SPECTRAL-DOMAIN ANALYSIS OF HIGHER-ORDER LEAKY MODES IN MICROSTRIP LINES - A NEW SPECTRAL-GAP EFFECT

This paper analyzes leaky modes in open microstrip lines. The differen t possibilities and implications of the choice of the inversion contou r associated with the spectral domain analysis are investigated. Speci fically, we have focused on the leaky solutions obtained when the inve rsion contour entirely lies either on the proper sheet or on the so-ca lled outgoing sheet. Solutions computed on the proper sheet can be con sidered surface-wave leaky modes and those computed on the outgoing sh eet volume-wave leaky modes. The continuity between the different boun d and surface-wave/volume-wave leaky solutions has been studied. A new kind of spectral-gap effect has been found as a consequence of such s tudy.