A Low-Profile Broadband Circularly Polarized Metasurface Antenna Based on Tri-Modal
Chun Ni, Liang Zhang, Zhongxiang Zhang
Abstract
A low-profile broadband circularly polarized metasurface antenna with a single-layer substrate is proposed. The metasurface is composed of nonuniform truncated corner square patches arranged in two different arrangements. The central part of the metasurface is a 2 × 2 array, while the outer part is surrounded by an additional 16 unit cells. The antenna is analyzed using characteristic mode analysis, revealing that it can expand its impedance and axial ratio bandwidth by exciting three modes. At frequencies below 3.2 GHz, modes 1 and 3 are excited, with a characteristic angle phase difference of approximately 90° between them. However, above 3.2 GHz, modes 3 and 4 are activated, also exhibiting a characteristic angle phase difference of about 90°. The design is simplified, and manufacturing costs are reduced by placing the metasurface and the coplanar waveguide feed on opposite sides of the substrate. On this basis, a prototype antenna is fabricated and measured. The overall size of the antenna is 0.45λ<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub>× 0.45λ<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub>× 0.0067λ<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> (λ<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> represents the wavelength at the lowest operating frequency in free space). The measured results show a −10 dB impedance bandwidth of 66.7% [(2.47 to 4.94) GHz], a 3 dB axial ratio bandwidth of 75% [(2.0 to 4.4) GHz], and a peak gain of 5.5 dBi.