Efficiency improvement of mobile antenna by controlling ground structure

The proposed antenna structure with modified ground plane that fully covers Bluetooth and Wireless Fidelity (Wi-Fi) applications. In order to enhance the efficiency, a resonator which consists of a closed loop of a ground plane and lumped inductor (L) are proposed. The closed loop is connected to the ground plane with open-end extension by lumped inductor for easy control. This antenna designed on Flame Retardant Type 4 (FR-4) with 1 mm-thickness was used as the substrate (ε
_r
= 4.4, tan δ = 0.02). The overall volume of Printed Circuit Board (PCB) is 40 × 20 ×1 mm
³
and the size of a closed loop is 10mm × 20mm. A -6 dB bandwidth covering 250 MHz (2.38 GHz-2.62 GHz) is achieved and average efficiency of 69.05% is obtained in measurement. This technique is versatile and improves the antenna performances.