You have many fields to use microwaves, some of them are:
- Communications (of course), its the future becouse it is the best way (now a days) to transmite signals. (phone, TV,...)
- Radars. Very important for army or just for police. Are in constan investigation for better radars.
- Power transmition. Well, these field is very theorical, but could be the best way to generate energy anywere and transmite it wirless with less losses
- There is something that is the future and there are many people investigating it, is the radas for cars and alarms. These antennaes are very small and thin, as thin as possible to put it in a PCB. With just those antenna and a properly wave generator you can situate the car next to you or the thief in the space (I mean, in a position) and also give you the velocity and direction of it movement.
(Hope you can understand my horrible english)
If you are interesting in the last thing, post it and I will give some interesting links.