LAUSR

In this letter, a circularly polarized (CP) slot antenna with compact size is proposed for global positioning system (GPS) applications. An annular slot structure is adopted in this design because it inherently has two orthogonal degenerate modes, called one‐wavelength modes. Lumped capacitors are utilized so that miniaturized antenna size of 0.26 λ0 × 0.26 λ0 is obtained, but the axial ratio bandwidth (ARBW) is narrow because of high‐Q characteristics of the slot modes, providing a rapid change in phase difference near the operating frequency. Accordingly, an additional T‐shaped strip is implemented on the ground in the proposed design, which is known as ground‐mode tuning technique, to improve the ARBW. The T‐shaped strip provides a slower change of the phase difference between the two orthogonal slot modes, efficiently contributing to a greatly improved ARBW. The proposed antenna achieves a 3 dB ARBW of 50 MHz, which is over two times wider than that of the reference antenna. The operation mechanisms of the proposed antenna design are analyzed, and a comparison with typical slot antennas is discussed.