For the success of a large deployment of UHF RFID, easy-to-use and low-cost engineering tools to facilitate the performance evaluation are demanded particularly in installations and for trouble shooting. The measurement of interrogation area is one of the most typical industrial demands to establish the stable readability of UHF RFID. Exhaustive repetition of tag position change with a read operation and a usage of expensive measurement equipment or special interrogators are common practices to measure the interrogation area. In this paper, a practical method to measure the interrogation area of a UHF RFID by using a battery assisted passive tag (BAP) is presented. After introducing the fundamental design and performances of the BAP that we have developed, we introduce the measurement method. In the method, the target tag in the target installation is continuously traversed either manually or automatically while it is subjected to a repetitive read of a commercial interrogator. During the target tag traversal, the interrogator's commands are continuously monitored by a BAP. With an extensive analysis on interrogator commands, the BAP can differentiate between its own read timings and those of the target tag. The read timings of the target tag collected by the BAP are recorded synchronously with the target tag position, yielding a map of the interrogation area. The present method does not entail a. measurement burden. It is also independent of the choice of interrogator and tag. The method is demonstrated in a practical UHF RFID installation to show that the method can measure a 40 mm resolution interrogation area measurement just by traversing the target tag at a slow walking speed, 300 mm/sec.
