Compact Ultra-Wideband Circularly-Polarized Weakly Coupled Patch Array Antenna

Abstract

A circularly polarized (CP) patch array antenna is proposed for ultrawideband operation by introducing weak-coupling mechanism into feeding network, feeding unit, and radiation structure, respectively. As an example, a wideband 2×2 patch array antenna consists of a weakly coupled-line four-feed network, a coupled feeding unit, and four weakly coupled sequentially rotated symmetric hexagonal patches is designed for verification. Measured results show that the proposed antenna exhibits the 10-dB impedance bandwidth of 98% (2-5.92 GHz), 3-dB axial ratio bandwidth of 96.3% (2.15-6 GHz), and 3-dB gain variation bandwidth of 82.5% (2.65-5.95 GHz) with the peak gain of 9.5 dBic at 5.15 GHz and the maximum efficiency of 88%. By the weak-coupling method, the design achieves not only the largest CP bandwidth and the symmetric radiation patterns without any beam squint over the whole band, but also the smaller volume of (1.13 × 1.13 × 0.15) λ <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> (λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> is the wavelength at 4 GHz) compared with the reported patch array antennas. Therefore, the proposed CP patch array antenna is very promising for modern wireless applications such as WiFi, global navigation satellite system, and radio frequency identification systems.