain and Radiation-Loss Balance

Abstract

We propose a new design paradigm for power efficient backward-wave oscillators (BWOs). Conventional BWOs exhibit small starting current and limited power efficiency. We introduce the concept of distributed radiation loss in a hot slow wave structure (SWS) working at an exceptional point of degeneracy (EPD) to achieve high power extraction from the electron beam aiming at high power efficiency. We show how the simultaneous presence of distributed radiation loss and distributed gain arising from the electron beam can be exploited to realize an EPD. In principle this new condition guarantees full synchronization between the electromagnetic (EM) guide mode and the charge wave for any amount of beam current and power extracted. We show how radiating EM modes (via distributed apertures) with backward propagation in the SWS and interacting with the charge wave are engineered to exhibit a second order EPD. We also show that including distributed radiation-losses in the design results in having high threshold current which implies higher power generation.