WIDEBAND WIRELESS SYSTEMS like Ultra Wideband (UWB) require antennas that are wideband and compact. One solution is a dipole antenna with folded elements, which is constructed by folding both ends of a folded dipole antenna to widen the antenna's bandwidth. Research into a simplified configuration has been performed in Kanagawa, Japan by Shingo Tanaka, Satoru Horiuchi, Yasunori Atsumi, and Yoichi Ido from Yazaki Corp.'s Microwave Technology Research Department together with Yongho Kim and Hisashi Morishita from the National Defense Academy's Department of Electrical and Electronic Engineering.
Their antenna, which folds both ends of a dipole for enhanced bandwidth, does not require a groundplane. As a result, it can be planar and more easily assembled. Using an electromagnetic (EM) simulator based on the method of moments (MoM), the researchers adjusted the parameter values in order to obtain wideband properties and compactness. In an experimental result centered at 1.7 GHz for 50-ohm impedance matching, the antenna boasts over 55-percent bandwidth with VSWR of 2.0:1 or better. The antenna delivered almost constant gain of 2 dBi across the band, with radiation patterns similar to a dipole.
The researchers made two prototypes of planar folded dipole antennas for impedance measurements. In the first one, the antenna employed an unbalanced feed, fed by a coaxial cable without a balun. The other had a groundplane for the balanced feed. The measured results agreed well for both. See "Wideband Planar Folded Dipole Antenna with Self-Balanced Impedance Property," IEEE Transactions on Antennas and Propagation, May 2008, p. 1223.