This letter presents a low-profile wideband circularly polarized (CP) patch antenna with a single layer of dielectric. An asymmetric inset is incorporated in the antenna structure using two parallel slots, each containing a patch, with a length difference of lambda(eff)/4. The length difference leads to a 90 degrees phase difference between the currents on the left- and the right-side patches, causing the antenna to radiate a CP wave. Additionally, a broad bandwidth is achieved because of the additional resonance point generated by a quarter-wave resonance from the asymmetric inset. The proposed antenna achieves a peak gain of 7.4 dBiC and fractional bandwidths of 17.2%, 15.1%, and 13.3%, respectively, for -10 dB S-11 bandwidth, 3 dB gain bandwidth, and axial-ratio bandwidth with a single-dielectric-layer structure.