White Space Devices are seen today as one of the promising ways for easing the still worsening situation of congested spectrum caused by the growing number of users and the expectation of higher data transfer rates. Wideband communication techniques and frequency agility is needed to achieve flexibility instead of rigid frequency occupation structures. The pace of this progress, however, is going to be impeded by demanding requirements on the received and transmitted signal quality, introducing ultimate challenges on the performance of the RF analog frontend, such as in-band local oscillator harmonics, ultra low sensitivity and ultra high linearity. The RF frontend is thus likely to become the limiting technical factor in the realization of a wideband frequency agile transceiver system. As the application of such systems is commercial and high-volume, a CMOS solution is needed for the long run. In this book, the potential of CMOS technology is investigated regarding linearity and a novel, system-level approach for a frequency agile, highly linear and low noise high-IF upconverter frontend is introduced and implemented.