It was done by phone back when I interviewed but is probably by zoom today. I was pasted around to different groups within the organization. You do a series of interview and they ask if you are interested in their group. If you say yeah they will then ask a bunch of technical questions I found rather varied and tough due to the many different group/people involved. This was entry-level and I, by good fortune, found a group who asked question that I correctly reasoned through.

Know your circuit analysis, they will ask you technical questions. This place is highly technical and if you lie on the answers during the interview they will know it. My interview was a very large panel of supervisors and what seemed like technical experts.