Wideband Circularly Polarized Stacked Patch Antenna Based on TM₁₁ and TM₁₀

A wideband circularly polarized (CP) stacked patch antenna based on TM
₁₁
and TM
₁₀
is proposed in this article. This four-port antenna consists of a circular patch and a square patch, where the square patch is located above the circular patch. Taking into account the mutual coupling between four ports, the active reflection coefficient (ARC) is adopted to describe the impedance matching of the antenna, and a simplified form of ARC is derived. The abnormal electric field distribution generated in the square patch is attributed to the superposition of the electric fields of two orthogonal TM
₁₀
modes, which is theoretically verified. Due to the coupling between TM
₁₁
mode and TM
₁₀
mode, a new resonance mode appears in a square patch, where the abnormal electric fields on the two diagonals are generated simultaneously. The effect of the square patch on the circular patch is equivalent to a capacitor at the lower frequency end and the higher frequency end of −10 dB impedance bandwidth, while it acts as an inductor at the middle frequency band. Besides the horizontal patch of
$\lceil $
-shaped feed is sandwiched between two radiators to enhance coupling. Finally, a wideband feed network composed of Wilkinson power divider and phase shifter is devised to provide four signals of equal magnitude and quadrature phase for proposed antenna. To verify the design concept, a prototype is fabricated and measured. The results show that left-hand circularly polarized (LHCP) radiation is achieved. The 3 dB gain variation bandwidth is 44.6%, ranging from 1.48 to 2.33 GHz, in which VSWR < 1.5 and AR < 1.5 dB. Besides the peak gain is 9.5 dBic and antenna efficiency is not less than 64%.