Thinking after market as I could'nt find any cars with one,,ridiculously big fin,still has the mounting gaskets and never used,,maybe something 50's ??
Those exact antennae came in early AMT 3 in one kits when I was a kid, circa '58-9, so that's a date point. I don't think I ever saw any full-size ones in use!
You've just gotta find another one and mount them on each rear quarter panel jus behind the rear window! And chrome-plating them would be a plus!
Two cars of the fifties had the big finned antennae: The '57-'59 Dodge (I found several pics of 2 dr hdtps and convertibles with twin, big-finned antennae in the book Cars of the Fabulous '50s) as well as the '57-'59 Rambler, which had a big finned antenna in the middle of the deck lid (same book as above). The smaller finned, red plastic antenna is likely a '55-'56 Ford accessory antenna and they are repopped for about $75.
I have a stock unrestored 1956 Studebaker President with a pair of these mounted on the top of the quarter panels.
Found it last night...I was rummaging through old HRM's and found a JC Whitney catalog in the stack. 1963 edition...exact match to one shown above. Listed as "Shark Fin" antennas, available singly or in pairs, dummy or functional. "Newly styled to add glamor as well as powerful radio reception to any car...blah, blah, blah... Prices ran from $2.98 for a single dummy to $8.75 for a functional pair. Great catalog...I want "Winky the Cat", everything in the hotrod section, about half the schlock custom bolt-ons, some of the tools, and maybe three 59A's @ $83.50 from the used parts section, "selected used complete motors in good running condition...".
That's not an antenna, that's a VERTICAL STABILIZER. Make sure you mount it straight, or your car will be constantly turning in circles.
I have a match to the one above in a box at my shop if someone decides to run it. Mine is a dummy, it doesn't have the hookup for the cable like this one does. probably made to be used as a pair but only one functional. Or I'd buy the one shown above if it was cheap enough just to have a pair.
I tried to make my own repro Winky the Cat, but the little ******* practically clawed my face off before I even got the bulbs mounted. Apparently cats HATE electronics.
Looks aircraft to me - especially the connector. Perhaps JC Whitney were selling surplus antennas back in the day...