I read it on hackaday, then again on G3XBM's blog: there is an easy way to play with 10 GHz. And (very) cheap too!! The idea is to repurpose something originally meant to be used as something else. Like the RTLSDR TV dongles, the 74HC240 buffer and many more in this wonderful hobby.
The HB100 is a microwave sensor module designed to be used as motion and speed (doppler) detector. It operates on 10.525 GHz and can be retuned below 10.500 GHz into the 3 cm HAM band (Italian bandplan) with a screwdriver. It can be frequency modulated through the power supply (I guess you get some AM too). It features both the transmitter and the receiver, (patch) antennas included.
How much? Less than 3 EUROs including shipping. That's three espresso coffees standing in an Italian bar. Or three of the cheapest burgers in the "M" restaurant (their own definition, not mine).
Drawbacks (A.K.A. "challenges"):
1) The RF power is in the order of 10 mW (10-12 dBm).
2) Frequency stability was not a design goal for the original destination of use
3) Receiver is direct conversion
I have ordered 2 pairs and a spare one. I am curious how far the unmodified version will go.
By the way, I have spotted a similar radar device operating on 5.8 GHz and others on 24 GHz (InnoSent IPM165). Maybe ... ?