Spectral-domain analysis of multilayer cylindrical–rectangular microstrip antennas

In this paper, the resonance and radiation characteristics of multilayered cylindrical–rectangular microstrip antennas are analysed. The problem is formulated, in the spectral-domain, using an electric field integral equation and the spectral-domain Greenʹs function. An efficient compact method is developed to obtain the Greenʹs function of the electric field due to the current distribution of a patch located in an arbitrary layer of a cylindrical stratified medium. To accomplish this, efficient matrix representations are used to describe the electric and magnetic fields in each layer of the geometry in terms of ABCD matrices characteristic of its material properties. The boundary integral equation for the unknown patch current is solved numerically by applying the boundary element method using three kinds of basis functions. Taking into account the symmetry properties of the elements of the moment method matrix, the CPU time is reduced significantly. The convergence of the method is proven by performing the resonant frequencies for a single layer cylindrical–rectangular microstrip patch vs. the substrate thickness. The computed data are found to be in very good agreement with those found in the literature, using only two basis functions. Once the validity of the method is checked, further results for various antennas structures are presented proving the generality of the method. Finally, the effect of an air gap between the substrate layer and the ground conducting cylinder on far zone radiation field is investigated using the steepest-descent method.