The design of a monopolar square-ring patch antenna with wideband operation is presented. The antenna consists of a parasitic square-ring patch antenna that is shorted to the ground plane through two shorting walls and is excited by a top-loaded coaxial probe. The key design parameters to obtain 50 /spl Omega/ input impedance and optimum bandwidth are investigated experimentally. The effects of the inner slot size of the square-ring patch on the operating frequency of the proposed antenna are also studied. From the obtained results, a 10 dB-input-impedance bandwidth of more than 50% can be achieved while the side length of the square-ring patch is about 0.3 free-space wavelengths and the antenna height is less than 0.1 free-space wavelengths. Also, the antenna can provide stable monopole-like conical radiation patterns across the impedance bandwidth.