Ok, I figured it out myself, on a different page here; the smaller antennae's main posts have prongs at the bottom inside the black cylinder that you can't see. They release themselves if you pull up perfectly vertically. I recommend using four fingers two each on opposite corners, and other fingers to push against the drive and chassis to ensure your pressure is vertical, and pull straight up. Be careful, I'm sure it's easy to break the boards or posts with any angled force.
the smaller two antennae in my mini do not have the two black locking posts like the larger one in the picture. Would somebody please describe how to release the smaller antennae from the sprung posts that mount them? Thanks.