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A compact single-feed circularly polarized microstrip antenna is proposed to achieve symmetric radiation pattern over a wide range of observation angles. In order to reduce the radiation aperture and consequently broaden the circular polarization (CP) and the half power beamwidth (HPBW) of the antenna, a partially etched superstrate and a conducting cavity are employed in the design. Further, reasonable axial ratio (AR) and impedance bandwidths are realized within the compact structure by using a simple series crossed-slot aperture coupled feeding. As a consequence, the overall dimension of the fabricated prototype is 0.32λ0× 0.32λ0× 0.12λ0at the center operating frequency of 1.56 GHz, and a 3.0% overlapped bandwidth of 10 dB return loss (RL) and 3 dB AR is obtained. Within the bandwidth, symmetric CP radiation pattern over almost the entire upper hemisphere is observed and the HPBW is also increased from 60° to 106°.

A circularly polarized (CP) Microstrip Yagi array antenna (MSYA) is designed in order to achieve high front-to-back ratioR(F/B)and high gain over wide range in the forward radiation space. A Wilkinson power divider owning two output ways with the same magnitude and different phase is used to feed the antenna. Parametric studies are carried out to investigate the effects of some key geometrical sizes on the antenna’s performance. A prototype of the antenna is fabricated, and good agreement between the measured results and the numerical simulations is observed. The overlap bandwidth of VSWR ≤ 1.5 and AR ≤ 3 dB is about 11%. The steering angle (α) between the peak gain direction and the broadside can achieve 35°,R(F/B)reaches 19 dB, and the gain at the front point (G0) is only 4.3 dB lower than the maximum gain (Gm). The antenna has a wide beamwidth CP radiation pattern over wide spatial range including 0° ≤θ≤ 90° in vertical plane and −35° ≤φ≤ 55° in horizontal plane.

A dual-band circularly-polarized double-layer U-slot microstrip patch antenna is proposed. The antenna is fed by a two-way Wilkinson power divider with different phase. The feed points are carefully chose to achieve a wide bandwidth. The antenna is printed on the substrate with high dielectric constant and simulated by HFSS and the simulation results are discussed. The impedance bandwidth (VSWR<1.5) of the lower band and higher band is 24.2% between 1.08GHz to 1.31GHz , and 5.7% between1.52GHz to 1.61GHz, respectively. The AR bandwidth (AR<6 dB) is 45% between 1.07GHz to 1.71GHz. The simulated results are in good agreement with the requirement of GPS applications.Index Terms-GPS, U-slot, dual-band, wide beamwidth.

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