Most people will be unfamiliar with notch/slot type HF aerials, because they're generally invisible under the paint.
For some unknown reason the HF slot aerials on the Concorde prototype 002 were never painted over, so this photo at least gives an idea.
An amusing detail, which illustrates the amount of HF current in the surrounding structure...
During the first in-flight tests of the HF, Concorde "wagged its tail" whenever the HF was keyed.
After some detective work, it was found that the yaw rate gyros inside the tail picked up enough HF to disturb the yaw autostabilisation system and generate spurious rudder commands.... A few filters in the right spots solved that one.