In this paper we present a microstrip patch excitation technique through electromagnetical coupling in a single layer able to generate broadband circularly polarized (CP) radiation. The circular polarization operation is obtained by simply adjusting the feed system dimensions without modifying the microstrip radiator. The proposed feed technique also has the advantage of being applicable to any regular polygon; in this case, its operation is validated experimentally for a square and an ellipse. From the simulation results a 3-dB axial-ratio bandwidth of 100 MHz (4%) and 110MHz (4.48%) are obtained, respectively, relative to the center frequency of 2.44 GHz, making the designed antennas an interesting solution for applications such as RFID readers, or communications in ISM band.
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