Compact, Printed, Tri-Band Loop Antenna With Capacitively-Driven Feed and End-Loaded Inductor for Notebook Computer Applications

Abstract

The shorted monopoles and the planar inverted-F antennas have been utilized for wireless local area network (WLAN) notebook applications for years. This paper presents an alternative and yet promising antenna type with a compact and smaller size of 5 mm $\times20$ mm to operate in the 2.4 GHz (2400–2484 MHz), 5.2 GHz (5150–5350 MHz), and 5.8 GHz (5725–5825 MHz) WLAN bands. The loop antenna, formed on a 0.4-mm-thick FR4 substrate, was adopted in this study. The loop radiator comprised a capacitively-driven feed and an end-loaded inductor. The capacitively-driven feed allowed the antenna to generate the quarter-wavelength loop resonance for possible lowest resonant mode excitation in addition to the loop’s half-wavelength mode. By loading an inductor at the loop end to be connected to the small antenna ground, the operating frequencies of the quarter- and half-wavelength resonances were further decreased to cover the 2.4 and 5.2/5.8 GHz bands with good input impedance therein.