Input impedance of annular-ring microstrip antennas with a dielectric cover

A theoretical and numerical analysis of the annular-ring microstrip antenna with a dielectric cover is performed. The problem is formulated in the Hankel transform domain, taking a coaxial feed into consideration. The integral equations for the surface current density on the patch are derived. Galerkin´s method is used to solve for the surface current density, and a stationary formula for the input impedance is obtained. Numerical 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