A sleeve monopole antenna, which has a wide impedance bandwidth for indoor base station applications, is successfully realized experimentally and numerically. The proposed antenna consists of dual sleeves, loaded circular disc and two shorted pins which are connected to the circular ground plane. The antenna possesses 14-dB impedance bandwidths of 30.3% and 46.5% at the lower and higher bands, respectively. And the 10-dB return loss bandwidth of the antenna is 128.2%, which is about 48 times that of the traditional monopolar wirepatch antenna. The antenna is successfully simulated, designed, and measured, showing dual-band and wide band characteristics, stable gain and good omni-directional radiation patterns.