A High-Power Ka-Band Radial Transit Time Oscillator With Over-Sized Extractor

Abstract

Radial transit time oscillator (TTO) is a promising device to achieve a high-power Ka-band output. However, because the cavity number is limited, the power capacity of extractor and the radiation power are hard to improve. To solve this problem, a high-power Ka-band radial TTO with an over-sized extractor is proposed in this article. Taking the quasi-TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">02</sub> mode as working mode, the electric field distribution, beam-loading conductance ratio, and external quality factor prove that the electric field in the extractor can interact with the radial intensity electron beam efficiently. Particle-in-cell (PIC) simulation results prove that a constant magnetic field or decreasing magnetic field can confine electron movement effectively. Setting the imposed diode voltage to be 400 kV, the corresponding current is 7.5 kA, and the microwaves with the power of 1.13 GW, the frequency of 32.15 GHz, and the efficiency of 38% can be generated. When the output power saturates, the maximum radial electric field on the surface of the extractor is only 980 kV/cm, which verified the high-power capacity of the over-sized extractor. Taking ohmic loss into consideration, the proposed radial TTO made of low-loss material (e.g., copper) is potential to output giga-watt level high-power microwaves (HPMs) at Ka-band.