A Defected Ground Structure for Circularly Polarized (CP) Microstrip Antenna Design

This paper presents a single-feed circularly polarized (CP) microstrip antenna achieved by defected ground structure. With the proposed DGS, a new resonant mode is added, which is orthogonal to the original resonant mode. These two modes will have the same magnitude and the 90° time-phase difference by adjusting the DGS dimensions, which contributes to achieve the CP radiation. Both the simulated and measured 10-dB impedance bandwidth of the CP microstrip antenna are 30 MHz, while the 3-dB axial-ratio bandwidth is 6 MHz. The CP gain across the 3-dB AR band ranges from 4.6 to 5.0 dBic.