Compact circularly polarized microstrip antenna for GPS applications

A compact design of circularly polarized microstrip antennas is described. The antenna has a square-ring radiating patch, and it is excited by a feeding network consisting of a quadrature coupler with dual lumped capacitors and an impedance-matching circuit. The feeding network has a considerably smaller size than a traditional 90 degrees hybrid, and therefore, it is placed at the inner slot of the square-ring patch. By tuning the capacitance value of the lumped capacitors, the antenna can generate good circular polarization radiation. An antenna prototype designed for global positioning system applications is implemented. From the measured results, the 10 dB-return-loss bandwidth and 3 dB-axial-ratio bandwidth of the prototype are 3% and 1%, respectively. Simulation results obtained by HFSS are also provided to validate the experiment. (c) 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:1293-1296, 2014