Compact and printed, coupled-fed, 2.4 GHz loop antenna

A novel, coupled-fed loop antenna with a small form factor for wireless local area network (WLAN) operation in the 2.4 GHz band is presented. The antenna has a very compact structure with the dimensions 29.75 mm × 5 mm and consists of a half-wavelength loop and a coupling feed, all printed in a coplanar configuration on a 0.4-mm thick FR4 substrate. The antenna was easily fed by using a 50-Ω mini-coaxial cable, allowing it to have much flexibility in the placement in a defined location. The results show that good input matching over the 2400-2484 MHz band can be achieved by tuning the coupling-pad size and the loop width. Good omnidirectional radiation patterns were also observed. Details of a design prototype are described and discussed.