Design, Analysis, and Performance Evaluation of a UHF RFID Forward-Link Repeater

The range of UHF-RFID systems, involving passive tags, is typically limited by the tag's RF harvesting circuitry. In this paper a forward-link UHF RFID repeater is proposed. The repeater amplifies the reader-to-tag carrier signal. Then, a passive RFID tag can be successfully identified from a much larger distance, compared to current technology, by exploiting the sensitivity of the reader. The proposed repeater consists of low-cost components; namely a pair of antennas, a low-noise amplifier and passive electronics. The proposed design also accounts for out-of-band emissions and the limitations posed by the maximum effective isotropic radiated power of the EPC UHF Gen2 standard. In contrast to prior-art, it can be deployed with any commercial RFID reader. Link-budget analysis reveals i) that the location of the repeater is of great importance to the system, ii) the range depends on the reverse link and not on the forward, as in typical RFID technology and iii) optimum performance can be achieved with bistatic RFID readers and RFID tags, capable of harvesting RF power at higher input power-levels. It is shown that with common, commercial, monostatic RFID technology, a maximum range of 80m can be achieved. By deploying bistatic configurations, which allow for improved reader's sensitivity, the read-range could be extended to 350m. By “tuning” the tag's front-end to achieve good matching for increased incident power levels, the expected range could be increased to 2km. Experimental results validate the performance of the proposed repeater and reveal how the link budget is affected by the tag's front-end. 73m measured range is experimentally achieved with commercial monostatic RFID equipment.