I am puzzled as to your actual requirement. Explanations and descriptions
of the techniques and hardware to do what I *believe* you are asking have
been published for years in innumerable journals and magazines. One
specific application which comes to mind is the location of VHF/UHF ELT
transmitters inside a hangar where they have been accidentally activated.
Those are described in various flying publications. Real challenge inside a
reflecting metal hangar where the transmitter might be in any one of a half
dozen aircraft, and the signal appears to be stronger out in the middle of
the room than near any of them. There are articles about amateur radio fox
hunting (HF, VHF, MF) hardware published in all the English speaking
countries I am aware of, and I see references to articles in many other
languages as well. Just out of curiosity, I did a Yahoo search (based on
your Yahoo reference) and found commercial products, references to many
literature articles, construction plans, and other indeterminate citations.
I used VHF, radio and "direction finders" as the search string. Maybe one
of the problems here is that looking for a "DF antenna" is a fruitless
search. It has to be a complete DF system to perform any useful function.
Almost any antenna can be used as a DF antenna with appropriate support
electronics. The big elephant cage DF antennas (FLR-9, FRD-10) use simple
vertical monopoles as the actual antenna elements, but the system is much
more complicated than that.

--
Crazy George
Remove N O and S P A M imbedded in return address