The antenna is extended and retracted by a nylon cable wound on a spool. Breakage of the nylon cable is pretty common. Breakage of the antenna mast in a car wash is also common. In either case, here's how to fix it. The mast and nylon cable assembly costs a bit less than $20 from an aftermarket shop (see the Links and Info page for suggested New Parts suppliers).
Sorry, no pictures; I didn't have the camera with me when I did this repair. It's pretty easy though.
First, with the ignition and radio off, remove the nut that holds the antenna mast tube to the fender. Pliers will do fine; just take care not to scratch the paint.
Now, turn the ignition to standby, such that the radio can be powered, turn on the radio, and get back to the antenna to catch it as the cable is ejected. Pull the cable out.
If your repair is due to a bent antenna mast, then installing the new one is really easy. Just put the nylon cable into the antenna tube, turn off the radio and feed the cable in as the motor retracts it. It may take a couple of cycles to get it to catch and take up properly. If it sticks anywhere along the way, hose the mast down with silicone spray.
More likely is that your old cable broke off. If the cable on the old mast is shorter than the one on the new mast, then that means that a remnant of the old cable remains on the spool. In that case you'll have to do some disassembly and remove the old cable fragment, but it isn't too hard.