A Comparison of Some Methods for Corrugated Waveguides

Abstract

Singly and doubly periodic parallel plate waveguides can be investigated by means of a number of methods. The techniques considered here are: the null-field method, the modal theory approach and the method of multiple scales. This is a brief outline of a forthcoming article [1] and will only address one aspect of the subject. Previous null-field results [2,3] are compared with the corresponding results obtained by means of the modal [4] and multiple scales [5] techniques. The first two methods are found to be essentially equivalent whereas the last one gives more of a qualitative indication as to the effects of a periodic corrugation. The most important of these effects is the resonance phenomenon that gives rise to stopbands. The first thing to compare is therefore the ability to accurately determine, for example, the stopband width. As seen in Fig. 1 the multiple scales technique does not agree with the other two methods. This discrepancy is not accounted for when the corrugation is weak since the accuracy of a perturbation technique should improve with decreasing corrugation.