Adiabatic Performance Evaluation System for Waveguide Transmission Lines

Abstract

In a temperature-controlled radio frequency (RF) power measurement system, there is a temperature difference between the system and the environment temperature. If a metal waveguide is used in the system, heat can reach the core of the system and affect the measurement. An adiabatic waveguide is utilized to reduce this heat flow. This article introduces several WR10 rectangular waveguides that are used in the Korea Research Institute of Standards and Science (KRISS) microcalorimeter and an evaluation system that can measure the adiabatic performance of the waveguides via a thermostat. The basic concept and measurement setup for the evaluation system are briefly introduced, and the structure and the function of the waveguide heat source and heat sense modules of the thermostat are presented. The test results of the adiabatic performance of several WR10 rectangular waveguides are compared and the electromagnetic performance is presented. We also tested preliminary dielectric waveguides that have been co-studied with Physikalisch-Technische Bundesanstalt (PTB), Germany recently. We propose an index to characterize the adiabatic performance of the waveguides. Based on the index results, we improve the adiabatic performance of our newly electroforming-processed adiabatic waveguide with a thick resin coating, which is forty times higher than that of the prototype KRISS microcalorimeter adiabatic waveguide. Finally, we fabricated and investigated dielectric waveguides that have a superb adiabatic property for the microcalorimeter application.