Several novel compact circularly-polarized probe-fed annular-ring microstrip patch antennas are examined experimentally and numerically. In order to reduce the antenna size and provide a suitable input impedance match, two techniques are employed; the insertion of strips into the annular ring and placing a cross-slot into the ground plane. The proposed annular-ring patch with a cross-slotted ground plane yields a much smaller size for a given frequency. This novel patch antenna can effectively be reduced by about 55 percent in size compared to conventional annular-ring patch antennas. The antenna displays wide bandwidth and good circular polarization characteristics. The results of a parametric study for three novel strip-loaded annular-ring patch antennas and for the compact circular patch antenna augmented by a narrow annular ring with a cross-slotted ground plane are discussed in this paper.
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