Diplexer-Based Fully Passive Harmonic Transponder for Sub-6-GHz 5G-Compatible IoT Applications

• Published in: IEEE transactions on microwave theory and techniques Vol. 67; no. 5; pp. 1675 - 1687
• Main Authors: Gu, Xiaoqiang, Srinaga, Nikhil N., Guo, Lei, Hemour, Simon, Wu, Ke
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.05.2019; The Institute of Electrical and Electronics Engineers, Inc. (IEEE); Institute of Electrical and Electronics Engineers
• Subjects: 5G applications; 5G mobile communication; Antenna design; Antennas; Architecture; Bandwidths; Circuits; Circular polarization; Conversion; Criteria; Diodes; diplexer; Diplexers; Engineering Sciences; Frequency conversion; frequency doubler; Harmonic analysis; harmonic radar; harmonic tag; harmonic transponder; Internet of Things; Junctions; Mathematical models; Radar; Resonant frequencies; RFID; Schottky diodes; Slot antennas; target detection; Transponders; 5G mobile communication; Radar; Harmonic analysis; Frequency conversion; Transponders; Junctions; Antennas
• ISSN: 0018-9480; 1557-9670
• DOI: 10.1109/TMTT.2018.2883979

A novel diplexer-based fully passive transponder is presented in this paper, which targets sub-6-GHz 5G-compatible internet-of-things applications. To alleviate the antenna design restrictions of traditional transponder with two separate antennas, a new architecture has been proposed with the introduction of a diplexer, which allows transponder to simply employ a dual-band antenna. In this paper, a dual-band circularly polarized omnidirectional spiral slot antenna, with enhanced bandwidth and gain performance, is designed as the transponder Tx/Rx antenna. Besides the new architecture, a diode selection criterion is proposed as well. Analytical models are derived, showing relationships between the diode's SPICE parameters and the conversion efficiency or conversion loss (CL) of such diode-based transponders. With help of the analysis, transponder designers can easily identify diodes to implement transponders with better performance. Under the guidance of the criterion, low-barrier diode SMS7630 is chosen for verification. Measured CL results of the transponder circuitry part show a noticeable improvement over the state-of-the-art works. The complete prototype was tested with radar's transmitting power of 25 dBm, and it presents a maximum read-out distance up to 7 m when the operating fundamental frequency is 3.5 GHz.