Compact, High Gain, And Wideband Circularly Polarized Non-Uniform Metasurface Antenna

Abstract

Incorporating the metasurfaces in antennas are desirable as these increase the performance matrices such as impedance bandwidth, axial ratio bandwidth, gain, and radiation efficiency. Apart from these performance matrices of antenna low profile feature is also desired in many applications. However, keeping the low-profile nature of antenna with such high-performance parameters is a challenging task. To address this challenge, a new type of non-uniform metasurface has been designed that is characterized as high impedance surface. The unique feature of this high-impedance based metasurface is that it reflects the incoming electromagnetic waves in-phase, thus allowing the surface waves to be utilized constructively. This in-phase reflection of surface waves consequently results in improving antenna performance matrices. By designing an appropriate feeding network, surface waves in the designed metasurface are excited by the unit cells to generate extra resonances and confined radiation patterns. The radiations through unit cells are realized by the forbidden frequency band possessed by each unit cell. The designed metasurface is a 4x4 array of continuous metallic patches i.e., unit cells, in which each unit cell exhibits different resonance frequency by having non-uniform slots that are cut from the inner section of the unit cells. Moreover, the corners of each unit cell are cut diagonally to achieve circular polarization. The design analysis of the proposed metasurface is made by the floquet port theory. The proposed non-uniform metasurface exhibits multiple resonances, that are verified by the characteristic mode analysis (CMA). This non-uniform metasurface allows to excite surface waves by the help of slot antenna, having L-shaped microstrip feedline. The L-shaped microstrip feedline is designed to achieve improved impedance matching between feedline and the slot. The designed approach of metasurface-based antenna is kept simplified, that provides easy fabrication while exhibiting a peak gain of 9.35 dBi at 7.33 GHz, |𝑆11|≤ −10 𝑑𝐵 bandwidth of 48.84%, and −3 𝑑𝐵 axial ratio bandwidth of 19.92%. The proposed design is extended to realize a 4x4 metasurface-based array configuration to achieve further improvement in antenna’s gain and axial ratio bandwidth. This antenna array is excited by the sequential phase feed (SPF) network, which increased the -3dB axial ratio bandwidth up to 61.75% (4.50-8.52 GHz), with a peak gain of 14.45 dBi at 7 GHz. The comparison with literature is presented to give detailed insight about the proposed work. The presented antenna can be utilized for the applications related to wireless communication systems, long range tracking, weather observation, radar, and satellite communications, where wide bandwidth and high gain are desirable.