Investigation into the Effect of Dielectric Loss on RF Characteristics of Helical SWS

Abstract

A general theory has been developed to account for the effect of the dielectric loss of discrete rods on the performance characteristics of an actual helical slow wave structure (SWS). The effect of the lossy dielectric rods has been studied on various propagation parameters, namely, phase propagation constant, interaction impedance and attenuation constant at different operating frequency. It is clearly shown that the influence of dielectric loss on RF characteristics is much larger at the millimeter frequency band than that at the microwave frequency band, especially on interaction impedance and attenuation constant. The general theory developed here has been further confirmed by comparing the results with those obtained elsewhere for some special cases.

Analysis of Dielectric Loss in a Helix Slow-wave Structure

“…2 vis-à-vis published theoretical results of Duan, et al [11]. The present simple method shows excellent agreement against that of a rigorous and computation intensive tape-helix model.…”

“…The method consists in finding the shunt capacitance (C) and shunt conductance (G) per unit length of the transmission line equivalent to the SWS, and then interpreting these parameters for the dielectric attenuation constant of the structure. The formula thus arrived at has been benchmarked against published results of Duan, et al [11] and excellent agreement was found. The analysis has been subsequently applied in predicting the dielectric loss in typical C-Ku band and Ka band helical SWSs, and variation of dielectric loss with temperature.…”

“…For benchmarking of the approach, we considered a practical helix SWS, for which the dimensions and dielectric attenuation values are published in the literature [11]. The proposed based on equivalent circuit analysis to find the dielectric attenuation constant (a d ) of the helical SWS, and a closed form expression for the dielectric attenuation constant has been derived that provides direct relationship with the structure-dimensions and material properties.…”

“…Estimation of conductivity losses in helical SWS has been widely treated in the literature [3,9] by theoretical approaches based on field analysis, and by measurement as well. However, the analysis of dielectric losses in helical SWS has received very little attention in the past, except an early work of Hagmann [10] and a recent one by Duan, et al [11]. Work of Hagmann [10] treated dielectric loss in a coaxially placed dielectric material at the centre of the helix relevant for the design of applicators for microwave hyperthermia.…”

“…Work of Hagmann [10] treated dielectric loss in a coaxially placed dielectric material at the centre of the helix relevant for the design of applicators for microwave hyperthermia. Analysis of Duan, et al [11] proposes a rigorous tape-helix model that gives dielectric attenuation constant as a solution of a transcendental dispersion relation containing complex variables, and one cannot use the dispersion characteristics obtainable from any other model to compute the dielectric loss using their approach. In this paper, a simple method is …”