I first started playing in SHF with 10mW Gunnplexer modules. I built a 10GHz beacon, a Doppler radar gun, and a pair of transceivers.
You can find the modules on ebay and other places, they're pretty cheap, they typically tune over several GHz mechanically, and a few hundred MHz electrically and are very simple to work with. They contain a microwave diode that oscillates at microwave frequencies when power is applied. Varying the supply voltage will change the frequency a bit. Better (more expensive) units have a separate tuning control input for modulation.
The great thing is a gunnplexer forms a mixer by using its own transmitter as a local oscillator. To make a radar gun, you just hook up an audio amplifier, or an audio frequency counter. When you point the gunnplexer at a moving vehicle, the outbound 10GHz bounces off the car at a slightly different frequency, comes back, and mixes with the original signal to give you an audio signal corresponding to the speed of the car. The tone is about 30 Hz per mile per hour as I recall.
The beacon simply keyed a gunnplexer with a tone modulated power supply and sent morse code. I could hear it 12 miles away on a mountaintop.
Making a two way communication system was harder. I offset two gunnplexers by about 30MHz, then used wideband 30MHz FM receiver boards to demodulate the gunnplexers. The hardest thing here is gunnplexers are not very frequency stable with temperature, so you have to use a wideband signal so you don't have to chase it all over the band. I made a line of sight voice contact over several miles with mine. I tried to send video over it, but I had trouble coming up with a modulator scheme that could handle the bandwidth required.
Lots of fun.