Microwave and Optical Technology Letters最新文献

This letter presents an innovative design of a miniaturized ultra-wideband circularly polarized (CP) antenna based on a Vivaldi structure. The design employs four identical Vivaldi antenna elements arranged in a spatially rotated configuration on a dielectric substrate to achieve broadband circular polarization characteristics. A feeding network system incorporating three-stage second-order Wilkinson power dividers is specifically designed for phase control, delivering equal amplitude and a precise phase progression of 0°, 90°, 180°, and 270° across the 1.5–5.5 GHz frequency range. Prototype testing confirms an ultra-compact geometry of 0.21 λ_l × 0.21 λ_l × 0.19 λ_l (λ_l is the free space wavelength at 1.6 GHz), while demonstrating a 114.3% impedance bandwidth (IBW) and a 98.4% axial ratio bandwidth (ARBW). Measured results reveal stable radiation patterns and a peak circular polarization gain of 8.1 dBic. Combining broadband performance with spatial efficiency, this design proves particularly suitable for modern wireless communication scenarios with stringent requirements on antenna dimensions and frequency bands, such as satellite communications (SatCom) and 6G millimeter-wave systems.

This paper presents a low insertion loss frequency reconfigurable magnetless nonreciprocal filter based on time-modulated microstrip resonators. To achieve nonreciprocity, modulation signals are applied to the varactors through the microstrip circuits connected to each resonator. The center frequency of the proposed filter can be continuously tuned by changing the DC bias voltage applied to the varactors. We designed, simulated, and experimentally validated a fourth-order microstrip nonreciprocal bandpass filter at L-band. The results confirm that the center frequency of the proposed nonreciprocal filter can be tuned from 1.37 to 1.78 GHz (1.3:1 tuning) with a forward insertion loss from 2.1 to 2.6 dB and a backward isolation from 25 to 32 dB.

In this paper, a novel dual-band conformal fractal antenna is designed for wireless capsule endoscopy systems. The antenna achieves operational bandwidths of 14.9% and 23.9% at 1.4 and 2.45 GHz, respectively. It exhibits reliable impedance matching and directional radiation patterns with maximum gains of −10.5 dBi at 1.4 GHz and −17.4 dBi at 2.45 GHz, ensuring efficient communication within the complex in-body environment. The proposed antenna leverages the Hilbert fractal geometry to achieve both miniaturization and dual-band performance. it is validated through simulations in different human tissue models to study the effect of each tissue as the antenna travels through the GI tract, and it is then experimentally tested using pork meat to mimic the human muscle. The results are in a good agreement with a broad bandwidth of approximately 24.5% (from 1.25 to 1.6 GHz) and 26.08% (from 2.1 to 2.73 GHz), with maximum gains of −11.24 dB at 1.4 GHz and −20 dB at 2.45 GHz and adherence to the SAR safety requirements.

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.