Herein, a passive low-profile moisture sensor design based on radio frequency identification (RFID) technology is proposed. The sensor consists of an LC resonant loop, and the sensing mechanism is based on the fringing electric field generated by the capacitor in the circuit. A standard planar inductor and a two-layer interdigital capacitor (IDC) with a significantly higher fringing capacitance compared to that of a conventional parallel plate capacitor (PPC) are used, resulting in improved frequency offset and sensitivity of the sensor. Furthermore, a sensor tag was designed to operate at an 8.2 MHz electronic article surveillance (EAS) frequency range and the corresponding simulation results were experimentally verified. The IDC- and PPC-based capacitor designs were comprehensively compared. The proposed IDC sensor exhibits enhanced sensitivity of 10% in terms of frequency offset that is maintained over time, increased detection distance of 5%, and more than 20% increase in the quality factor compared to sensors based on PPC. The sensor’s performance as a urine detector was experimentally qualified. Additionally, it was shown experimentally that the proposed sensor shows a faster response to moisture. Both simulation and experimental data are presented and elucidated herein.
Dual-band branch-line couplers with arbitrary power-split ratios are presented. The use of crossed lines at the center of the dual-band coupler enables it to independently provide different power-split ratios to the two bands. Additionally, open stubs are utilized to enhance the stopband responses. The complete design procedure with example design curves is provided. For experimental verification, three dual-band couplers with power-split ratio combinations of +3 dB (S21:S31=2:1) and −3 dB (S21:S31=1:2), −3 dB and +3 dB, and 0 dB (S21:S31=1:1) and +13 dB (S21:S31=20:1) at 1 GHz and 2.5 GHz were designed and fabricated. The measured results are in excellent agreement with the ideal and full-wave simulated results. The measured difference of −13.3 dB between the power-split ratios of the two bands is the largest reported for a dual-band branch-line coupler.
In this study, a high-performance, dual linearly polarized patch array antenna is presented for satellite synthetic aperture radar (SAR) applications. The antenna features an aperture-fed stacked patch as the radiation element and a stripline feeding network. A high-performance and low-loss dielectric substrate RF-35 by Taconic, and a honeycomb substrate is used. The honeycomb substrate is used to maximize the impedance bandwidth and decrease the insertion loss of the antenna. The proposed antenna offers exceptional isolation between the antenna's ports in excess of 55 dB owing to its stripline feeding network. The via stitching technique is utilized to suppress the parallel-plate mode excited by the discontinuities in the stripline. The antenna is designed to possess a wide impedance bandwidth. A prototype antenna of size 2×4 elements, which operates in the X-band, is fabricated. Its impedance and radiation performance are experimentally verified, and the results are presented. The antenna exhibits a 15.7 dB peak gain and more than 40 dB of cross-polarization discrimination. In addition, a wide bandwidth of 19.4 % at a −10 dB return loss (RL) level is obtained.
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