Patent ID: 7714773
Filing Date: 2010-05-11
Classification: G01S

Abstract:
1. An RFID tag distance measuring system comprising: an RFID tag; a reader configured to output a predetermined carrier signal to an RFID tag and receive a reflected signal of the carrier signal from the RFID tag, wherein the system estimates the distance between the RFID tag and the reader, the reader comprising: wherein the scan control section controls the reception of reflected waves from the RFID tag of the signals at the multiple different frequencies, which are transmitted through the scan antenna, the scan control section switches from one scan pattern to another scan pattern if the reader does not receive signals from the RFID tag at a first frequency of the multiple different frequencies to the RFID tag, and the scan antenna control section switches from one scan pattern to another scan pattern if the reader does not receive signals from the RFID tag at a first frequency of the multiple different frequencies by using one scan pattern and retransmits signals at a third frequency of the multiple different frequencies to the RFID tag.