This is an X band Gunn Diode Oscillator.  It has a tuning screw for coarse adjustment and an AFC electrical tuning capability for phase locking, adjustment and sweeping.  The Pin labeled as Gunn Power is where you put in the nominal 3 volts through a resistor to the pin to power up the oscillator.  It is untested but believed to be working due to its being excess unused inventory.

Actual part number = MAH765H  ( I believe this is an old Microwaves Associates part number)

I have several of these. Inquire. Asking 30$

WARNING: Please note that you should not power this up while you are in your car.  You will most likely set off other peoples radar detectors and they would incorrectly think that a police traffic radar is scanning them.