An X-band vehicle-location system

A vehicle-location system operating at X band is described. For certain applications, a precise absolute measure of position is not needed. It suffices to determine a vehicle's location only to within a zone. For those systems which require zonal location information only, an "electronic fence" approach is well suited. In this approach, zone boundaries are defined by an array of transmitters. These transmitters, of low power and limited range, continuously emit digitally coded messages (identifying the zone) which are received and stored in the vehicle's receiver. When the vehicle's location is desired, a separate radio data channel is used for interrogation, whereupon the vehicle responds with the last stored message corresponding to the zone presently occupied. The transmitter and receiver portions of the locator were implemented using microwave components and both analog and digital integrated circuits. Although the unit has been designed and tested for a zonal fence configuration, it can easily be used as a basic sensor element in any other vehicle-locator system of the proximity type.