Any way to build low cost police band Ka radar transmitter? NOT Jammer.

We are trying to curb speeders in the neighborhood, and I thought it would be cool to have one of those radar detector "tester" type devices.

Done a lot of research on this, but it seems it's hard to find a transmitter for the Ka band which would be the most beneficial to trick speeders into thinking they are being radar checked. I know jammers are illegal and frowned on in some places, so this I need just enough power to set off passing radar detectors. It can also use AC power or be fixed, since I'll just be using it around my house.

Thanks!