1. Introduction
Federal Communications Commission (FCC) granted the frequency band from 3.1 to 10.6 GHz for the purposes of an unlicensed use. While such a wide available spectrum is desirable for high-data-rate applications, it also puts high requirements on the RF front-enddesign, which considerably differs from the conventional narrow band system design. For the transmission of information, the IRUWB uses extremely short duration impulses (subnanosecond) instead of continuous waves. The impulse directly generates an instantaneous bandwidth signal according to the time-scaling properties of the Fourier transform relationship between the time and the frequency [1].