This work focuses on UWB for cluttered wireless sensor network (WSN) applications, especially antennas design. In this paper, we present a novel planar small ultra-wideband (UWB) micro-strip fed antenna, for IR-UWB. Cluttered WSN are difficult cases for communications, implying the antenna to be adapted to the communication channel. The first consideration is the path loss compensation hypothesis. The designed antenna has a small size of 20x20x0.8mm 3 , and an omnidirectional radiation pattern over the frequency band considered (6-8.5 GHz). A comprehensive characterization of the antenna is done in both frequency and time domain. Thus, different path loss orders are considered and two signal pulses are used. The effect of channel path loss is discussed and the antenna transfer function is determined. Return loss and radiation pattern are depicted and completed with the isotropy factor. The gain increases with frequency, providing a quasi-constant free space transmission channel transfer function. Time domain analysis, via Fidelity factor and pulse width Stretch Ratio, is done for the both pulses and for the different path loss orders. Such Figures of Merit (FoM) are discussed in function of the path-loss order, which is a simple modelization of cluttered WSN channels (reference cases). Keywords—impulse radio ultrawideband (IR-UWB); wireless sensor network (WSN); UWB antenna; antenna transfer function; fidelity.