A miniaturized, broadband quasi-Yagi antenna utilizing a modified ultra-wideband microstrip-to-coplanar stripline (MS-to-CPS) balun is proposed. Excellent broadband phase and amplitude balance is possible due to the ultra-wideband MS-to-CPS balun based on field and impedance matching concept. The implemented antenna provides very wide bandwidth from 7 to 15.1GHz (73.3%). The gain of the antenna is from 3.7 to 5.5dBi, the front-to-back ratio is more than 10dB, and the nominal radiation efficiency is about 94%.