A microstrip monopolar patch antenna with shorting vias in the circular patch and coupled ring for bandwidth enhancement is proposed. The bandwidth of the proposed antenna with shorting vias in the annular coupled ring is over 40% wider than that of the antenna without shorting vias in the annular ring. The proposed antenna provides a wide bandwidth because of four resonant modes, including the TM01 mode of the circular patch, TM01 mode of the coupled annular ring, TM02 mode of the circular patch, TM02 mode of the coupled annular ring. These modes can generate a omnidirectional pattern in the azimuth plane like a monopole antenna. A prototype was fabricated to confirm the simulation verdictions. Measured results show that 10-dB return loss bandwidth of 38.4% from 4.42 to 6.52 and average gain of 5 dBi acrossing the operating band are achieved for the proposed antenna with a low profile of 0.027 wavelength.
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