Resonant frequency of a tunable rectangular microstrip patch antenna

The resonant frequency of a coaxial‐probe‐fed rectangular microstrip antenna tuned by a number of passive metallic posts suitably placed within the antenna's boundary is obtained by using the resonant frequency expression in the absence of the post. The resonant frequency in the absence of the post is calculated from the fringing field extension and effective relative permittivity expressions. The theoretical resonant frequency results of tunable rectangular patch antenna obtained by using this method are in good agreement with experimental results available in the literature.