A single-layered ultra-wideband circular patch antenna with monopole-like radiation patterns is presented. In this letter, the geometry of the proposed antenna is described initially. Then, in order to indicate the working mechanism, the design process is demonstrated. By etching ring-shaped slot around the feeding point and introducing shorted parasitic ring patches, multi-mode resonance is implemented in the operation band. The impedance bandwidth is effectively enhanced and the ultra-wide bandwidth can be achieved. Finally, prototype is fabricated and measured. Experimental results illustrate that the proposed antenna has an operation band of 3.3-10.1 GHz (101.5%), a stable gain about 4 dBi over the band, a low cross-polarization level of about -20 dB and stable omnidirectional patterns in its end-fire radiation. Depending on these merits and its low profile, the proposed antenna is suitable for indoor base station application.