Microwave Leakage and Isolation in a Compact Coaxial RTTO Enabling Simultaneous Dual-Frequency High-Power Generation

This article addresses the critical challenge of microwave leakage that occurs in dual-frequency relativistic transit-time oscillators (RTTOs) during simultaneous high-power microwave (HPM) generation-a phenomenon primarily attributed to the non-cutoff characteristics of coaxial TEM modes. Through comprehensive theoretical analysis and particle-in-cell (PIC) simulations, we propose an approach for suppressing microwave leakage by optimizing the key parameters of the reflector cavity, which dramatically improves isolation indexes to 25.0 dB for X-band and 37.4 dB for Ka-band, respectively. Experimental validation in an anechoic chamber demonstrated that the optimized RTTO operates stably at 470.0 kV, 16.5 kA, and under a 0.6 T guiding magnetic field, simultaneously generating X-band (8.42 GHz) and Ka-band (30.62 GHz) microwave power of 1.44 and 0.38 GW with pulse durations of 50.0 and 28.0 ns, respectively. Spectral analysis verified the elimination of mixing components, thereby demonstrating proof-of-principle use of the RTTO as a multifrequency HPM source for future applications.