Section 3.8 presented the problem of the radio frequency interference (RFI) environment in ultra wideband (UWB) radar operation from the standpoint of background clutter. This chapter will cover the significant design factors needed to operate a foliage penetration (FOPEN) radar, in either synthetic aperture radar (SAR) or ground moving target indicator (GMTI) modes, and under most operational conditions. Because of the worldwide regulation of the RF spectrum for telecommunications and active sensing operation, it is necessary to accommodate the limits that are imposed on power spectral density for transmission of the FOPEN UWB waveform. Equally as important is the need to remove the dense, high-power transmissions that will be intercepted by the wide beamwidth SAR antenna and that affect the dynamic range of the signal received by the SAR and the image formation processing.