Ambiguity in the definition of ultra-wideband microwave imaging systems´ resolution

Utilization of the pulses with ultra wide frequency band (UWB) in microwave imaging systems enables obtaining great resolution and simultaneously taking benefits from the microwaves´ penetrating ability [4], [16]. Short duration of the pulses - which is what causes their wide frequency band - has also this advantage that it gives opportunity to perform time analysis and eliminate many unwanted signals, simply on a base of their time of arrival (when significantly different from the time of arrival of the signal of concern [13]). Known of UWB pulses is the fact that their shape is easily changed due to the convolution with pulse responses of the transmitter and receiver components [3], [21]. Antenna is here a recognized bottle neck [1]. However, this problem is possible to be mitigated by using better antenna or one of deconvolution techniques [6]. This paper identifies a problem with definition of the resolution of such imaging system. It is demonstrated that the pulse response of the object itself is also convoluted with measurement UWB pulse. Therefore, the resolution of the image of the object depends on the shape and dimensions of the object, what makes its definition rather ambiguous.