Microwave and Optical Technology Letters最新文献

This paper proposes a 5G MIMO wideband four-coupled-feed square-ring patch antenna system specifically designed for access point applications in next-generation wireless communication networks. The system features a compact and low-profile form factor, with an overall footprint of 50 × 50 mm² and a height of 10 mm, making it well-suited for integration into space-constrained devices. The antenna array is built on a 35 × 35 mm² FR4 substrate with a thickness of 0.8 mm, corresponding to approximately 0.484 × 0.484 λ at the center frequency of 4.15 GHz. Each of the four antenna elements comprises a rectangular metal ring structure with dimensions of 19 × 13 mm² and is symmetrically arranged in a rotational configuration to ensure polarization orthogonality. This design approach effectively enhances port isolation, maintaining port isolation above 10 dB, without the need for additional decoupling structures. The antenna system operates efficiently across a wide frequency band from 3.3 GHz to 5.0 GHz, covering the sub-6 GHz spectrum allocated for 5G communication. Key MIMO performance indicators, including the envelope correlation coefficient (ECC) and channel capacity loss (CCL), are maintained below 0.09 and 0.2, respectively, across the entire band, signifying low mutual coupling.

This paper presents a novel ultra-wideband (UWB) miniature antenna operating from 0.25 to 14.9 GHz with VSWR < 2.5. Wideband coverage is achieved by integrating a compact dipole antenna with a series-fed log-periodic dipole array (LPDA). The dual-module design utilizes an equivalent tightly coupled dipole for low-band radiation and the LPDA for high-band operation. Replacing the terminal LPDA dipole with a compact dipole significantly enhances miniaturization. Measured and simulated results show a 59.6:1 impedance bandwidth, compact dimensions of 0.16λ₀ × 0.34λ₀ × 0.16λ₀, and gain of 3.22–8.57 dBi. This study successfully integrates a compact dipole within an LPDA, The proposed antenna is well-suited for applications such as ranging, side-looking radar, and microwave imaging.

This study proposes a highly sensitive metal-insulator-metal waveguide Nano-Refractive index sensor with triple Fano resonances for multi-parameter detection of plasma and ammonium chloride. Through coherent interference between discrete cavity modes and a broadband continuum, three distinct Fano resonances can be excited. The optimized sensor achieves a high refractive index sensitivity of up to 2219 nm/RIU. In practical testing, the sensor demonstrated a concentration sensitivity of 0.452 nm/(g/L) for ammonium chloride and 0.392 nm/(g/L) for plasma. This design supports simultaneous and time-shared detection of multiple analytes, offering a promising platform for real-time and efficient sensing in biomedical and industrial applications.

In the proposed article, a closely packed dual-band MIMO antenna with both linear and circular polarization is presented for 4G LTE, 5G NR n48/n78 communication systems. The modified E-shaped arm with a pair of vias is proposed with an edge-to-edge distance of 0.2 mm (0.0024 λo). This compact self-isolated polarized antenna gives linear and circular polarization at different frequency bands with high isolation and gain. Minimum isolation of 15 dB is achieved for both the operating bandwidth (2.6–3.55 GHz at ports 5–8 and 3.3–3.85 GHz at ports 1–4) with the peak gain of 4.6 dBi at 3.3 GHz and 4.4 dBi at 3.6 GHz, respectively. The proposed design stands out due to the antenna′s surface current cancellation property with no extra design for decoupling, thereby reducing the complexities along with high compactness. To verify the design, diversity parameters such as efficiency, radiation pattern, in-hand performance, and SAR (specific absorption rate) are calculated. The fabricated prototype shows good agreement with the simulated one, concluding that the proposed design is a good candidate for 5G mobile communication.

Accurate monitoring of atmospheric pressure and temperature is vital across multiple disciplines, including meteorological analysis and environmental assessment. This study presents a miniaturized fiber-optic sensing device that concurrently leverages Fabry-Pérot (FP) interference and anti-resonant (AR) guidance within a structure combining hollow-core fiber and photonic crystal fiber; the two optical mechanisms' distinct environmental sensitivities enable simultaneous pressure and temperature measurement, eliminating the need for multiple sensing units and contributing to a streamlined, cost-effective design, with experimental results showing that over the 0–0.9 MPa pressure range, the FP and anti-resonance spectral features respond with sensitivities of 3.897 nm/MPa and −3.268 nm/MPa respectively, while the AR spectrum envelope displays a temperature sensitivity of $��0.03��\; ���\; �\text{nm}���\; �{∕}^{\circ }�$C and the FP signal remains largely unaffected by thermal changes. Due to its compact architecture, straightforward fabrication process, and high measurement precision, the proposed sensor holds strong potential for real-world applications requiring dual-parameter environmental monitoring.

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.