Analytical Study of Annular-Ring Microstrip Antennas Shorted With Thin Wires

A new theoretical analysis method is presented for annular-ring microstrip antennas with a short-circuited wall implemented as an array of thin cylindrical wires. Assuming wire spacing to be small compared to wavelength, the averaged boundary conditions are employed. An explicit characteristic equation, which determines resonant frequencies depending on wire spacing and radius is derived. A calculation technique for antenna input impedance is presented. Obtained results show good agreement between theoretical and experimental data. It is shown that the wire short-circuited wall can bring considerably different resonant properties compared to continuous metallic one.