Search

A high-power 200-GHz extended interaction oscillator (EIO) is designed by large-signal analysis. Analyzing different resonant modes, we calculated the mode called, here, as ${L}_{{1}} $ to be the most efficient one for our structure. From eigenmode analysis, it was predicted that the resonator-slow wave structure (SWS) coupling region has a considerable effect on resonant RF mode due to a ${L}_{{1}} \rightarrow {L}_{-{1}} $ mode transformation, where ${L}_{-{1}} $ is a parasitic low-output power resonant mode of the resonator. Using the eigenmode outcomes in addition to large-signal results, we found the optimum dimensions for the coupling region. The designed oscillator was then simulated by Particle-in-Cell (PIC) solver, leading to approximately the same results as those predicted by the mentioned procedure. The observed mode competition of different modes of the oscillator is analyzed and then removed by inserting a lossy layer at a proper location. By properly introducing a stub mode tuner near the output coupler, we could selectively excite the ${L}_{{1}} $ mode and maximize the RF output power to values even higher than those observed in the absence of mode tuner. Stable RF powers up to 2 kW are predicted to be obtainable by the sheet electron beams with beam densities lower than the state of the art.

The thermal simulation using ANSYS was carried out for estimating the maximum temperature and the temperature distribution in a high-average power broadband helix traveling-wave tube (TWT). The simulation was first carried out independently for the subassemblies such as the slow-wave structure, the output coupler, and the depressed collector; and the combined effect on the overall temperature inside the TWT was estimated subsequently. The simulation was carried out using several options of thermal interface resistances such as 100% contact and 50% contact, apart from considering various structural configurations, and an optimal thermal management solution was evolved for the device under consideration.

We present the design of a backward-wave oscillator based on a novel slow-wave structure (SWS) operating under low magnetic field conditions (

This work was supported by the Engineering and Physical Sciences Research Council (EPSRC) U.K. under Research Grant EP/K029746/1, and Science and Technology Facilities Council (STFC) U.K. under Research Grants ST/K006673/1 & ST/K006703/1, ST/N002326/1 & ST/N002318/1. An output coupler for a W-band high power wideband gyro-amplifier has been designed, manufactured and experimentally measured. It consists of a high performance sin2-parallel corrugated horn integrated with a broadband multi-layer window. The major design requirements are that the horn/window combination must have an input return loss lower than -30 dB over a 10 GHz bandwidth, provide a high quality output beam pattern, and operate under ultra-high vacuum conditions. The coupler converts a circular wave guide TE11 mode into the free space Laguerre Gaussian LG00 mode over the frequency band of 90–100 GHz with a measured return loss of between -30 and -40 dB and a simulated Gaussian coupling efficiency of over 99% at 94 GHz. Postprint

In this paper, we present an S-band compact metamaterial microwave source, which is based on a rectangular output coupler and a new all-metal metamaterial slow-wave structure that has been proposed previously. Due to the reversed Cherenkov radiation of the metamaterial, this metamaterial microwave source can be considered as a new sort of backward wave oscillators (BWOs). The S-band metamaterial microwave source has been further studied and analyzed by using Ansoft HFSS and CST Particle studio particle-in-cell solver. The simulated results show that the electronic efficiency of this S-band metamaterial microwave source can go up to 90% with the peak output power of 4.5 MW. When compared with conventional BWOs, it has obvious advantages such as miniaturization and high electronic efficiency.

A new type of input/output coupler for sheet beam traveling wave tube is designed, analyzed, and measured in this paper. In the design, a special sloped coupling aperture distributed between two paralleled rectangular waveguides in ${H}$ -plane is employed for compact dimensions, ease of fabrication, attainment of high power capacity, and more convenience for periodic cusped magnet focusing system. A nonlinear-curve profile with Chebyshev-curve distribution is applied to extend the operating frequency bandwidth while suppressing reflections to avoid generating oscillation in the slow-wave structure. Based on the analytical investigation and numerical simulation, an optimized sloping angle of the coupling aperture is obtained to improved performance. Simulations imply that the coupler achieves a broadband bandwidth ( $S_{11} dB) of 23 and 10 GHz in $W$ - and $Q$ -band, respectively, with coupling coefficient above −0.2 dB. Cold test results satisfactorily agree with simulations.

The design of a higher order mode (HOM) input coupler for a low-THz gyrotron travelling wave amplifier (gyro-TWA) is presented. A two-branch waveguide coupler based on the even distribution of incident power is designed to couple the rectangular TE10 mode to the circular TE61 mode. The optimised tapered waveguide input coupler achieved an operating frequency range of 359 – 385 GHz, equating to a bandwidth of 7%. A prototype waveguide coupler scaled to W-band (75GHz to 110GHz) was manufactured. Vector Network Analyser (VNA) measured return loss of the HOM coupler is shown to be < 10dB at 90 – 96 GHz. A transmission and phase measurement is presented to analyse TE61 mode conversion in the coupler.

In this paper, a quasi-optical (QO) output coupler, consisting of a tapered waveguide coupling to WR-10 waveguide, was designed to serve as the multigap output cavity of a 50-kW peak-power W-band sheet-beam klystron. In this structure, TE10 mode radiation from the gap ports is superimposed in the tapered waveguide coupling out to the external waveguide. In our numerical design, the circuit dimensions were systematically optimized by parametric finite-difference time-domain simulations; the 2 pi mode of the optimized QO output cavities (three, five, and seven gaps) have an external Q(Qe) of 650, an ohmic Q(Q 0) of 1650, and a total Q(Qt) of 460 at 95.4 GHz. The measured transmission coefficient (S 21) through the two QO external waveguide ports is in reasonable agreement with the transmission predicted from simulation. MAGIC3-D particle-in-cell simulation predicts that the QO output cavity stably produces more than 50-kW output power from a 70-kV and 3.6-A electron beam in the eight-cavity klystron circuit.

The description and theory of a method of generating harmonics of a microwave signal by deflection of an electron beam are presented, Examples of deriving output power at harmonics of the deflection frequency for either circular or linear deflection patterns and for both waveguide and cavity output are treated. The system is unusual in that there is power transfer between two streams of energy that are essentially orthogonal to each other in space. Moreover, since coupling of a wave is to the virtual motion of a space charge, which can move at any speed, there is no limitation on the phase velocity of the wave in the output coupler. While emphasis in this paper is on the output coupler, the practical problem of beam deflection is also treated. Finally, the principle of operation is demonstrated. Experiments with prototype models have produced up to 2 watts of 34-Gc power from an 8.5-Gc input, or a conversion efficiency of -24 db to this fourth harmonic.