A low‐profile (28 mm × 32 mm × 0.394 mm), metamaterial‐inspired antenna employing an array of 3 × 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° to 140° and the boresight is steered from 0° to 80°. 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.
Abstract:A flexible (2 × 1) multiple-input, multiple-output (MIMO) antenna with an electromagnetic band gap (EBG) unit cell is designed and measured. The proposed MIMO antenna is based on a circular slotted patch antenna to work at 3.5 GHz. An EBG unit cell is used to reduce the effect of the inherent mutual coupling produced between the closely spaced MIMO elements. The results show that the measured mutual coupling has been reduced by -11.6 dB (from -10 dB to -21.6 dB), and the measured realized gain has been increased by 1.074 dBi (from 1.59 dBi to 2.66 dBi). An improvement by 2.4% in the simulated efficiency was also noticed (from 78.7% to 81.1%). The proposed antenna also passed the flexibility test without a noticeable change in the S-parameter at the desired frequency.
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