Microwave and Optical Technology Letters最新文献

With the rapid deployment of fifth-generation (5 G) mobile communication technology, radio frequency (RF) front-end components require higher performance to suppress interference in the n1 frequency band (1920–2170 MHz) coexisting systems. This paper proposes a compact bandstop filter (BSF) based on complementary split-ring resonator (CSRR) integrated with defected ground structure (DGS), occupying dimensions of 0.58λg × 0.72λg. Experiments results demonstrate operation at 2.07 GHz center frequency with 24.2% fractional bandwidth (1.82–2.32 GHz), achieving > 23.6 dB stopband suppression and < 0.5 dB passband insertion loss. An equivalent circuit model based on transmission line theory exhibits close agreement with measurements, confirming the hybrid structure′s effectiveness in suppressing spurious responses. This design achieves a balance between compact dimensions and high stopband performance, offering an efficient solution for 5 G base stations.

This paper proposes a nonreciprocal pattern reconfigurable filtering antenna, which has nine different radiation states. The proposed structure is a double-sector Vivaldi antenna configuration, and each sector unit can generate a unidirectional radiation beam. A feeding network integrated with time-modulated resonators is used to excite the sector units. By dynamically controlling the phases of each resonator, various nonreciprocal radiation patterns can be achieved. A prototype antenna centering at 4 GHz is fabricated and measured, which realizes nonreciprocal reconfigurable radiation patterns. Moreover, the prototype exhibitsa bandwidth of 25% (3.6–4.6 GHz) and a filtering response with an in-band gain of 3.5 dB and an out-of-band rejectionof 13 dB.

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.