Electronic – Measuring direction of object (or angle of signal origin)

RFsensorsignaltransmitterwireless

I am interested in somehow tracking the "compass" direction of a moving object from a reference-station — in other words, something similar to submarine sonar systems (although I'm unsure how those determine the angle/direction of the target).

Note that I only need the direction/2D-angular-position of the object, and don't care about its actual distance/spatial-position. So, I wish to know, e.g., the object is at South 45° East from the reference-station.

Some notes:

  • Maximum size of circuitry at moving object: 10 cm X 10 cm
  • Maximum size of circuitry at reference station: 15 cm X 15 cm
  • The angular measurement needed is a relative one (i.e., as measured from the reference-station), not an absolute one.
  • An accuracy of +/- 10 degrees is more than good enough.
  • Measurement/tracking rate can be once per second, but faster wouldn't hurt!
  • While this tracking is being done, the moving object might be between 3 meters (min) to 100 meters (max) aerial distance away from the reference-station.
  • Assume that cost is not critical and that both the object and the reference-station can be electronically equipped (i.e., with sensors/receivers/transmitters/etc.)
  • The object and the reference-station will be located in an outdoor/urban environment.

What technique could I use to get started on achieving this kind of direction measurement/tracking?

I've considered using standard wireless signal transmission, but with this, I've only been able to measure RSSI (signal strength), and not the actual angle/directionality! I'm guessing I need some sort of directional transmission sent from the object, whether ultrasonic or RF, and correspondingly a 360-degree sensor array on the reference-station to determine direction.

Best Answer

If you're locating an object through auditory means, you'll need at least two receptive transducers - measure the difference in sound arrival time. Three are much better; you won't have to rotate the transducers for a second "ping" arrival.

If you're locating through radio means, you'll need a rotatable directional antenna... or three omnidirectional radio antennae. If one, you'll rotate it until signal strength is strongest. If three, you'll select the strongest and extrapolate direction from the relative strengths received by the other two.

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