While not an RF book per se, High Speed Digital design does a great job of spanning the gap from EE undergrad to the basics of RF as it relates to digital desig

While not an RF book per se, High Speed Digital design does a great job of spanning the gap from EE undergrad to the basics of RF as it relates to digital design. I'd also recommend brushing up on more advanced E&M, eg T{E,M} modes and antenna design if you haven't looked at them in a while