Radiation of a patch antenna on a finite substrate

The radiation pattern of patch antennas may considerably be affected by the finiteness of the substrate, especially when surface waves are strongly excited. In particular, the correct prediction of the diffraction contributions from the edges of the finite substrate is relevant when the patches are printed on free standing structures, in which the front-to-back ratio has to be maximized. A high-frequency solution is presented for the field radiated by a patch current distribution located upon a rectangular, grounded dielectric slab. The typical values of thickness and dielectric constant used in patch antennas suggest the effective use of a physical optics (PO) approximation, which consists of estimating the radiating equivalent currents distributed on the surface and in the volume of the entire finite slab, like those induced by the source in the infinite structure. The technique developed by Borselli, Maci and Rossi (see MMET '94, Kharkov, Ukraine, 1994) is applied to find the radiation of a patch on a finite substrate. By using a proper GTD ray tracing, the canonical solution is applied to the case of a dipole on a finite, rectangular grounded slab. Next, by integrating the contributions of each element of a current distribution, the radiation of a patch on a finite substrate is modeled.