Moment-method determination of the surface currents and fields radiated by rectangular microstrip patch-antennas

A quantitative solution is presented of the surface currents and the corresponding fields generated in free space by electrically thin microstrip patch-antennas of rectangular configuration. Use is made of a versatile analytical tool known as the method of moments, in which the surface current density is approximated by a series expansion involving piece wise linear basis functions and weighted superposition coefficients which are to be determined. It is shown that when the governing integro-diflerential equations are reformulated in matrix form involving generalized network parameters, the desired current distribution emerges in a simple compact form. A remarkable feature of the result of the present analysis is the fact that the field induced in the substrate is due to a finite charge distribution rather than the previously implied phenomenon, viz. the influence of an infinite charge distribution. Indeed, the charge distribution responsible is directly derivable from the time-harmonic continuity equation. All numerical results displayed are based on the use of plane-wave irradiation and the paper includes a discussion of certain practical feed arrangements as well as some practical applications. Results are presented in graphical forms within the frequency limits 1157-1237 MHz for two different sizes of the conducting patch.