RIS-Based Compact Circularly Polarized Microstrip Antennas

Compact, asymmetricsymmetric-slottedslit-microstrip patch antennas on reactive impedance surface (RIS) are proposed and studied for circularly polarized (CP) radiation. The antennas consist of a slotted-slit-microstrip patch on a RIS substrate. The CP radiation with compact size is achieved by asymmetricsymmetric-slot-slit cut along the orthogonaldiagonal directions of the patch radiator. The asymmetricsymmetric-slottedslit microstrip patches on the RIS structure are used for further miniaturization of the antenna with improvement in CP radiation. The measured results of the compact asymmetric-cross slotted square patch antenna are 1.6% (2.51-2.55 GHz) for 3-dB axial ratio bandwidth, 5.2% (2.47-2.60 GHz) for 10-dB return loss bandwidth, and 3.41 dBic for gain over 3-dB axial ratio bandwidth. The overall antenna volume is 0.292λ_o × 0.292λ_o × 0.0308λ_o on a low cost FR4 substrate at 2.5 GHz.