Artificial neural network-based multiband μ-negative Hilbert curve fractal antenna using RSRR unit cell

An electrically small multiband planar antenna is presented by using rectangular split ring resonator (RSRR) metamaterial element for LTE, WiMAX and WLAN applications. The designed antenna possesses asymmetric coplanar strip (ACS)-fed Hilbert Curve Fractal Antenna (HCFA) loaded with RSRR metamaterial for multiband radiation at 1.44 GHz, 3.76 GHz and 5.27 GHz. ACS-fed HCFA is responsible for creating the first (at 1.44 GHz) and second (at 3.76 GHz) resonance frequencies owing to the coupling between ACS-fed HCFA and ground plane. Moreover, the RSRR yields upper resonance at 5.27 GHz owing to the metamaterial transmission line. The stop band and pass band nature of the RSRR and its negative permeability characteristics are described using an effective medium theory. An equivalent circuit model of the proposed antenna is investigated with the help of Agilent ADS to validate the operating frequencies. Also, the geometrical parameters have been optimized using the artificial neural network (ANN), which is performed by MATLAB. The proposed antenna has been fabricated on a 18 × 16.5 × 1.6 mm³ FR-4 dielectric having \({\upvarepsilon }_{{\text{r}}}\) ${\mathrm{\epsilon }}_{\text{r}}$  = 4.4 and \(\tan {\updelta }\) $tan\mathrm{\delta }$  = 0.02. It provides multiband response at 1.4 GHz, 4.4 GHz and 5.3 GHz with a − 10 dB impedance bandwidth of 330 MHz, 570 MHz, and 340 MHz, respectively, which is usable for LTE, WiMAX and WLAN band applications.