RADIATION MODES OF OPEN MICROSTRIP WITH APPLICATIONS

The well known bound modes of open microstrip do not constitute a comp lete spectrum, for, continuous radiation and localized (reactive) mode s are excited at discontinuities in microstrip circuits and antennas. This part of the spectrum has not been investigated before so that, up to date, radiation problems in microstrip are being investigated by n onmodal methods, such as the moment method. We derive here for the fir st time the complete spectrum of open microstrip, including one or mor e bound modes and a continuum, and demonstrate its straightforward app lication to a practical problem such as the excitation by a cylindrica l probe of finite radius. Application of Lorentz's reciprocity princip le is now possible in complete analogy to the problem of excitation of a close waveguide by a probe. Mode patterns, the equivalent circuit o f a via-hole and its radiation pattern are characterized as a practica l application of the foregoing theory.