A broad-band annular-ring microstrip antenna

A heuristic discussion of the radiation properties of the transverse magnetic (TM11) and (TM12) modes of the annular-ring microstrip antenna is presented, indicating the possibility of the TM12mode as a superior microstrip antenna. Rigorous analyses of the resonant frequency characteristics of the antenna are then performed with the matched asymptotic expansions technique and the perturbation approach. The analyses show that the TM12mode is decidedly the best mode for microstrip antenna applications while the TM11mode, having a high -factor, is best reserved for resonator applications. The analyses include the study of the resonant frequencies, bandwidths, and radiation pattern of the antenna. The matched asymptotic expansions technique and the perturbation approach are also shown to agree excellently with each other within their domain of validity.