A compact triple-band metamaterial-inspired antenna for wearable applications

A low-profile (28 mm x 32 mm x 0.394 mm), metamaterial-inspired antenna employing an array of 3 x 5 Hilbert-shaped unit radiators printed on the upper side of a flexible dielectric substrate while the lower side contains a partial-ground plane and the rest consists of a periodic square-slotted ground plane is presented for wearable wireless devices covering Long-Term Evolution (LTE), Long Term Evolution-Advanced (LTE-A), Wireless Local Area Network (WLAN), and Worldwide Interoperability for Microwave Access (WiMAX) bands. The antenna provides steerable radiation patterns for frequencies ranging from 3.3 to 3.9 GHz and a directive end-fire radiation in the 5.8 GHz band. At 2.45 GHz, the antenna allows short-range communications between a wearable sensor and handheld wireless device or a nearby base station. Two prototypes are fabricated; the first using traditional wet etching with copper; the second using inkjet printing with silver nano-particles (SNPs) as the conducting material. We provide a systematic design procedure and a new physical insight into the operation of the antenna, in particular the end-fire radiation patterns, which is based on the anisotropic dispersion characteristics of the radiating structure along the length axis leading to different effective electrical length to width ratios within the stopband. The realized gain varies from 0 to 2.5 dBi for frequencies ranging from 3.3 to 3.9 GHz where the 3-dB beamwidth varies from 110 degrees to 140 degrees and the boresight is steered from 0 degrees to 80 degrees. The maximum realized gain varies from 4.75 to 4.5 dBi over the frequency range from 4.4 to 6 GHz, with slight change in the beamwidth and main lobe direction. Experimental measurements for the SNP prototype are reported in air and on a standard phantom model.