Contents I. Introduction
In the last years Ultra Wideband (UWB) technology has been knowing a growing interest by the scientific and industrial community to enable new features in Radio Frequency Identification (RFID) applications. Some requirements, such as robustness to multi-path fading and reliable sub-meter localization and tracking, cannot be achieved by the already existent ultra-high-frequency (UHF) RFID systems, because of the narrow bandwidth limitation [1]. Passive, or semi-passive, UWB RFID systems based on backscattering modulation are very attractive because of the low energy consumption, low cost and simplicity of the tag with respect to the active UWB systems. The design of the complete passive UWB RFID system asks for a reliable UWB backscattering channel model in order to find the best trade-off between data rate, operating range and location accuracy. While a large number of contribution have been presented in literature on antenna backscattering [2]–[5] and UWB channel [6], the UWB backscattering channel has been poorly investigated. In [7] UWB backscattering channel has been characterized by considering a double convolution of the UWB one-way channel. Nevertheless the backscattering channel is strongly dependent on the tag antenna, which has to be considered for the real application implementation. Moreover one of the limiting factors to the UWB passive RFID systems could be the clutter by the environment, which has not been modeled yet.
