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Identifying and locating low cost RFID transponders

"A new identification technology"

"Better than a tape measure!"

RFID-radar represents a major technical development in the technology of Radio Frequency Identification (RFID).
RFID-radar now adds location information to the identity information that was provided by previous RFID equipment.

The Problem - How can you measure range using low cost transponders

RFID systems comprise a tag and a reader. As operating range increases, the number of tags in the reader zone is likely to increase and multiple tags need to be read at the same time.

Before the arrival of RFID-radar, readers have been able to read the identity of multiple transponders in a zone at one time, but they have not been able to locate where in the zone the transponders actually are physically.

As the performance of readers and transponders improve, operating ranges increase giving one reader the ability to monitor larger areas meaning location information in addition to the identity information becomes very important.

RFID-radar works with very low cost transponders and relatively cheap reader systems.

Rfid radar kit with Patch antennas
Trolley Scan's new RFID-radar kit with High gain patch antennas

The invention

  • Trolley Scan have developed a reader system capable of fixing the location of many passive transponders in a reading zone
  • The invention can monitor a zone up to 100 meters deep, to an accuracy of less than 0.5 meters.
  • The scan time to range all tags in the zone is a couple of seconds.
  • Once located individual transponders can be tracked.
  • The transponders are low cost Tag-Talks-First type devices, capable of being produced at a few US cents.
  • The reader has only one array of antennas
  • The reader is relatively low cost to produce.
  • The reader is able to map out the location of all the transponders in the field in 1D, 2D or 3D space, processing all the transponders in its reading zone in parallel.
  • The reader uses only 10kHz of bandwidth, operating at UHF frequencies, allowing many readers to operate in close proximity with minimal interference.
  • The reader provides a range measurement to each tag as well as a pointing vector with an accuracy better than 1 degree.
  • Position updates are given at 1 second intervals
  • The system can be implimented in all countries of the world
  • This is a world first base technology, allowing companies involved in its development the ability to deliver very advanced low cost RFID systems for many years.

    Physical location of transponders

    Placement of twelve transponders in front of a radar for a test showing capabilities

    Potential applications

    The following are some potential applications of RFID-Radar technology. To date this technology has been very expensive meaning that only military type applications could afford to use it in the past.
    Locating parcels and bins of goods in 3D space. Tracking the progress of goods automatically from goods receiving to storage. Radar can be fitted even to a fork lift truck so that it can image and locate objects in the immediate vicinity of the apparatus.
    Where is my tank? - Where is my platoon? - Where is my patrol hiding in the long grass? - Where did I leave the landmine?
    Monitoring security patrols
    Using the track feature of the RFID-Radar to monitor that guards do perform their patrols correctly. Monitoring can be done via computer monitor program covering large area.
    Asset movement
    Real time tracking of assets in a building/office, tracking both the laptops, computers, etc and the people if needed.
    Monitoring the location, attendance and safe passage of pupils in the classroom and on the public transport - from when they leave home in the morning to returning in the evening
    Monitoring the traffic of delegates past the sponsors' booths at conferences
    Tracking individual animals in a herd, and also detecting if any of the herd stray beyond fences (theft)
    Tracking trolleys in a parking lot at an airport or supermarket to monitor if any trolley is being removed from the premises
    Old Age homes
    Watching residents of an old age home to detect if any stray beyond the boundaries of the property.
    Nursery school
    Watching children in a playground to check that none stray near dangerous equipment or leave the premises
    Shopping centres
    Monitoring for lost or seperated children in a crowded shopping centre - Where is my child?
    Parking lots
    Providing a monitoring service to report where your car is parked in a public garage.
    Museums and galleries
    Monitoring many artworks from a single location to ensure they are not moved
    Electricity Utility Transmission line integrity
    Monitoring the height of transmission lines above the ground to detect impending failure or breakage
    Dam wall integrity
    Monitoring the profile of a daw wall continuously to millimeter precision to detect impending failure
    Mine tunnel clearage
    Monitoring the dimensions of a mine tunnel to detect rock burst
    Monitoring the movement of patients, staff and equipment in a hospital environment to speed up locating the person/object in an emergency
    Reporting the location of parcels for distribution on a warehouse floor.
    Loyalty cards at retail stores and banking outlets
    Notifying management of the arrival of important clients.
    Finding missing luggage at airports. Tracking luggage and passengers through the airport to ensure all arrive at the aircraft on time.
    Monitoring commuters in Underground transit systems
    Tracking the progress of commuters electronically in conjunction with the CCTV systems in use at present
    Barcode replacement
    Trolley Scan have in the past been known for developing advanced retail systems for the checkout of goods from a supermarket - both through the Branders and the Waverider system. Their protocols allowed the same numbering system to be used as was in use with the existing EAN/UCC barcode numbering system. Now Trolley Scan have advanced the technology far beyond the restrictions of the barcode in that we can now report location information as well as all the features in the earlier RFID systems for retail.
    Golf ball
    Where are the golfers?.
    Technology advancement
    Will one still be able to find a market for an RFID reader system in the future that does not also give location?. Can you still market an XT computer after the arrival of the Pentium?

    Rfid-radar with transponder
    Trolley Scan's new RFID-radar front panel showing simple controls for 2D scanning


    Twelve transponders are plotted. The yellow zone is the field of view of the radar. The axes are in meters.

    The equipment

    The system comprises tags and readers.

    The reader

    The reader provides an energy field to power up the transponders, and measures the distance the signal travels from the transponder back to the reader. For 2D and 3D applications, two or three receiver channels are included in the reader to allow angle of arrival to be determined at the reader site by comparing the range from each of the reader channels.

    The reader contains a fast processor module making up to 10000 range measurements per second to allow the tracking of each of the tags in the zone with update rates at one second intervals.

    The reader interfaces to other computer networks via RS232.

    The reader has one array of adjacent antennas measuring range from that array to the tags. The array contains one transmit antenna for energising the passive transponders and one antenna for each receiver (2 antennas total for 1D,3 antennas for 2D and four for 3D).

    The reader can be set to operate in any frequency range from 860 to 960 Mhz, using 10 kHz of spectrum for the energising signal. Two reader systems can operate within 4 meters of each other. The reader processor consolidates the huge amount of information retrieved by the reader sections. It can report

    1. Identity of tags in the field.
    2. Identity, range and pointing vector to the tag in 1D, 2D or 3D space
    3. Identity and track of movement of tags in the reader zone, updated at 1 second intervals.
    The reader has a location accuracy of better than 0.5 meters, a pointing accuracy of 1 degree and will eventually cover a maximum range of 100 meters depending on the tag used with the reader.

    The tags

    Typical transponders in a credit card sized format and stick format

    These are passive backscatter Ecotag UHF transponders. They can be packaged in different antenna forms. Operating range depends on the sensitivity of the transponder, with the 5 uW versions operating up to 40 meters, and the 200uW versions working out to 10 meters.

    Operating range is a function of two processes

    • The ability of the computer algorithms in the radar to determine the range
    • The ability to power a tag at a distance and to detect the weak signal returning
    The radar algorthm has a practical operating range for measurement of 100 meters with better than 0,5 meter accuracy.
    The current 200uW Ecochiptags with the current energiser has a maximum operating range of 10 meters and the 5uW stick tags have a range of 40 meters.We currently have also developed other forms of transponders with a maximum range of fifty meters. As we develop more sensitive transponders so this range can increase.


    Accuracy range50 centimeter in absolute mode & millimeter resolution in relative mode
    Max no of dimensions3
    Pointing accuracy0.2 degree
    Maximum range of reader100 meters (mathematical) Energising dependant on transponder type- 40 meters for current 5uW tags
    Transponder technologyPassive TTF (Tag talks first) protocol
    Multiple transpondersUp to 50 in the energising zone
    Interfacing to computer network RS232
    Field of view 64 degrees- 80 degrees
    Operating frequency of reader860 to 960 MHz
    Operating bandwidth of reader10kHz
    Interference zone with second reader on close frequency4 meters
    Multipath discrepanciesRange corrected for multipath

    Competitive technologies

    Ranging beacons These are very sophisticated transponders that are attached to expensive military hardware in warehouses for locating where the "Military tank is parked". The transponders cost more than US$1000 each and the warehouse has to be fitted with ranging beacons all over the warehouse to provide triangulation.
    WiFi/Bluetooth GPS units fitted in each transponder with the position data communicated via WiFi networks. Transponders are very expensive and are major user of battery energy for the communication and position location.
    Fingerprinting/Multilateration The site where the transponders are to be used has to be mapped before use showing power fluctuations of signals on multiple receivers caused by a single source. Susceptible to other objects being moved into the site after survey impacting the survey, multipath variation due to reflections and needing multiple receivers. Very crude positioning technique.


    Any Ecochiptag,Ecowoodtag, laundrytag, Ecosportstag, Ecofarmtag or the new 5 microwatt long range tag can be used with the RFID-radar. The reader has two receiver channels to measure the range and one energising channel for powering the transponders. The reader uses a 10kilohertz bandwidth, allowing many readers to operate in close proximity.

    The radar measures the distance the signal travels from the various transponders to the radar antenna. By comparing the range on two receivers, the angle of arrival can be measured and so a direction and range can be shown. The reader can process about 50 transponders in a zone at a time, at the rate of 10000 range measurements per second, and can operate up to ranges of 100 meters with suitable transponders. Only one set of antennas is needed for a full fix with one reader. A third receiver channel can be added to give 3D coverage rather than 2D coverage. A major feature of the system, besides its accuracy in measuring the range, is that the interference generated by this radar for other similar users and for other RF users, such as cell phones, is very low.

    Another feature of the radar system is the ability to track moving targets. By measuring the range many times per second of each transponder, the reader can plot the path of a moving object in its field of view.

    The reader outputs location and identity information at regular intervals, which can be displayed on a laptop running a Visual Basic program to show a radar type display.

    The radar can also locate and process transponders attached to wood and metal.

    Importance of this invention

    "The RFID-radar has the performance of a US$1million battlefield radar, but at the price of an RFID reader"

    When read ranges of RFID systems are small, then location information is not important as it is always in close proximity to the reader. As technology improves and the transponders need less and less power to operate, so the read range starts increasing, meaning the uncertainty in the exact location of the transponder increases. This improved sensitivity transponder technology needs increased information from the reader to assist in the speedy location of the transponder and here the technology detailed in this brochure becomes important.

    This invention is the only solution to the RFID-Radar problem that uses low cost transponders.

    The arrival of RFID-radar has stimulated the development of lower powered UHF backscatter transponders to increase operating range. While conventional RFID readers typically would want maximum read ranges of about ten meters, RFID-radars ability to report location means that ranges of 40 meters from one reader are being requested.


    A reader that can generate position information of all tags in its aperture, and provide updates of their movement, generates a lot of data.

    Trolley Scan are one of the world leaders in UHF RFID developments and manufacture leading edge designs which they export currently to 44 countries.

    Trolley Scan are now delivering

    • Commercial models to companies wanting to evaluate the technology.
    • The commercial versions have a DSP processor onboard for performing the calculations, make 10000 measurements per second, and able to handle 50 targets in the zone at one time.
    • "OEM versions" for including in the clients hardware are now being delivered. Trolley Scan provide the RFID-radar module and the client handles the interfacing of the data to the operator.

    Specifications of commercial version now being supplied

    The specifications of the system are:
    • 2 D scanning
    • Dual receiver, single energiser with three high gain patch antennas
    • Supplied with 15 5uW transponders (operating range of 35 meters) and 5 200uW credit card sized transponders.
    • Uses single board computer with embedded software for computation
    • Interfaces to a user supplied computer for display of data communicating via RS232 link
    • Software (source and executable code) supplied for display computer allowing client to adjust display software to their requirements. The display software runs on any Windows based (Win32) operating system in DOS console mode.
    • Radar outputs position at one second interval for each transponder in the zone
      • Identity of transponder (within a few milliseconds of entering the field)
      • Range and angle of transponder(takes a few seconds for accurate readings as has to obtain a lock first)
      • Predicted path based on historical measurements for transponders that are moving and pass through null zones.
    • The radar in 2D format weights 12kg and is shipped in a 32 by 32 by 45 cm box
    • The operating frequency can be factory set to any frequency betwen 860-960Mhz with a 10kHz bandwidth.
    • Operating power adjustable by the operator between 0.5 and 3.5 watts.
    Trolley Scan will upgrade any supplied model to any later versions when available at a cost of the parts, a small service fee and provided the client takes care of freighting and duty costs in returning systems to South Africa for upgrade.

    How does RFID-radar work?

    The radar makes two measurements on each signal received from each transponder in its receiving zone - namely a range measurement and an angle of arrival. It is the ability to measure range with narrow bandwidth that make this an outstanding unique RFID instrument. The system uses the same transponders that are used by conventional RFID readers allowing RFID-radars and RFID readers to monitor the same transponder simultaneously.

    Light and radio waves travel at the speed of light, namely 300 000 000 meters per second. RFID systems need to operate in a crowded RF spectrum, where other RFID systems, cell phones, radio stations and other communication users have to share the available radio spectrum. RFID-radar uses just 10 kilohertz of bandwidth to operate, meaning it can detect time differences only as small as 0.1 milliseconds, or 0.0001 seconds. In this time the radio wave will travel 30 kilometers, or 30 000 meters or 3 000 000 centimeters Yet the radar is able to determine the range of the transponder based on its received transmission to an accuracy of a few centimeters, or nearly 1 million times better than its basic time measuring properties. If we used a conventional military radar approach and wanted to get centimeter precision, then we would have to measure the time of flight to 0.3pico seconds (.3*10-12) which would use 300GHz of radio spectrum.

    RFID-radar pay for this million times improvement in the timing accuracy of the basic system by taking a longer time to determine the exact position. As a result it is well suited to a static situations where transponders are relatively stationary. However developments are in progress to address the accurate tracking of movement by adapting some of the principles of operation.

    The angle of arrival measurement is virtually instantaneous and used in conjunction with range gives a 2D positioning system from a single measuring location.

    Frequently asked questions(FAQ)

    What is the big deal with this technology?
    To explain the problems associated with measuring range using RFID-radar technology one can consider a simile.

    Imagine you are sitting on a chair at the edge of a large lake on a pitch black night, overcast with no stars. There are no visual references to use for range estimation. A boat somewhere out on the lake flashes a torch briefly and the person on the chair has to calculate the range of the boat from the chair to an accuracy of 1 meter. There are no other people on chairs on the lake that can also give information, just you on your chair, possibly with one eye closed. This highlights the technical challenges we have overcome using this invention.

    Now imagine there are 50 boats out there scattered randomly, who all flash their lights briefly and are expecting their location to be identified.

    Now imagine all the boats start moving and you have to track their individual paths while sitting on your chair.

    How intensive is the computing problem for this invention?
    An RFID-radar system tracking 50 targets that are moving can generate a lot of information. The load is most probably similar to that of AWAC aircraft flying above a battlefield. Each target in the zone has to have its own set of complex equations to describe its movement in isolation from all the other targets.

    Despite this large amount of source information, the calculations are done in the reader and the reader can condense the information on each target to identity and coordinate details only so as not to overload the computer network.

    What are the practical problems with measuring the distance a signal has travelled from a reader to a transponder
    Radio waves travel at 300 000 km/sec. Due to there being many users of the radio spectrum trying to share a very limited spectrum, operating bandwidths for practical RFID systems are only tens of kiloHertz wide. This means measuring accuracies for time of travel of the order of 0.1 milliseconds(each tick of the clock). With this resolution for measuring the range of a tag by the time of travel of a signal results in an uncertainty in position measurement of 30 kilometers for each tick of the clock. RFID-radar has overcome this challenge and measures the range from a transponder to a reader.

    Does RFID-radar use triangulation to measure range?
    The RFID-radar has a single set of antennas mounted next to the radar processing box. From this single location, the radar measures the range to each target and computes the apparent arrival angles at this one antenna location. From this range and bearing information, the RFID-radar can determine the location of multiple targets in the zone. The RFID-radar does not use triangulation, which would require other remote antenna systems. Because of its single antenna set for reading location, RFID radar is suitable for mobile applications, like mounting on a fork lift truck, to identify goods in the vicinity of the fork lift truck.

    Does RFID-radar use signal strength variation to measure range?
    Signals travelling from a transponder to the reader would dissipate their energy in all directions radiating from the transponder, causing a variation of signal strength as one travels further from the transponder. However any signal hitting any hard object in any location around a transponder(even a floor or a wall), would also cause a radiation signal which would have similar characteristics and which would interfere with the original signal, either reducing or increasing its strength - commonly known as multipath. Multipath corrupts the characteristic of signal strength and reduces its ability to be an indicator of range, especially over long range. To overcome multipath and hear signals that are close, or far at the same time, RFID-radar can accept variations in signal strength of more than 100 000 times. RFID-radar does NOT use signal strength as an indicator of range.

    Will RFID-radar work with different brands of transponders?
    Initially RFID-radars are being produced to work with Trolleyponder, EcoTag and similar passive transponders.It will also work with certain active transponders to give greater operational range. Later other brands of transponders can be added to the lists of transponders that can be used with this new technology once the RFID-radar reader is adapted to read the other brands of transponders.

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    If you are looking for conventional RFID systems, operating at UHF frequencies and offering long range (13 meters), passive, fast (300kph), multiple transponders (up to 700 in a zone), credit card sized transponders, low radio interference, able to operate in all countries of the world (already used in 45 countries), fixed and portable readers - then look at Trolley Scan at http://trolleyscan.com/

    "RFID-radarTM", "ClaymoreTM" and "Better than a tape measure!TM" are the trademarks of Trolley Scan (Pty) Ltd

    RFID-radar is a development of Trolley Scan (Pty) Ltd (South Afica), one of the world's leading developers of UHF RFID technology.

    Trolley Scan (Pty) Ltd © / info@rfid-radar.com