The words "in visions" mean that this experience is happening in Ezekiel's thoughts. His body would still be in his home while God shows him these things.
"the inner northern gate of the temple." The temple was surrounded by two walls, one inside the other. This gate was on the north side of the inner wall. (See: [[rc://en/ta/man/translate/figs-explicit]])
Possible meanings are 1) "who looked the same as what I had seen in the vision that I saw when I was on the plain" or 2) "who looked the same as what I saw when I was on the plain."