Look at the output bands it is operating on. See if you can detect the signal and use it to retransmit a false signal. After all, the radar is looking for a frequency shift (doppler) and a time shift (distance). Frequency shift can be easily done with a mixer, and time delay... Well, do you happen to have a lot of coax laying around?
Alternatively you can just see what happens by spewing wideband noise at it (ofcourse, do it in a shielded environment, even though the range at these frequencies is abysmal, you don't want to get into trouble). Even if they use narrow band filters, if you hit it with enough power to push the LNA into nonlinear operation, I suspect the performance will take a hit.
A lot of what you can do does depend on what equipment you have access to. What frequencies is this operating at? Mixers, oscillators, etc do not come cheap.