Our analysis of the radiation of a rectangular patch antenna will be based on the cavity model from Chapter 3. Using two equivalent radiating apertures, we will derive expressions for the radiated field and directivity. A parametric study of the influence of various characteristics (substrate height and permittivity, antenna width, and truncation of the ground plane) will also take place.
The equivalent sources of the problem are the virtual magnetic currents which result from Huygens’ principle, with the associated concept of a radiating aperture. This approach is similar to that of the horn antennas, where knowing the electric field (or equivalent magnetic current) distribution in the aperture enables the radiation to be determined more easily than as a result of the distribution of the electric current on the metallic sides.
Note that the real sources are the electric currents and charges present in the metallic parts of the antenna. They constitute the unknown factors to be determined for a number of commercial software applications used in planar antenna design (such as IE3D or Ansoft Designer). This explains why nowadays engineers gain their understanding of the workings of an antenna from electrical current cartographies rather than 3D electrical field distributions, i.e. from magnetic currents.
However, the physical approach to radiation through the radiating aperture concept is often more pertinent than ...