I'd imagine a parabolic dish that points at the satellite, driven by something powerful like a klystron. With a highly directional antenna and high power one should be able to saturate the satellite receiver.

That's what L3's published images look like. A dish on a trailer that can be moved to wherever it's needed. It's an antenna that's producing (mostly) high-powered noise while pointed at a target satellite. Probably configurable like an ordinary antenna to make it mission specific and take advantage of known weaknesses in the target system.