Readout Distance Enhancement of Battery-Free Harmonic Transponder

摘要

This work proposes to enlarge the maximum readout distance of battery-free harmonic transponders through a careful Schottky diode selection and a consideration of lowtemperature operations. Diode SMS7621 is identified to deliver lower conversion loss (CL) of harmonic transponders based on a diode selection guide. Moreover, an analytical method for studying temperature effects on the transponder CL performance is introduced and derived with satisfactory accuracy. A diplexer inserted in the harmonic transponder design can help reduce the antenna number. To mitigate matching difficulties at both fundamental and second-harmonic frequencies, a third-order diplexer is developed to enhance its bandwidth performance. Experimental verification has shown that low-temperature operations can effectively reduce the CL of the SMS7630-based harmonic transponder, thus increasing its readout distance. Specifically, its maximum readout distance at -40 degrees C has increased by more than 10%, from 6.4 to 7.1 m, compared with that at +40 degrees C. A complete harmonic transponder based on SMS7621, with dimensions of 85 mm x 45 mm has reached a maximum readout distance of 8 m when the fundamental frequency is 3.5 GHz.