Design of an Omnidirectional Circularly Polarized Antenna

In this letter, an omnidirectional circularly polarized (CP) antenna is proposed. This new antenna has a simple structure, which is composed of two dielectric substrates, four shorting pins, and a feeding pin. A CP radiation can be realized at the azimuth plane. This antenna can cover broad communication bands, such as GSM900, GSM1990, PCS, and UMTS bands. To validate the correctness of the simulation results, the omnidirectional CP antenna was fabricated and measured. With a profile of 0.066 lambda(0) (lambda(0) is the free-space wavelength at the lowest frequency during the operating bandwidth), the antenna has a -10-dB impedance bandwidth of 25.6% (range from 1.7 to 2.2 GHz) and a 3-dB axialratio bandwidth of 34.7% (range from 1.57 to 2.23 GHz). At the center frequency 1.95 GHz, the measured average axial ratio and right-hand circularly polarized gain are 2.69 dB and -1.12 dBic at the azimuthal plane, respectively.