A Wideband Circularly Polarized 2 × 2 Patch Antenna Array

In this study, A wideband circularly polarized 2 × 2 patch antenna array with wideband broadside radiation characteristics is proposed. The proposed array consists of four circular patches rotating in sequence, and each patch is loaded with an inclined rectangular slot. The purpose of adopting capacitive coupling feed is to excite three resonant modes of circular patch at the same time. The wideband property benefits from the combination of three modes, namely TM_2, 1, TM_2.5, 1, and TM_3, 1. The improvement of circularly polarized gain on the broadside is attributed to the compensation of slot mode, which has natural broadside radiation. The proposed 2 × 2 antenna array employs the layout of sequential rotation, meanwhile the phase conditions required for circularly polarized radiation are met by designing a one-to-four power division and phase-shifting feed network. To validate the array design concept, a prototype is fabricated and measured. The measured results indicate that the fractional bandwidth of VSWR < 2 is 66.7%, involving 5–10 GHz, while the relative bandwidth of AR < 3 dB is 53.1%, involving 5.17–8.91 GHz. Besides the realized RHCP gain is larger than 6 dBic in the band of 5.35–8.86 GHz, and the relative bandwidth is 49.4%. The peak gain is 11.5 dBic and the radiation efficiency is 72%–88% within gain bandwidth. The antenna profile is 0.125λ₀ (λ₀ is the wavelength in free space at center frequency).