I have been working in the microwave/mmW space for my entire(short) career and disagree on the boring side of civilian design.
As an electronics engineer specialized in microwave technology you can work on anything from new waveform designs for 5G, to hardware for these platforms or DSP algorithms for predistortion, advanced waveforms, low latency applications etc. There is an entire branch of specialized products for high tech industries, or maybe test and measurement is also an option, are particle accelerators something you would like to get stuck into, there is always demand for talent there! In the last 5 years mmW technology went main stream and you have a chance to ride the wave of car radars on these frequencies or maybe get a shot at designing 10G mmW front ends!
I would say that all of the options mentioned above are exciting and offer a good position for a life long career in microwave technology while being on the edge of what is being developed. I missed a whole load of different branches and opportunities that lay in wait for young people that want to venture into the microwave world.