RadioBanter - direction finding antennas

On Sep 27, 4:33 am, happy wrote:
Hi,this is santhosh 7th sem BE.
we actually decided to do a local positioning system as our final
year project.But we got some comments about our projects that
directiionfinding is not an easy thing.so can u suggest some ideas to
accomplish this.

Lots can go wrong in RF geolocation systems, because of things like
reflections of the transmitted RF off other objects and trying to
resolve two or more sources on the same frequency. Some ways to
detect _direction_ include the already-mentioned Doppler systems,
systems where you detect the phase of the RF received at multiple
antenna elements (you gotta account for the mutual coupling of the
elements...), systems where you observe the maximum response of a
directional gain antenna (e.g. rotating a Yagi antenna), systems where
you look for the direction of a null (e.g. a loop antenna, sometimes
with a sense antenna to resolve the ambiguity of their "figure-8"
pattern that has two nulls, rotated till the signal nulls), and
systems that use the directionality of two or more antennas, using the
ratio of their amplitude responses to find a line of bearing (like two
loops at right angles, so you have two figure-8's at right angles; if
one antenna is nulled, the direction is aligned with the other
antenna's peak response; if you get equal amplitudes from both, the
line of bearing is mid way between the two...a sense antenna can again
resolve the ambiguity).

All of those give lines of bearing. To get geolocation, you need
something more, like a triangulation system where two or more lines-of-
bearing cross where the signal's coming from; or a system that
measures the difference of time-of-arrival of the same signal at
several different locations that are time-synchronized.

I'm sure you can find whole books on RF direction-finding and RF
geolocation.

Cheers,
Tom