Design study of a 372 GHz higher order mode input coupler

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

TE10 R-TE11c input coupler for a low-THz gyro-TWA

The design of a fundamental rectangular-to-circular coaxial cavity input coupler for a low-THz gyro-traveling wave amplifier (TWA) is presented. Theoretical and numerical approaches to the design of the coaxial cavity input coupler are introduced. The design is optimized for operation between 360-384 GHz, achieving a transmission bandwidth of 7.5% (358-386 GHz). A comment on the manufacturability of sub-mm waveguide channels is included

Design study of a fundamental mode input coupler for a 372-GHz gyro-TWA I : rectangular-to-circular coupling methods

The design of two fundamental mode rectangular-to-circular waveguide input couplers for a low-terahertz gyrotron-traveling wave amplifier (gyro-TWA) is presented. A T-junction input coupler with a Bragg reflector and a multiple-hole directional coupler were optimized for operation between 360 and 384 GHz, the proposed gyro-TWA bandwidth. The T-junction coupler and the multiple-hole coupler achieved the respective bandwidths of 10% and 35%. The benefits and potential limitations of the low-terahertz wave coupler topologies are discussed alongside the challenging manufacturing methods of the submillimeter-wave components

A multiple-hole input coupler for a 372 GHz gyro-travelling wave amplifier

The design of a multiple-hole coupler that operates at a center frequency of 372 GHz for use in a gyrotron travelingwave amplifier (gyro-TWA) is presented. In simulations, the coupler achieved 35% bandwidth from 289GHz to–410 GHz with transmission losses of -0.5 dB predicted

Input coupling systems for millimetre-wave gyrotron travelling wave amplifiers

Input couplers for millimetre-wave gyrotron travelling wave amplifiers are presented in this study. A W-band input coupling system composed of a pillbox window, a smoothly curved waveguide bend, a T-junction and a broadband reflector was numerically optimised, constructed and measured. An average transmission coefficient of −2.0 dB over a designed operating frequency range was measured. Additionally, a higher-frequency input coupler for operation at a central frequency of 372 GHz was also designed based on a multiple-hole coupling configuration. The simulated transmission coefficient was −0.5 dB if the ohmic loss is not considered

Measurement of an upgraded input coupling system for W-band gyro-TWA

A gyrotron traveling-wave amplifier (gyro-TWA) operating at W-band has been upgraded and experimentally measured. In this paper, the design and measurement of the upgraded input coupling system for the gyro-TWA is presented. In the measurement, the transmission coefficient of the coupler is at an optimal level of about -1 dB

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 Braggtype 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

Input coupling systems for mm-wave amplifiers

Input couplers for mm-wave gyrotron traveling wave amplifiers (gyro-TWAs) were designed. A W-band input coupler composed of a T-junction and a broadband reflector was constructed and measured in W-band. It achieved a transmission coefficient of -2.2 dB including the pillbox window and a waveguide bend. A multiple-hole coupler was designed and simulated at 372 GHz. Without considering the Ohmic loss, in simulations the 372GHz coupler achieved a transmission coefficient of -0.5 dB

Design of a TE10-to-TE61 mode coupler for a 372 GHz gyrotron travelling wave amplifier

This paper presents the design of a TE10-to-TE61 mode coupler for a 372 GHz gyrotron travelling wave amplifier. The optimized coupler was able to achieve an -1 dB transmission over the frequency band of 360-384 GHz. The transmission decreases by 1.2 dB when the copper conductivity of 0.5E7 S/m was used in the simulation. The designed coupler was scaled to W-band for manufacture and measurement. The measured transmission and phase response confirmed the mode coupling between the input TE10 mode and the desired TE61 mode

Optical study of the electronic phase transition of strongly correlated YbInCu_4

Infrared, visible and near-UV reflectivity measurements are used to obtain conductivity as a function of temperature and frequency in YbInCu_4, which exhibits an isostructural phase-transition into a mixed-valent phase below T_v=42 K. In addition to a gradual loss of spectral weight with decreasing temperature extending up to 1.5 eV, a sharp resonance appears at 0.25 eV in the mixed-valent phase. This feature can be described in terms of excitations into the Kondo (Abrikosov-Suhl) resonance, and, like the sudden reduction of resistivity, provides a direct reflection of the onset of coherence in this strongly correlated electron system.Comment: 4 pages, 3 figures (to appear in Phys. Rev. B