12' antenna w/short elements attached

[RocketMan1]

I have been seeing these antenna's everywhere, they are about 12 feet tall with smaller (really small) elements, about 4-6, going around the top, sometimes the bottom. What is the purpose of these smaller elements? especially on top.
Also at a local school I saw a bunch of antenna's, but the one that caught my antention was what apeard to be a ground plane, mounted upsidedown. why would you do that?

 

[RocketMan1]

Here is a link to what I've been seeing, but the question still remains...what is the purpose of the elements on top?

http://www.diamond-ant.jp/ama2/eng_ama_2_6_2.asp

 

[LarrySC]

When you transmit you must simulate an earthen ground so the wave pattern is complete and the transmitted signal will push away from the antenna. The smaller elements are the simulated ground system. All AM/FM Broadcast antennas use the actual earthen ground to complete the wave pattern. With higher freq comms you cant communicate with the antenna on the ground so when you put it high into the air the small elements are the ground system for the transmitting antenna.

 

[RocketMan1]

Thank's for the explanation.

 

[ReceiverBeaver]

And there are yet more varieties. Some radial projections coming off of certain antennas are radiating elements for different bands. You'll see these on the old style Hustler mobile HF antenna for ham transmitting. Yet another style is a circular thingy around the very top of a mobile antenna and this is a capacitance hat, which again assists tuning capability particularly on like 80 or 160 meter ham mobile antennas.