Novel 10-dB Directional Coupler for Wireless RF Interrogator of SAW Resonator Sensors: Design, Simulation, and Experimental Investigation
Abstract
This manuscript presents a novel planar 10 dB microstrip directional coupler intended for use in a dedicated wireless RF interrogator operating in the UHF ISM band around 433 MHz. The wireless coupling of a SAW resonator to an RF interrogator is possible through the use of an antenna-based link, enabling remote excitation of the resonator by the interrogator and the detection of variations in its resonance frequency or phase as a function of the sensed physical parameter. The proposed design uses compact microstrip resonators based on open-circuited transmission lines to overcome the narrow trace width requirement associated with high impedance for 10 dB coupling and to reduce the large circuit size at UHF frequencies, enabling a more compact and practical PCB implementation. The coupler is first analyzed theoretically using the ABCD matrix method to meet the required electrical specifications. The optimized layout is then implemented on an FR-4 substrate and simulated using the 2.5D ADS Momentum solver, followed by full-wave validation with CST. The prototype is fabricated using an LPKF milling machine and experimentally characterized. Measurement results demonstrate good impedance matching with input reflection coefficients below -11.3 dB over the 380-460 MHz frequency range. At the 433 MHz center frequency, the coupler achieves a transmission coefficient of approximately -1.3 dB, a coupling level of -10 dB, and an isolation of -20 dB. The miniaturized design features series and shunt resonators with electrical lengths of 0.11 lambda_g and 0.12 lambda_g, respectively, while maintaining broadband performance without compromising electrical characteristics.
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BibTeX
@article{sardi2026novel,
title = {{Novel 10-dB Directional Coupler for Wireless RF Interrogator of SAW Resonator Sensors: Design, Simulation, and Experimental Investigation}},
author = {Azzeddine Sardi and Younes El Hachimi and Yassine Gmih and Ghizlane Boussatour and Amine Ennawaoui and Hicham Mastouri and Chouaib Ennawaoui and Mohamed Boutghatin and Othmane Marbouh},
journal = {IEEE Access},
year = {2026},
month = aug,
doi = {10.1109/access.2026.3723038},
url = {https://hal.science/hal-05718857v1},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Novel 10-dB Directional Coupler for Wireless RF Interrogator of SAW Resonator Sensors: Design, Simulation, and Experimental Investigation
AU - Azzeddine Sardi
AU - Younes El Hachimi
AU - Yassine Gmih
AU - Ghizlane Boussatour
AU - Amine Ennawaoui
AU - Hicham Mastouri
AU - Chouaib Ennawaoui
AU - Mohamed Boutghatin
AU - Othmane Marbouh
PY - 2026
DA - 2026/08/12
JO - IEEE Access
DO - 10.1109/access.2026.3723038
UR - https://hal.science/hal-05718857v1
AB - This manuscript presents a novel planar 10 dB microstrip directional coupler intended for use in a dedicated wireless RF interrogator operating in the UHF ISM band around 433 MHz. The wireless coupling of a SAW resonator to an RF interrogator is possible through the use of an antenna-based link, enabling remote excitation of the resonator by the interrogator and the detection of variations in its resonance frequency or phase as a function of the sensed physical parameter. The proposed design uses compact microstrip resonators based on open-circuited transmission lines to overcome the narrow trace width requirement associated with high impedance for 10 dB coupling and to reduce the large circuit size at UHF frequencies, enabling a more compact and practical PCB implementation. The coupler is first analyzed theoretically using the ABCD matrix method to meet the required electrical specifications. The optimized layout is then implemented on an FR-4 substrate and simulated using the 2.5D ADS Momentum solver, followed by full-wave validation with CST. The prototype is fabricated using an LPKF milling machine and experimentally characterized. Measurement results demonstrate good impedance matching with input reflection coefficients below -11.3 dB over the 380-460 MHz frequency range. At the 433 MHz center frequency, the coupler achieves a transmission coefficient of approximately -1.3 dB, a coupling level of -10 dB, and an isolation of -20 dB. The miniaturized design features series and shunt resonators with electrical lengths of 0.11 lambda_g and 0.12 lambda_g, respectively, while maintaining broadband performance without compromising electrical characteristics.
SN - 2169-3536
SN - 2169-3536
ER -