Microwave and Optical Technology Letters最新文献

This paper proposes a Harris Hawks Optimization (HHO)-based approach for rapid small-signal modeling of GaN high electron mobility transistors. It pioneers the application of HHO to efficiently construct 19-element equivalent circuit models over the 0.1–40 GHz broadband. To address challenges including strong parasitic/intrinsic parameter coupling in high-dimensional space, broadband accuracy imbalance of conventional fitness functions, and parameter magnitude disparities, key innovations are introduced: sequential optimization of grouped parameters for decoupling, physical constraints for integrated circuits, parameter normalization, and a frequency-weighted fitness function. Experimental results demonstrate that the proposed method achieves 34.4% CPU time reduction with 16.1% higher accuracy in parasitic parameter extraction compared with conventional optimization methods, while outperforming genetic algorithm and particle swarm optimization algorithm in intrinsic parameter optimization with faster convergence, lower error, and no requirement for manual parameter tuning. Close agreement between measured and modeled S-parameters across 0.1–40 GHz validates the methodology's effectiveness.

A compact, high-selectivity third-order multichannel bandpass filter is proposed in this letter based on creased microstrip resonators (CMRs), which employs the complementary coupling technique using stubs. A six-channel filtering response with equal bandwidths that operate at the same frequency has been demonstrated. To achieve transmission zeroes on both sides of the passband, stepped-impedance open stubs as the coupling mechanism are used, resulting in high frequency selectivity in the passbands. The transmission zero positions are adjustable by a change in the coupling gap between the stubs and the resonators, and a combination of its electrical parameters. The circuit has been optimized and fabricated for measurement, at a 3.5 GHz center frequency. An overall size of 0.39 λg × 0.39 λg is achieved. The results exhibited high selectivity with two transmission zeroes located at 3.25 and 3.75 GHz, isolation levels below 21 dB, insertion loss lower than 1 dB and return loss higher than 20 dB in all passbands. A stopband range of 0.75 GHz each is achieved on both sides, and the rejection level is below 25 dB in both stopbands. The measured responses conform to the simulated responses.

This paper presents a dual-slot Vivaldi antenna incorporating elliptical slots and metamaterial structures, featuring ultra-wideband (UWB) operation and high gain. The proposed antenna achieves bandwidth extension through corner-cutting techniques and optimization of the T-junction power divider and radiating patch dimensions. To enhance gain performance, five pairs of tapering inclined elliptical slots are strategically etched on the edge of the radiating patch, while metamaterial structures are integrated into the antenna aperture. The synergistic integration of these structures effectively tailors the surface current distribution and electric field patterns, enhancing the antenna's aperture radiation efficiency. This yields a maximum gain enhancement of approximately 2.3 dB without altering the antenna's physical dimensions. The antenna exhibits a compact profile of 130 mm × 86 mm × 0.787 mm, with an ultra-wide operating band of 1.3–12.0 GHz. It consistently attains gain exceeding 10dBi across most operation frequencies, and even in the frequency range of 5.5–12.0 GHz, its gain exceeds 12.0 dBi. Notably, both the E-plane and H-plane radiation patterns exhibit extremely narrow half-power beamwidths (HPBW) and high directivity. The average HPBW of the E-plane is 31.7°, with a minimum of 16.2° at 12 GHz, while that of the H-plane is 60.4°, with a minimum of 30.9° at 12 GHz. These attributes make the proposed antenna highly suitable for advanced microwave imaging systems.

In this letter, a broadband high-power eight-way coaxial waveguide power divider is proposed. The structure consists of one large coaxial tapered waveguide and eight branched coaxial tapered waveguides. A coaxial stepped impedance matching structure is introduced to suppress reflection peaks and broaden the operating bandwidth, while rectangular slots are incorporated near the inner conductor plane to redistribute the electric field and thereby enhance the power capacity. A prototype is designed, fabricated, and experimentally tested. The results show that the proposed power divider operates from 4.8 to 14.95 GHz with a power capacity exceeding 100 kW. Within the 100.8% relative bandwidth, the measured input return loss is better than—10 dB, and the maximum efficiency reaches 99.44%.

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.