In this paper it is shown that a novel transition may occur for dominant leaky modes on microstrip line, between a leaky mode that leaks into the TM0 surface-wave and one that leaks both into the TM0 surface wave and into space. The evolution of these leaky modes is studied as a function of frequency by means of a full-wave spectral domain approach, and it is shown that such a transition may occur on microstrip lines that have a critical strip width, which is relatively large. The continuous-spectrum current excited by a finite source can be significantly enhanced when the frequency is near the transition frequency, resulting in very high spurious effects.
Baccarelli, P. (2005). Novel modal transitions for leaky modes on microstrip lines. In Proceedings of the 28th General Assembly of the International Union of Radio Science (pp.1-4). Ghent : International Union of Radio Science.