INPUT IMPEDANCE OF ANNULAR-RING MICROSTRIP ANTENNAS WITH A DIELECTRIC COVER

A theoretical and numerical analysis is performed on the annular-ring microstrip antenna with a dielectric cover. The problem is formulated in the Hankel transform domain, taking a coaxial feed into consideration. First the integral equations for the surface current density on the patch are derived. Galerkin's method is then used to solve for the surface current density and a stationary formula for the input impedance is obtained. Numeric-al results showing the effects of a dielectric cover on the TM12 mode of the annular-ring are given. It is found that the dielectric cover reduces the resonant frequency, decreases the resonant resistance and increases the impedance bandwidth.