A quad-band fractal antenna with metamaterial resonator-backed ground for sub-6 GHz, C and X band applications

This article proposes the design and analysis of a quad-band fractal square monopole with complimentary split ring resonator-backed ground plane. The metamaterial characteristic is responsible for improving the bandwidth of monopole antenna. The antenna operates at 4 microwave frequency band (4.43-4.57 GHz), (5.80-6 GHz)/sub-6 GHz band, (6.97-7.36 GHz)/C band, (7.89-8.18 GHz)/X band. Though quad-band is achieved with CSSR ground plane, fractal geometry inspired by Chinese coin-like structure improves impedance matching at the desired sub-6 GHz, C and X band. The prototype 50 x 50 x 1.6mm(3) is manufactured on a flame retardant 4 substrate with dielectric constant 4.4 and loss tangent 0.002. The antenna covers the impedance bandwidth of 130 MHz(4.43-4.56 GHz), 180 MHz(5.79-5.97 GHz), 390 MHz(6.9-7.29 GHz), 280 MHz(7.91-8.19 GHz) with a resonance frequency of 4.50 GHz, 5.88 GHz, 7.08 GHz, 8.06 GHz, respectively. The antenna has low reflection coefficient, good impedance bandwidth and radiation pattern for the desired application. The current distribution in patch is studied with characteristic mode analysis. Moreover, the equivalent circuit of the antenna is extracted using Foster representation. The CSRR equivalent circuit is discussed using quasi-static analysis, and the negative permittivity of CSRR is extracted using Nicholson Ross weir method.