Methods and Systems for Estimating Distance of a Radio Frequency Identification Tag

A device for determining a distance of a radio frequency identification (RFID) tag, comprising:

• a reader configured to transmit a plurality of interrogation signals to the RFID tag at a plurality of frequencies, and receive therefrom a plurality of response signals in response to the plurality of interrogation signals;
• and
• a processor communicatively coupled to the reader and operative to:
• determine a phase of each of the received plurality of response signals, and a first distance estimate of the distance based on a signal strength measured from a first response signal of the plurality of response signals;
• based on the determined phases and the first distance estimate, calculate a phase slope;
• and
• determine a second distance estimate of the distance based upon the phase slope.

A non-transitory computer readable storage medium having stored thereon instructions that when executed by a machine result in the following operations:

• determining phases of a plurality of response signals at a plurality of frequencies received from a radio frequency identification (RFID) tag in response to interrogation signals by a reader at the plurality of frequencies;
• calculating a first distance estimate of a distance between the RFID tag and the reader based on a signal strength measured from a first response signal of the plurality of response signals;
• based on the phases and the first distance estimate, calculating a phase slope;
• and
• determining a second distance estimate of the distance based upon the phase slope.