Abstract: The structure of Quasi Yagi antenna on Ramadan A. Alhalab's antenna is improved in this paper. The par asitic patches and coupling patches are used in this modified antenna to improve the bandwidth. The director elements at the back of the antenna are designed to improve the gain. In addition, the shape of feed network is amended to reduce the size of antenna. The relative bandwidth of the antenna is broadened by these design measures. The antenna is tested by the simula tion calculation of Ansoft HFSS and practical measurement. Results indicate that the structure of antenna is reasonable and its relative bandwidth is greater than 20%(VSWR 2)and its gain at 2. 4GHz is greater than 10dB. In a word, it has superi or performance. The range of application is broadened. The compact structure and small size is useful for the antennas ar ranged also.