Input impedance of probe-excited rectangular microstrip patch radiator

An expression for the input impedance seen by the coaxial line feeding a rectangular patch radiator is derived, taking the effect of wall admittance, conductor and dielectric losses into account. The real part of wall admittance of the patch radiator is determined from the angular spectrum of plane waves in the visible region of the wave-number plane, and its imaginary part is determined from the electric and magnetic energy stored in the region of the fringe field close to the radiating edges of the patch radiator. The electric field inside the patch radiator required for the analysis is expressed as a superposition of its resonant modes, the coefficients of which are determined in terms of wall admittance, surface impedance of the conducting boundary and amplitude of the exciting current. A comparison of the computed results with the available experimental data and theoretical results obtained by others is presented.