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In this paper, the utilization of a conducting spherical monopole radiator as a dual-band conical-beam antenna is investigated. The multi-band property is achieved by adding a quarter-wavelength slot (stub) and a conducting cylindrical ring for matching and bandwidth enhancement of the second operating band. The design is investigated and summarized based on numerical experiments or simulations. It is found that the proposed antenna provides a conical-beam with the impedance bandwidths (S11 less than -10 dB) covering two bands of operating frequencies, 2.4 to 2.5 GHz and 5.15 to 5.825 GHz. The best-matched values of S11 are about -21 and -16 dB for the first and second operating bands, respectively. Gains of the antenna are reasonably applicable, about 3.1 and 7.1 dBi at the centers of the two operating bands above. The far-field radiation patterns are of conical-beam type as required, with the main beams directed at the same 45-degree elevation angle for both operating bands. A prototype antenna has been successfully fabricated and most of the experimental results are agreed well with ones from the simulations. The investigation of this antenna also guides us that a quarter-wavelength slot may be further applied for other multi-band applications.