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This letter presents a simple and innovative method for designing and optimizing two circularly polarized printed quadrifilar antennas (PQAs). The PQAs are operated at UHF RFID (902-908 MHz) and GPS (1575 MHz) and intended for use at a portable terminal. This new antenna system comprises two PQAs concentrically arranged, but electrically isolated. Each PQA comprises four inverted-F monopoles arranged orthogonally and excited with a phase difference of 90°.