# US 2014/0197928 A1 · System for and method of locating radio frequency identification (rfid) tags associated with items in a controlled area

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- Number: US 2014/0197928 A1
- Document ID: US20140197928A1
- Status: Published application
- Kind: A1
- Application number: 13/742,768
- Filed: 2013-01-16
- Published: 2014-07-17
- Earliest claimed: 2013-01-16
- Assignees: Symbol Technologies, Inc.
- Applicants: Symbol Technologies, Inc.
- Inventors: ALEXANDER M. JACQUES; BENJAMIN J. BEKRITSKY; MICHAEL J. KOCH
- Web page: https://patentgrep.com/patent/US20140197928A1

## CPC

- G06K 19/0723: {the record carrier comprising an arrangement for non-contact communication, e.g. wireless communication circuits on transponder cards, non-contact smart cards or RFIDs}
- G01S 3/28: using amplitude comparison of signals derived simultaneously from receiving antennas or antenna systems having differently-oriented directivity characteristics
- G01S 13/751: {wherein the responder or reflector radiates a coded signal}
- G01S 3/32: derived from different combinations of signals from separate antennas, e.g. comparing sum with difference
- G01S 3/74: Multi-channel systems specially adapted for direction-finding, i.e. having a single antenna system capable of giving simultaneous indications of the directions of different signals (systems in which the directions of different signals are determined sequentially and displayed simultaneously G01S3/04, G01S3/14)
- G01S 13/762: {with special measures concerning the radiation pattern, e.g. S.L.S. (aerials or aerial systems providing at least two radiation patterns, e.g. providing sum and difference patterns, H01Q25/00)}
- G01S 2013/0245: {Radar with phased array antenna}
- G06K: GRAPHICAL DATA READING (image or video recognition or understanding G06V); PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
- G01S: RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES

## Abstract

A radio frequency identification (RFID) tag reading system having a phased antenna array accurately locates RFID tags in a controlled area, by steering an interrogating beam over the controlled area to interrogate the tags and generate return modulated RF signals. A primary receiver steers a primary receive beam at a primary steering angle that is fixed during each tag interrogation. A primary demodulator demodulates and reconstructs the received return modulated signals. A secondary receiver, independently of the primary receiver, steers a secondary receive beam at a plurality of secondary steering angles. A secondary correlator/demodulator demodulates the combined return modulated signals, and utilizes the reconstructed signal reconstructed by the primary demodulator at each of the secondary steering angles. Both the primary and the secondary receivers cooperate to accurately locate the same tag.

## Claims

### Claim 1

A radio frequency (RF) identification (RFID) tag reading system for accurately locating RFID tags associated with items in a controlled area, comprising:
a phased antenna array;
an RF transmitter for steering an interrogating beam over the controlled area to interrogate the tags and generate return modulated RF signals from the tags by transmitting an RF interrogating signal over the phased antenna array to generate the interrogating beam;
a primary RF receiver for steering a primary receive beam over the controlled area at a primary steering angle that is fixed during each tag interrogation, and for detecting the tags by receiving and combining the return modulated RF signals as the primary receive beam over the phased antenna array, the primary RF receiver including a primary demodulator for demodulating the combined return modulated RF signals from the primary RF receiver to detect each tag, for reconstructing the received return modulated RF signal for each tag, and for measuring a primary received signal strength for each tag; and
a secondary RF receiver operative, independently of the primary RF receiver, for steering a secondary receive beam over the controlled area at a plurality of secondary steering angles by receiving and combining the return modulated RF signals as the secondary receive beam over the phased antenna array, the secondary RF receiver including a secondary correlator/demodulator for demodulating the combined return modulated RF signals from the secondary RF receiver, and for measuring a secondary received signal strength utilizing the reconstructed tag signal reconstructed by the primary demodulator at each of the secondary steering angles, whereby both the primary and the secondary RF receivers cooperate to accurately locate the same tag even if the secondary received signal strength is below a threshold value.

### Claim 2 (depends on 1)

The system of claim 1, wherein the RF transmitter includes a transmit beam steering unit operative for baseband steering the interrogating beam, and wherein the primary receiver includes a primary beam steering unit operative for baseband steering the primary receive beam, and wherein the secondary receiver includes a secondary beam steering unit operative for baseband steering the secondary receive beam; and further comprising a plurality of transmit/receive modules operatively connected between the phased antenna array and the RF transmitter and the primary and the secondary RF receivers, for converting the baseband steering to passband steering.

### Claim 3 (depends on 2)

The system of claim 2, wherein each beam steering unit includes a plurality of complex multipliers, and a plurality of programmable devices that set a complex coefficient for each complex multiplier to effect steering.

### Claim 4 (depends on 3)

The system of claim 3, wherein the beam steering unit of the primary RF receiver includes a primary complex adder coupled to the complex multipliers of the primary RF receiver to generate a combined primary output modulated RF signal for input to the primary demodulator, and wherein the beam steering unit of the secondary RF receiver includes a secondary complex adder coupled to the complex multipliers of the secondary RF receiver to generate a combined secondary output modulated RF signal for input to the secondary correlator/demodulator.

### Claim 5 (depends on 1)

The system of claim 1, wherein the primary demodulator is operative for reconstructing the received return modulated RF signal, for measuring the received signal strength for each tag, and for measuring at least one receive parameter that includes at least one of a backscatter link frequency and a reception time.

### Claim 6 (depends on 1)

The system of claim 1, wherein the secondary RF receiver is operative for changing among the secondary steering angles during a tag interrogation.

### Claim 7 (depends on 1)

The system of claim 1, and further comprising another secondary RF receiver identical to the first-mentioned secondary RF receiver, and wherein the primary RF receiver and both secondary RF receivers cooperate to accurately locate the same tag.

### Claim 8 (depends on 1)

The system of claim 1, wherein the secondary RF receiver is operative for steering the secondary receive beam by null steering.

### Claim 9 (depends on 1)

The system of claim 1, and a microprocessor for controlling operation of the RF transmitter, the primary RF receiver, and the secondary RF receiver.

### Claim 10

A radio frequency (RF) identification (RFID) tag reading method of accurately locating RFID tags associated with items in a controlled area, comprising:
steering an interrogating beam over the controlled area to interrogate the tags and generate return modulated RF signals from the tags;
steering a primary receive beam over the controlled area at a primary steering angle that is fixed during each tag interrogation;
transmitting an RF interrogating signal with an RF transmitter over a phased antenna array to generate the interrogating beam;
detecting the tags with a primary RF receiver by receiving and combining the return modulated RF signals as the primary receive beam over the phased antenna array;
demodulating the combined return modulated RF signals from the primary RF receiver to detect each tag, reconstructing the received return modulated RF signal for each tag, and measuring a primary received signal strength for each tag;
operating a secondary RF receiver, independently of the primary RF receiver, to steer a secondary receive beam over the controlled area at a plurality of secondary steering angles, and to receive and combine the return modulated RF signals as the secondary receive beam over the phased antenna array; and
demodulating the combined return modulated RF signals from the secondary RF receiver, and measuring a secondary received signal strength utilizing the reconstructed tag signal at each of the secondary steering angles, whereby both the primary and the secondary RF receivers cooperate to accurately locate the same tag even if the secondary received signal strength is below a threshold value.

### Claim 11 (depends on 10)

The method of claim 10, wherein the interrogating beam, the primary receive beam and the secondary receive beam are steered by baseband steering; and further comprising converting the baseband steering to passband steering.

### Claim 12 (depends on 10)

The method of claim 10, wherein the baseband steering is performed by setting complex coefficients.

### Claim 13 (depends on 10)

The method of claim 10, and measuring the received signal strength for each tag, and measuring at least one receive parameter that includes at least one of a backscatter link frequency and a reception time.

### Claim 14 (depends on 10)

The method of claim 10, and changing the secondary steering angles during a tag interrogation.

### Claim 15 (depends on 10)

The method of claim 10, and providing another secondary RF receiver identical to the first-mentioned secondary RF receiver, and wherein the primary RF receiver and both secondary RF receivers cooperate to accurately locate the same tag.

### Claim 16 (depends on 10)

The method of claim 10, wherein the steering of the secondary receive beam is performed by null steering.

### Claim 17 (depends on 10)

The method of claim 10, and controlling operation of the RF transmitter, the primary RF receiver, and the secondary RF receiver with a microprocessor.