This paper presents a technique to design a very small planar antenna for ultra-wideband (UWB) communication applications. To cover UWB frequency range by a small-size antenna, the ground plane influence on the antenna impedance bandwidth is suppressed at middle and higher frequencies. To accomplish this purpose, a rectangular and several stepped slots are etched on the conventional radiator. Also, a tuning stub is printed in the rectangular slot, and its length is optimized. This technique decreases current distribution on the ground plane at higher frequencies, and the impedance matching of the antenna is significantly influenced by the radiating patch. The antenna has a compact size of 25 × 25 × 1.6 mm3. It can provide a wide impedance bandwidth from 2.8 to 15.4 GHz (|S11| < -10 dB) which covers the entire UWB spectrum (3.1-10.6 GHz). Two prototypes of the antenna were fabricated and measured. The impedance matching, group delay, fidelity factor, and the antenna radiation characteristics, including co- and cross-polarized far-field patterns and realized gain were analyzed with numerical simulation and experimental measurement. Measured data are in good agreement with the simulated ones. Based on the obtained frequency- and time-domain characteristics, the designed antenna is an excellent candidate for UWB wireless devices.
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