Ultra-Wideband Circular Microstrip Antenna with Hybrid EBG for reduced SAR

Abstract

This article presents a basic ultra-wideband circular microstrip antenna (UWB-CMSA) with partial ground resonating from 2.38 GHz to 12 GHz for handheld devices. The designed antenna covers bands for Bluetooth (2.4 GHz), LTE (2.5/2.69 GHz), WLAN (2.4/3.5/5 GHz), and WiMAX (2.5/3.5/5.5) GHz applications. Specific Absorption Rate (SAR) values of certain bands exceed a limit for UWB-CMSA. The uniplanar spiral unit cell is designed and exhibits phase reversal for 2.4 GHz, 3.5 GHz, and 5.5 GHz. EBG unit cells are placed near the feed for surface wave minimization so as to achieve a reduction in SAR. Furthermore, the EBG structure is placed on the ground plane to analyze the impact, also designs are fabricated and results are compared. Mushroom type M-shaped unit cell is designed which offers phase reversal at 2.3 GHz which is placed near feed in a similar fashion to the earlier spiral one to suppress surface waves also the structure is investigated by arranging it on the ground plane. It is evident that SAR is reduced for all the cases being inspected but for certain bands it exceeds the limit of 1.6 W/kg. A combination of two different unit cells to form a hybrid EBG structure is proposed and evaluated by placing it near the feed. SAR is curtailed by 87.05% at 5.5 GHz.