Spectral Domain Analysis of Microstrip Patch Antenna Currents and Radiation.

The conventional leaky cavity and transmission line models currently used to analyze microstrip patch antennas, although physically appealing and simple, do suffer from some drawbacks. These techniques require the radiating aperture admittance, a quantity not exactly known, and they do not explain the radiation mechanisms of the antenna well, nor do they predict the current on the top surface of the patch. This thesis reappraises the current models and techniques of microstrip antenna analysis in view of these deficiencies, and develops an alternative approach to determine the radiation. The integral equations governing the currents on an arbitrarily shaped patch antenna are formulated using a dyadic Green's function approach and then transformed into the spectral domain. These spectral domain equations are in a form suitable for numerical solution with the conjugate gradient-FFT technique. Computer code to implement this has been written for a two dimensional idealization of the general three dimensional problem. This simplified model of a patch antenna consists of a perfectly conducting infinite strip above a dielectric substrate backed by a conducting ground plane and excited from within by a transverse electric current sheet. Once the total current is found on this antenna, the top and bottom surface currents, far zone fields, radiating aperture admittance, and strength of the TM surface mode are also computed numerically. Exact simple relations for the far zone fields based on the total current of an arbitrary patch antenna are presented, without introducing the artificial radiating slots traditionally used. Based on results from the two dimensional model, the far zone fields can be reasonably predicted from the bottom surface current alone for the thin patch antenna. However as the thickness of the substrate or its dielectric constant increases, so does the importance of the top surface current. In addition, the antenna b and width and surface mode effects are shown to increase. Numerically computed values for the aperture admittance for various dielectric constants and thicknesses of substrate are also presented and compared with currently available approximate formulas.PhDElectrical engineeringUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/161746/1/8801447.pd