P. McElhinney

A high directivity broadband corrugated horn for W-band gyro-devices

A quasi-optical mode converter in the form of a corrugated horn has been designed through numerical simulations, manufactured and experimentally measured for application in W-band gyro-devices. This horn converts a cylindrical TE11 mode into a free space TEM00 mode in a frequency band of 84-104 GHz with a reflection better than 30 dB, a Gaussian coupling efficiency of 98% and directivity of 26.6 dB at 95 GHz. The small beam waist makes such a horn ideal for use with a depressed collector system. The measured results are in excellent agreement with the numerical simulations.

Design and Measurement of a Broadband Sidewall Coupler for a W-Band Gyro-TWA

The input coupler is an important component for a microwave amplifier. In this paper, a sidewall single-hole input coupler for a W-band gyrotron traveling-wave amplifier that operates at the frequency range of 90-100 GHz was designed and measured. Instead of using a cutoff waveguide, a broadband Bragg-type reflector with a small spread in phase was optimized for use as part of the input coupler. The minimum radius of the reflector was two times the size of a cutoff waveguide, which reduced the possibility for some of the beam electrons being collected in this section and lost to the amplifier interaction region.

Wide-band HE11 mode terahertz wave windows for gyro-amplifiers

Broadband HE11 mode output windows, based on the multilayer concept, are studied for high power gyro-amplifiers operating in the low terahertz region. As the wave power in the hybrid HE11 mode is concentrated in the center of the circular waveguide, smaller reflection and better coupling to the fundamental free space Gaussian mode can be achieved for the windows. Two windows are designed for optimized performance through simulations for operation in two frequency ranges of 360- 400 GHz and 90-100 GHz. The simulated performance, practical constraints in realization and manufacturing methods of the 90-100 GHz window is discussed. This window was constructed and microwave properties measured showing a lower than -27 dB reflection. This result agrees with simulation data which validates the simulation methodology and effectiveness of the design.

An Output Coupler for a W-Band High Power Wideband Gyroamplifier

An output coupler for a W-band high power wideband gyroamplifier has been designed, manufactured, and experimentally measured. It consists of a high performance sin2-parallel corrugated horn integrated with a broadband multilayer 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 ultrahigh-vacuum conditions. The coupler converts a circular waveguide 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.

W-band Gyro-BWO with a Four-stage Depressed Collector

An energy recovery system using a four-stage depressed collector was simulated and designed to improve the overall efficiency of the W-band gyrotron backward wave oscillator (gyro-BWO) at the University of Strathclyde. The spent beam information was exported from the simulation of the gyro-BWO using the 3D PIC code MAGIC. The geometry of the depressed collector was optimized using a genetic algorithm to achieve the optimum overall recovery efficiency for specific parameters of the spent beam. Secondary electron emissions and their effects on the recovery efficiency and the backstreaming of the electrons from the collector region were simulated. The heat power distribution on the electrodes was also simulated to avoid the “hot spot”.

Design and Measurement of a W-Band Brewster Window

A Brewster window integrated into a corrugated waveguide was designed, manufactured and studied for a W-band gyrotron traveling wave amplifier. A corrugated waveguide intended to guide a quasi-plane wave ( HE11) through the window, was numerically optimized and verified by measurement using a Vector Network Analyzer. The Brewster window was measured to have a reflection lower than -22 dB for the TE11 mode over the frequency range of 85-101 GHz.

Latest development of a W-band Gyro-TWA based on a helically corrugated interaction region

Latest development and experimental study of a W-band gyro-TWA with a helically corrugated waveguide and a cusp electron gun are presented. With an input seed signal from an 1.5 W, 90-96 GHz solid state source a gain of 27 dB was measured from the experiment. The bandwidth of the gyro-TWA was measured to be at least 5 GHz.

An input coupler for a W-band gyro-TWA

The input coupler that is used to launch the desired wave into the interaction region is an important component for a gyro-TWA. In this paper, a side-wall rectangular-to-circular coupler aiming to achieve a high coupling coefficient was designed for a W-band gyro-TWA. A broadband reflector was optimized to take the place of the cut-off waveguide to allow a much bigger beam tunnel to reduce the alignment difficulty.

W-band gyro-TWA using a cusp electron gun and a helically corrugated interaction region

Theoretical calculation, numerical simulation and experimental development of a W-band gyro-TWA with a helically corrugated waveguide and a cusp electron gun are presented. The cusp gun generated a 40 keV, 1.5 A axis-encircling electron beam. The maximum output of the gyro-TWA was predicted to be 5 kW with a 3 dB frequency bandwidth of 90-100 GHz and a saturated gain of 37 dB. The latest experimental results will be presented.

A broadband corrugated horn for a W-band gyro-TWA

A quasi-optical mode converter in the form of a corrugated horn has been designed and optimized through numerical simulations for a W-band gyrotron traveling wave amplifier (gyro-TWA). This horn converts a cylindrical TE11 mode into a free-space TEM00 mode in a frequency band of 90 GHz to 100 GHz with a return loss better than −35 dB and a Gaussian coupling efficiency of 97.8%.