Microwave and Optical Technology Letters最新文献

This paper discusses different methods to improve the radiation efficiency of plasma antennas in the Reconfigurable Central Plasma Antenna Array (RCPAA). The simulation is carried out in CST Microwave Studio, which shows that optimising the orientation and size of the gap introduced between the ground plane and surface wave coupler (SWC), representing a novel application of the defected ground plane (DGP) technique to plasma antennas, improves the gain and radiation efficiency. This paper proposes a modified equivalent circuit model incorporating additional lumped elements ($�\; ��\; ��\; �C_g���$ and $�\; ��\; ��\; �L_g���$) to analyse the coupling effect on the plasma antenna. The RCPAA achieves an $�\; ��\; ��\; �S_{11}���$ of −32.72 dB at 850 MHz with a improved gain of 3.3 dB and impedance bandwidth of 500 MHz. The gap also contributes to more than a 10% increase in the radiation efficiency of plasma antennas at resonant frequency, with a maximum efficiency of 25%.

Accurate and reliable detection of low-concentration carbon dioxide (CO₂) is crucial for environmental monitoring, industrial process control, and medical diagnostics. A highly sensitive CO₂ detection system has been developed based on the gas filter correlation nondispersive infrared (GFC-NDIR) technology, which is a cost-effective technological variation of NDIR. The system exploits the strong absorption characteristic of CO₂ molecules at 4.26 μm in the mid-infrared spectral region. The sensitivity and selectivity of the developed sensor system were significantly enhanced through optimized narrow-band optical filtering and the use of a low-cost broadband light source. A high-precision gas filter correlation wheel serves as a reference channel, effectively suppressing interference from source fluctuations, optical component drift, and cross-sensitivity from other environmental gases. The system achieves a minimum detection limit (MDL) of 3 ppb for CO₂ under ambient temperature and pressure conditions, with a response time of less than 30 s and long-term stability of better than ±2% of full scale per 24 h. The developed system holds broad application prospects in areas including environmental greenhouse gas flux monitoring, enclosed space safety warning, and high-purity gas quality control.

This paper presents a waveguide-to-chip transition for monolithic microwave integrated circuit packaging, targeting millimeter-wave and subterahertz applications. The proposed structure employs a flip E-plane probe that interfaces directly with gold bumps, eliminating bondwires to minimize parasitic inductance and signal path length while reducing radiative leakage. An integrated air window cavity accommodates the chip and acts as a power dissipation shield, suppressing higher-order modes to enhance broadband performance. Measurement results demonstrate that the transition achieves an average insertion loss of 0.73 dB and a return loss better than 10 dB across the D-band (110–170 GHz), offering a compact and efficient solution for high-frequency system integration.

The field generated by a time-harmonic pure irrotational current distributed in a finite region of free space is derived analytically. Only an electric field is produced and is nonzero even merely within the finite interior of the current distribution, though the problem space itself is infinite. To consider the obtained field solution nonphysical according to our current physical concepts, however, lacks evidence or reasoning. It satisfies the original first-order Maxwell's equations (MEs) and the related continuity conditions exactly, hence cannot be rejected mathematically. It is also shown that a conceptual denial of such a different kind of solution based on physical interpretations of other known solutions of the same MEs is logically not acceptable. A direct experiment study is necessary to conclude convincingly whether or not the above solution is physical. The completeness problem of MEs and their consistency with the Lorentz force law and the equation of motion are discussed. Free space MEs are incomplete or underdetermined due to the absence of a curl equation for the current density. If the solution is nonphysical, ME-based electromagnetic (EM) theory is not self-consistent. On the other hand, if it is physical, this type of inconsistency within the frame of the ME-based EM theory disappears, yet it is inconsistent with the Lorentz force law and the equation of motion in this case.

This paper introduces an innovative four-channel filtering power divider with cross-coupling, leading to the design of two Substrate integrated waveguide (SIW) filtering antenna arrays. A 2 × 2 antenna array with varying phases and multiple radiation zeros is developed, achieving a compact size and effective stopband suppression, thereby enhancing signal transmission and radiation characteristics. Experimental results reveal a S₁₁ ≤ −10 dB and a peak gain of 9.5 dBi within the 12–13 GHz passband, alongside the generation of five radiation zeros outside the passband. And next, the paper elaborates on the principle of harmonic suppression and its equivalent spur line structure model, incorporating these into the filtering divider. By extending the microstrip feeder and utilizing stacking technology, a 4 × 4 antenna array with a wide stopband and multiple zeros is realized, significantly improving radiation effects. Final test results indicate an in-band peak gain of 14.1 dBi, out-of-band selectivity of 114.65 dBi/GHz and 67.8 dBi/GHz, and an S₁₁ ≤ −15 dB. The stopband extends to 1.85 f₀ with an attenuation exceeding 16.1 dBi, with the radiation direction aligning closely with simulation results. These features position the antenna as a formidable candidate in field of satellite communications.

In current beamforming multi-objective optimization algorithms, parameter adjustment to satisfy the target pattern given the target pattern is essential. In order to avoid the influence of experience factors on the optimization target weight parameters, we proposed for the first time an intelligent optimization method that combines the optimization algorithm with the RL algorithm to assist in adjust the weight parameters. For different antenna array models, this method can also achieve excellent array beamforming. This article compares the results of PSO with auxiliary adjustment and the results of classic PSO without auxiliary adjustment on three array models and three groups of beam targets, proving the versatility and effectiveness of the algorithm for auxiliary adjustment of intelligent optimization algorithms.

This work investigates flat-band slow-light performance in photonic crystal waveguides featuring ring-shaped holes. Using Finite Element Method based numerical optimization, we show that precise tuning of the inner radii and spatial arrangement of the first two rows of holes strongly governs the dispersion profile. For the first time, a combined optimization strategy employing independent tuning of both ring dimensions and bi-directional positional shifts in the first two rows is demonstrated to enhance slow-light performance in RPCWs. The optimized designs achieve ultra-low dispersion across 16–31 nm bandwidths, with group indices of 11.2–14.85. A best-performing structure delivers a normalized delay–bandwidth product of 0.264 and group velocity dispersion ≈10⁵ps²/km, representing a clear improvement over previously reported ring-hole PCW designs. These results demonstrate a robust pathway for engineering high-performance slow-light waveguides suitable for compact delay lines and enhanced nonlinear photonic devices.

In this paper, a balanced nonreciprocal linear-phase bandpass filter (BPF) based on time-modulated resonators is reported for the first time. A linear-phase response is achieved by integrating group delay equalization circuits adjacent to both the balanced input and output ports of a balanced nonreciprocal BPF, implemented on a microstrip circuit. Compared to conventional passive BPFs, the balanced nonreciprocal BPFs based on time-modulated resonators exhibits different group delay characteristics. This work introduces an innovative group delay equalization circuit, specifically designed for nonreciprocal BPFs based on time-modulated resonators. By utilizing resonators with different resonant frequencies under common-mode and differential-mode excitation, the balanced circuit provides effective common-mode suppression, which enhances immunity to electromagnetic interference and crosstalk compared to single-ended circuits. A microstrip prototype was fabricated for the proof-of-concept demonstration, and the measurements show good agreement with simulations.

In this paper, we proposed a quartz-enhanced photoacoustic spectroscopy (QEPAS) sensor system for detecting dissolved carbon monoxide (CO) in transformer oil. The sensor system was designed to be highly sensitive, compact, and cost-effective. An on-beam configured acoustic micro-resonator (AmR) coupled with a quartz tuning fork functions as an acoustic transducer to enhance photoacoustic signals. This sensor system achieved a minimum detection limit (MDL) of 0.37 ppm for CO based on the absorption line with a wavelength of 2333.72 nm. This value is three orders of magnitude lower than the safety threshold specified in relevant standards for dissolved gas detection in transformer oil. The proposed method offered high sensitivity, low cost, a compact form factor, and ease of integration, offering a novel technical solution for dissolved gas detection in transformer oil.

The Born approximation (BA) and Rytov approximation (RA) are common in solving electromagnetic inverse scattering problems (ISPs). However, purely applying these approximations only yields rough inversion results. To this end, a noniterative combined modified method using the real part (CMM-R) is presented to extend the limitation in accuracy and effectiveness encountered by traditional Born/Rytov-based approaches. Based on the connection between modified RA (MRA) and modified BA (MBA), the complementary strengths of MRA and MBA are integrated. Specifically, these two modified inversion methods are implemented by employing the dominant current, whereas only the real part of MRA is used to mitigate phase wrapping issues. The simulation and experimental results demonstrate that the proposed CMM-R achieves higher accuracy than traditional modified Born/Rytov-based methods for imaging mild scatterers. As a noniterative method, CMM-R provides a robust initial guess for further iterative algorithms.