A simple broadband circularly polarized (CP) aperture antenna is proposed in this letter. The antenna is composed of an L-shaped feed line and a circular aperture. With the newly introduced perturbation slots, a new resonant mode TE31 is generated, which can widen the CP bandwidth without increasing the antenna size. Measured results of the fabricated antenna shows 93.5% (2.9-8 GHz) impedance bandwidth (|S11|<-10 dB) and 66.6% (3-6 GHz) 3 dB axial-ratio bandwidth. The overlapped CP working band covers the entire WiMAX, WLAN and lower frequency 5G bands. Its peak gain is 4.9 dBic at 3.5 GHz, and its gain variation is less than 1 dBic within 3-5.8 GHz band. Design considerations, empirical formulas and surface current analysis are also presented and discussed.
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