One example is antennas used for animal tracking. These would normally be attached to a VHF or UHF transmitter. The antennas need to be inconspicuous and not harm the animal's life or movement.
Here are some items on antennas (and transmitters) for animal tracking you might find interesting:
* Wikipedia item on wildlife radio telemetry
* Telonics . com product range of tracking devices
* ATS Systems Australia animal tracking
* Perdix radio tracking tags
* Biotrack radio telemetry
* Use of UHF modules for animal tracking (pdf)
Have you used any of these? Or even built some? Please let me know your experiences below.