Prior to my retirement I, as part of a team, two engineers + HR, interviewed many (>100) people wanting to be NATS Engineers. The main failings which made us reject their applications were:
- Poor appearance, wear a suit, or a jacket, collar and tie or female equivilent
- Turn up on time
- Read up on what NATS does, makes you look as if you care
- Don't lie, it is mostly very easy to detect
- Then technical expertise
As for the radar question I would suggest going to Wikipedia and reading/understanding what is there. It is a very good question as it has a great deal of depth so the interviewers can sort the men from the boys, plus it gives candidates a vast area in which to dig themselves into holes. For example your reference to 'radar boxes' would be a good opening to find out what you meant by that phrase?