In the original UFO, the ufo:s were simulated and flew around the planet even if your radar stations didn't see them.
However, there was one more way to spot an ufo and that was to fly around with your aircraft and hope to cross the path of one, since they had a small, built-in radar.
I was fanatical in doing this, patrolling day and night, and I encountered quite a number of ships this way. It wasn't much fun with the relentless clicking though.
I'm sad to see that Xenonauts have not improved on this part of the game. The obvious route would of course be to add a "Patrol" action in addition to the "Intercept".
My proposal would be that this would allow you to setup regular radar sweeps of a particular area (country) of interest and get rid of the tedious clicking.