Microwave and Optical Technology Letters最新文献

A broadband omnidirectional filtering dipole antenna having controllable operating bandwidth and radiation nulls is proposed. A step-shaped dipole antenna, driven by a 50 Ω coaxial cable, generates a basic resonant mode for omnidirectional radiation. A parasitic U-shaped strip is loaded near the dipole to generate a second resonance and a lower-band radiation null, while a parasitic meander-shaped strip is etched around the dipole to create a third resonance and a higher-band radiation null. In this case, the proposed design realizes a broad passband bandwidth and excellent out-of-band filtering response. Additionally, both the operating bandwidth and radiation nulls can be effectively controlled by adjusting the filtenna parameters. The proposed antenna achieves a broad impedance bandwidth of 33.4% (0.685–0.960 GHz), a stable gain of 3.5 ± 0.7 dBi, and high selectivity with a stopband rejection level of 17.8 dB.

This article presents a vector-fitting (VF)-based fast Q-factor extraction method for multimode resonators. Firstly, by introducing a frequency mapping technique, the RLC resonators in the equivalent circuit model of the multimode resonator are simplified to the resonators resonant near the zero normalized frequency. This approximation enables the input admittance of the simplified circuit model to be modeled as an Nth-order (N is the number of modes) rational function in the normalized frequency domain. Then, the VF is employed to perform rational modeling of the input admittance, combined with a one-dimensional search algorithm to remove the additional time delay introduced by the embedded transmission line at the port. Finally, the equivalent circuit model is constructed by the poles and residues of the input admittance, and the Q-factors are thereby obtained. For validation, an ideal circuit of a quintuple-mode resonator and two circularly polarized dual-mode patch antennas is used. For the ideal circuit, the extracted Q-factors closely match the preset values. And for the dual-mode antennas, the reflection and the axial ratio predicted by the equivalent circuit model also show good agreement with the measured data.

This letter proposes a novel approach for designing a 3×3 Nolen matrix with integrated filter function. The proposed Nolen matrix is realized by utilizing the combination of two 90° couplers, a compensation filter, and a 180° filtering coupler, providing phase increments of −90°, 30°, and 150° at the output ports. For experimental validation, a prototype 3×3 filtering Nolen matrix was devised, fabricated, and measured. The prototype operates at a center frequency of 2.4 GHz and exhibits second-order bandpass filtering characteristics. The measured results show close agreement with the simulated ones, thereby confirming both the validity of the design method and the practical feasibility of the proposed structure.

A waveguide-to-microstrip Gysel power divider (WMGPD) has been presented in this study. The implementation of a Gysel network between the in-phase microstrip bifurcations is proposed as a method to enhance the isolation between the output ports of the divider. Passive experiments of the WMGPD have demonstrated that the isolation level exceeds 14 dB within the Ku-band spectrum. The active combination verified an output power of approximately 80 watts, exhibiting an efficiency rating that surpassed 95.5%. The experimental findings demonstrate that, in comparison with conventional 3-dB power dividers, the WMGPD exhibits enhanced isolation, elevated combining efficiency, and considerable power handling across a substantial frequency range.

This letter presents a low-cost, circularly polarized (CP), stacked patch antenna that exhibits a wider CP operating bandwidth compared to other low-cost antennas of the similar type. The proposed antenna consists of two FR4 dielectric substrates, a metallic plane, and two air layers. The radiator is composed of a metallic elliptical ring and a split corner-truncated patch, which operate at two axial ratio (AR) minimums. The performance of the AR is further enhanced by the metallic plane and a centrally symmetric defected ground structure (DGS). The dimensions of the antenna are 0.58λ₀ × 0.58λ₀ × 0.22λ₀, (where λ₀ is the free-space wavelength at the center frequency). To validate the design, the antenna was fabricated and measured. The relative impedance bandwidth (IBW) of |S11 | < −10 dB is 32.7% (2.81–3.91 GHz). The relative AR bandwidth (ARBW) of AR < 3 dB is 13.2% (3.31–3.78 GHz). The overlap of these bandwidths essentially covers the 5 G_N78 band. Additionally, the measured average gain within the operating bandwidth is 5.30 dBi, with a peak gain of 6.28 dBi. This antenna is low-cost and offers a CP operating bandwidth that meets the requirements of the 5 G_N78 band, while also maintaining competitive dimensions and gain. It is well-suited for deployment in 5G base stations.

A novel omnidirectional antenna that has both extra-low-profile and electrically small size is proposed for indoor base station applications. The antenna consists of a rectangular monopole radiator, a metal top cap with two slots, two shorting pins, and two types of materials that include the dielectric material with relatively high permittivity and the magneto dielectric. The reduced size and increased bandwidth are simultaneously achieved by loading the materials in their property-matched regions. The antenna achieves extremely small dimensions of 0.12λ₀ × 0.096λ₀ × 0.028λ₀, where λ₀ is the free-space wavelength at the lowest operation frequency. A measured impedance bandwidth for |S₁₁| < −6 dB ranging from 824 to 894 MHz is realized, which covers the GSM850 band. The peak realized gain is up to 1.2 dBi within the operating frequency.

Magnetic resonance imaging (MRI) is increasingly popular for noninvasive quality inspection of fruits and vegetables in the food supply chain (FSC). The signal-to-noise ratio (SNR) serves as a crucial performance metric in MRI, the enhancement of which can be exchanged for elevated image clarity or reduced acquisition time. In this paper, a cylindrical wireless metasurface-based coil (CWMC) is proposed to enhance the SNR of 1.5 T MRI system for fruits and vegetables. The self-detuning circuits (SCs) of CWMC causes it to be detuned in the transmitting stage (TS), and make it resonate at 63.8 MHz in the receiving stage (RS), which not only eliminates interference with the B₁ field but also significantly boosts the B₁^– field received by the volume coil (VC). According to the MRI results, the implementation of CWMC has boosted the SNR by 8.9 times as the VC works in the transmit-and-receive scenario, surpassing the SNR achieved with a 12-channel receiving coil (12ch-RC). Furthermore, the CWMC demonstrates compatibility with common MRI sequences, and induces low specific absorption rate (SAR) values. The proposed CWMC is wireless and convenient, which can make the quality inspection of fruits and vegetables more efficient in 1.5 T MRI system. And it demonstrates considerable potential on promoting the development of food quality assessment technologies.

RF and Microwaves-based sensors are gaining researchers' attention because of their non-invasive and non-ionizing nature for diabetes management, and affordable nature of this technology with no side effects. This article, therefore, proposes a flexible circular patch antenna with diamond wand shape, as a radiator for sensing changes in BGL in correspondence to S parameter variation. To improve the gain and front-to-back ratio of the proposed radiator, it is backed with a hexagonal-shaped metasurface. The proposed sensor (Antenna + Metasurface) is then simulated with a three-layered bio-phantom with varying BGL, and the S-parameter data is captured in 3D EM software, CST MWS EM simulator. The proposed sensor resonates at 2.45 GHz, covering the Industry Scientific Medical band of 2.4–2.5 GHz with a gain of 8.09 dBi and a specific absorption rate of 0.0008 W/Kg. The validation of the proposed sensor is done by fabricating (using a wet etching process) and testing the proposed antenna and AMC for their radiation properties using a VNA (Keysight E 5063) and an anechoic chamber. The BGL detection procedure is validated by preparing aqueous glucose solutions of different glucose concentrations (100, 200, 300 and 400 mg/dL) and comparing the measured and simulated S parameter values for these cases. Additionally, to accurately predict the blood glucose values using S₁₁, regression analysis of the S parameter data is carried out using Machine Learning algorithms such as Support Vector Regression, Random Forest, Extreme Gradient Boosting, and Optuna-tuned Cat Boost (OtCB) models. The OtCB model showed the best performance with a R² score of 0.9982 and a mean absolute error of 0.0742, and hence is best suited for predicting BGL values for the current usage. The models demonstrated a median absolute error below 0.3 dB even after synthetic noise injection, which shows their robustness for real-life practical scenarios.

A six-beam pattern-reconfigurable patch antenna for wearable Wireless Body Area Network (WBAN) applications is proposed. Based on the Yagi-Uda principle, the antenna features an innovative structure with a regular hexagonal driven patch as the core and six symmetrically distributed parasitic patches as switchable units, breaking through the structural limitations of traditional Yagi-Uda antennas and enabling a low-profile, lightweight, and integrable design. By using PIN diodes to control the parasitic patches′ function switching between reflectors and directors, combined with the combinatorial coding control of the six units, precise beam steering in six discrete directions in the azimuthal plane is achieved. Compared with existing Yagi-Uda-based reconfigurable antennas, it offers more beams with simpler switching logic and no need for complex feeding networks. A physical prototype was fabricated and measured, with the measured results showing good agreement with simulations. The antenna demonstrates stable performance around 2.8 GHz, and its extremely low simulated specific absorption rate (SAR) values comply with international safety standards, confirming its viability and safety for wearable applications.