Quasistatic capacitance and frequency-dependent effective permittivity of multilayer microstrip patch antennas

A variational method in the spectral domain is used to determine the quasistatic capacitance of a patch antenna within a nonhomogeneous multilayer structure. The patch is modelled both by a one dimensional analysis using a segment of an infinite transmission line and by a full two-dimensional representation. A new technique is presented for determining the relative permittivity of an equivalent single-layer structure, from which the frequency-dependent effective permittivity is obtained. Results for a number of different antenna structures are given and show good agreement with measured values