In this letter, a novel dual-band antenna covering 2.4/5.8 GHz Industrial Scientific Medical (ISM) bands is presented. At the lower band, a circular monopolar patch antenna with four symmetric slots is designed for omnidirectional radiation. At the upper band, a U-slot square patch antenna is designed for broadside radiation. By assembling the two antennas and feeding them with a common coaxial probe, the two resonant modes are preserved and the upper frequency bandwidth is broadened. A prototype is fabricated and measured. Measured bandwidths of 115 and 928 MHz and gains of 1.37 and 4.37 dBi are obtained at 2.45- and 5.8-GHz bands, respectively. The measured results agree well with the simulation, indicating that the proposed design is suitable for diverse wireless communication applications.