Square-ring microstrip antenna loaded with a center cross-shaped patch for compact circularly polarized radiation

By tuning a stub, the constructed square ring microstrip antennas loaded with a center cross-shaped patch for compact circularly polarized radiation are experimentally investigated. By adding a narrow stub in the square ring patch, it can perform a 90° phase difference and excite two near degenerate orthogonal modes. Circular polarization (CP) design from such a square ring microstrip antenna loaded with a cross-shaped patch, therefore, can be easily achieved. From the experimental results obtained: the size of the microstrip antennas, at a fixed CP operation frequency, is visibly reduced to be more than 33% of that of the conventional nearly square microstrip antenna