DISTANCE MEASURING APPARATUS, DISTANCE MEASURING METHOD, REFLECTOR AND COMMUNICATION SYSTEM

摘要

A transmission control section (7B) controls to transmit a R/W request signal for requesting transmission of a tag response signal to a RFID tag (1) twice. At this time, a frequency control section (7A) controls a PLL section (5A) to transmit the R/W request signals at different transmission frequencies, respectively. A phase information acquiring section (8A) detects each phase change quantity of the tag response signals transmitted at the different transmission frequencies, and based on the phase change quantity, a distance calculating section (8B) calculates a distance between a reader writer (2) and the RFID tag (1).