A Quad-Fed Triband Circularly Polarized Patch Antenna Based on Three Resonant Modes

A quad-fed triband circularly polarized (CP) patch antenna based on three resonant modes is proposed in this paper. This antenna consists of a square patch loaded with an open cross slots, two pairs of arc slots, and four shorting pins. The acquisition of the three bands is attributed to the simultaneous excitation of TM₁₁ mode of circular patch, TM₁₀ mode of square patch, and the one-wavelength cross slot mode. The TM₁₁ mode of circular patch is excited by the cooperation of the arc slots and the shorting pins, while the loading of the open cross slot moves the TM₁₀ and TM₂₁ modes of the square patch to a higher frequency. Furthermore, the introduction of the arc slots improves the impedance matching of the one-wavelength cross slot mode. The equivalent circuit of the proposed quad-fed patch antenna is established, and its validity is verified. For implementing CP radiation with the same sense in all three bands, a sequential phase feed network is designed and cooperated with the antenna. In order to verify the design concept, an antenna prototype is fabricated and measured. The measured results show that the VSWR is less than 2 in 2.54–5.5 GHz, which can cover the three frequency bands of the proposed antenna. The AR bandwidths in three bands are 33.1%, 27.6%, and 8.6%, respectively. The peak RHCP gains in the three bands are 5, 9.9, and 4.1 dBic, respectively. The profile is 0.032λ₀ (λ₀ is the wavelength in the free space at 3.2 GHz).