Waveguide Transmission Cavity with Losses

Abstract

Abstract : The symmetrical-but lossy-waveguide transmission cavity is analyzed with respect to resonant length, minimum and maximum insertion losses, and 3-db frequencies (loaded Q-factor). Losses are considered to originate both in the cavity proper and in the input and output discontinuities. A preferred representation of those discontinuities makes it possible effectively to lump all the various losses together. All the quantities of interest (resonant length, insertion losses and Q sub L-factor) are expressed in terms of the input and output discontinuity equivalent circuit. The results are quite general, but they will be of particular interest in the case of a transmission filter whose input and output are voltage controlled varactors. Normalized plots of resonant lengths, insertion loss at resonance, and Q sub L-factors conclude the study. The reactive component of the inputoutput equivalent circuit is the independent variable. The resistive component is the parameter. Loci of constant insertion losses, plotted on the Q sub L graphs, makes it possible to determine the maximum achievable Q sub L for a given insertion loss and resistive component; or the maximum resistive component for a given Q sub L and a prescribed insertion loss; or the minimum insertion loss for given Q sub L and resistive component.