1. Field of the Invention
This invention relates generally to position determination and tracking systems. More specifically, this invention relates to radio frequency identification (RFID) tag systems, methods and readers. Still more specifically, the present invention relates to RFID tags and tag readers that utilize a scanning antenna or an electronically steerable passive array antenna for significant system improvements.
2. Background Art
Many product-related and service-related industries entail the use and/or sale of large numbers of useful items. In such industries, it may be advantageous to have the ability to monitor the items that are located within a particular range. For example, within a particular store, it may be desirable to determine the presence and position of inventory items located on the shelf, and that are otherwise located in the store.
A device known as an RFID “tag” may be affixed to each item that is to be monitored. The presence of a tag, and therefore the presence of the item to which the tag is affixed, may be checked and monitored by devices known as “readers.” A reader may monitor the existence and location of the items having tags affixed thereto through one or more wired or wireless interrogations. Typically, each tag has a unique identification number that the reader uses to identify the particular tag and item.
Currently, available tags and readers have many disadvantages. For instance, currently available tags are relatively expensive. Because large numbers of items may need to be monitored, many tags may be required to track the items. Hence, the cost of each individual tag needs to be minimized. Furthermore, currently available tags consume large amounts of power. These inefficient power schemes also lead to reduced ranges over which readers may communicate with tags in a wireless fashion. Still further, currently available readers and tags use inefficient interrogation protocols. These inefficient protocols slow the rate at which a large number of tags may be interrogated.
As the antennas in readers are typically omni-directional or, at best, manually directed, positioning information can only be obtained if the tags can be sure of their position and can relay the information to the reader. However, if the tags are moved or are moving or do not possess their position information, their angular position cannot be determined. Thus, there is a strong need in the art for an RF ID tag system and method that can determine the angular position of the tag relative to the reader.
Further, because the antennas are omni-directional and are constrained by FCC power limitations and other power constraints as mentioned above, the range is very severely limited. Hence, there is a strong need in the industry to provide an antenna that can allow for scanning and directionality for significant signal gain and overcoming multipath problems. Since omni-directional antennas always read all tags at all times, this limits the number of tags a reader can handle. With a directional beam, you can have more total tags in the area since only the tags that are being illuminated by the beam will be read.
Thus, in summary, what is needed is a tag that is inexpensive, small, and has reduced power requirements, can provide tag directional information and that can operate across longer ranges, so that greater numbers of tags may be interrogated at faster rates and with position information.