Probe-feed circularly polarized square-ring microstrip antennas with thick substrate

The design of a circularly polarized square-ring microstrip antenna fabricated on thick foam substrate and excited by a coaxial probe is proposed. To achieve 50 Omega impedance at the antenna input port, an L-typed matching network is formed by coupling the series probe inductance to a parallel capacitance introduced by adjusting the inner slot size of the square-ring patch. Simulated results are first used to indicate the designs of the key parameters for the proposed antenna. Follow by fabricating and measured several prototypes of the square-ring microstrip antennas with various foam thicknesses, their CP performances are illustrated and discussed.