Operating principle and design approach of a novel dual-band aperture-dipolecomposite antenna are proposed. It is shown that multiple operating modes can be simulta-neously excited by employing offset-feeding technique at first. After the behavior of eachmode is studied, the operating principle of the antenna is analyzed and described. Then, animproved dual-band aperture-dipole composite antenna is formed and it is designed byusing the proposed approach. The antenna is experimentally verified. It is demonstratedthat two operating bands for radiation are ranged from 2.36 to 2.58 GHz and from 4.1 to15.72 GHz, respectively, in which the reflection coefficient are both<210 dB. The averag-ing gain of the antenna is about 4.5 dBi with good flatness across both bands. The proposedantenna is useful for promising dual-band wireless/mobile systems.