Ultra-Wideband Quasi-Yagi Antenna Using Dual-Resonant Driver and Integrated Balun of Stepped Impedance Coupled Structure

A quasi-Yagi antenna that has an ultra-wideband performance is presented. To enable that performance, the antenna utilizes a dual-resonant driver and a balun formed using a stepped-impedance coupled structure. The driver is designed to be dual-resonant by loading it with an inductor in the form of short section of narrow microstrip line at a certain position. The balun includes a T-junction of microstrip lines and two pairs of stepped-impedance coupled lines. The simulated and measured performance of the integrated antenna indicate less than -10 dB reflection coefficient, 3.6-4.5 dBi gain, 13-17 dB front-to-back ratio, less than -19 dB cross-polarization and more than 90% efficiency across more than 75% fractional bandwidth centered at 7.5 GHz.