A simple planar circularly polarized antenna for GPS system

The design of a planar right-handed circularly polarized (RHCP) antenna used for the Global Positioning System (GPS) is presented in this paper. The antenna consists of two meandered monopoles, a feeding network designed using the Wilkinson power divider and a defected ground structure (DGS). These two meandered monopoles resonate at about 1.575 GHz and are placed perpendicular to each other. The Wilkinson power divider divides the input signal into two signals with equal amplitude and phase. A phase difference of 90° between the signals to the monopoles is simply achieved by using a difference in length of λ_g/4 (λ_g is the guide wavelength) in the two feed lines. The DGS is used to increase isolation between the two monopoles. Measured results show that the antenna has an impedance bandwidth (for reflection coefficient S11<;-10 dB) from 1.12 to 1.85 GHz and an axial-ratio bandwidth (for axial ratio AR <; 3 dB) from 1.53 to 1.66 GHz in the GPS band. The simulated and measured S11, AR, radiation pattern, efficiency and gain are presented.