Microwave and Optical Technology Letters最新文献

This study presents a combined theoretical and experimental exploration of a hybrid fiber-bulk master oscillator power amplifier (MOPA) laser operating in burst mode at a 10 kHz pulse repetition rate. By implementing an optimized pumping scheme, Gaussian-like gain profiles were achieved, ensuring uniform spatial beam characteristics throughout the MOPA amplification process. Full-energy beam quality assessment along orthogonal axes yielded measured values of M_x² = 2.8 and M_y² = 3.3, confirming favorable beam spatial characteristics. Additionally, temporal modulation of the burst envelope stabilized the pulse train output. The system demonstrated significant energy scaling, with the amplified pulse energy increasing from an initial 37.82 mJ to a maximum of 72.13 mJ, following a clear dependence on input pulse durations ranging in 20 ~ 80 ns.

In this study, we fabricated a U-band orthomode transducer (OMT) designed to measure the total radiated power (TRP) of an emission source and evaluated its performance through experiments and simulations. The proposed OMT achieved low loss and high isolation through a coupling slot and septum-based matching stub structure. To solve the problems of complicated fabrication and high cost that affect conventional multi-segmented OMTs, the proposed design adopts a simpler structure that allows easy and low-cost monolithic fabrication. In addition, we investigated the mechanical structure and manufacturability of the transducer using a cross-simulation analysis between CST and HFSS. The fabricated OMT was combined with a choke-ring antenna to detect electric fields in an OTA (over-the-air) test. The measured reflection loss, radiation pattern, and gain of the OMT and the antenna module indicated satisfactory performance in measuring TRP.

A gain-enhanced ±45° dual-polarized base-station antenna is proposed in this paper. Replacing a pair of basic-mode dipoles with nonuniform compressed fifth-order mode dipoles improves the gain. Cross-polarization discrimination (XPD) can be improved by bending the coplanar stripline (CPS), further enhanced by the reflector and sidewall design. A prototype is fabricated to verify the principle experimentally. The measurement shows that the antenna worked in 3.44–3.55 GHz(|S₁₁ | < −14 dB), with port isolation greater than 23 dB. The gains of ±45° polarization are 11.8 ± 0.4 and 12 ± 0.5 dBi, respectively, and the HPBWs are 67.5° ± 1.5°and 67.5° ± 2.5°, respectively. XPD can reach 20 dB at the boresight direction and more than 13.7 dB within ±60°, which meets the requirements of technical standards.

A novel unbalanced-to-balanced diplexer with high isolation and wide stopband characteristics is proposed. It uses a dual-mode resonator as the common resonator, coupled with uniform impedance resonators and step impedance resonators at different center frequencies to form the lower and higher bands of the diplexer. Transmission zero introduced by the dual-mode resonator effectively improves frequency selectivity, thus improving isolation. At the same time, a wide stopband is achieved by separating the spurious harmonics of the three resonators from each other. To verify the feasibility, a diplexer with center frequencies of 1.58 GHz and 2.46 GHz was fabricated, with in-band differential-mode isolation of 50 dB and 48 dB, respectively. Better than 20 dB stopband rejection up to 17 GHz.

This letter develops a self-decoupling method for closely spaced wideband endfire antenna arrays based on the modifications of the directors and the metallic ground. Two side-by-side placed elliptical shaped directors and ground plane etched with rectangular slots were employed in the design of self-decoupled antenna element. A two-element array was constructed with center-to-center element spacing of 0.5 λ_L. The operational bandwidth of the developed array covers the range of 4.65–5.15 GHz with the in-band port isolation level higher than 25 dB. To validate the extensibility of the developed self-decoupling methodology, a 1 × 4 linear array was constructed with the same center-to-center element spacing. The simulated results demonstrated port isolation level higher than 25 dB between all ports. The two-element and four-element reference and developed arrays were fabricated and measured, the measured results validated excellent consistency between the simulated and measured results.

A generalized plane wave spectrum (GPWS) method is proposed. The purposes are to extend the PWS to the half space with PEC boundary not only a free space, and to provide a technology for improving the reconstruction quality at the wedge structure in THz-CT. This study research a thick PEC half-plane surrounded by vacuum as a case. The principle of GPWS is to express the electromagnetic field in each layer structure by the corresponding continuous-spectrum, and obtain a singular integral equation system according to boundary conditions. To reduce the considerable computational effort for solving the singular integral equation system, one method is the singularity extraction based on geometric optic (GO-SE). However, in GPWS, GO-SE applied to multilayers will suffer the problems of difficult mathematical operation and wrong physical meaning. Therefore, to overcome these problems, we propose a singularity extraction based on inheritance propagation method (IPM-SE). Finally, the proposed method is well validated by comparing the numerical results with commercial EM software.

Quartz tuning forks (QTFs) play a critical role in quartz-enhanced photoacoustic spectroscopy (QEPAS). Theoretical analysis and simulation of QTF dimensions are essential for guiding sensor design, as they directly influence QEPAS signal performance. This study performed a comprehensive theoretical and experimental investigation of the effects of QTF geometry on key physical parameters, including resonance frequency and optimal laser incidence position. Simulation results were highly consistent with laboratory experiments, validating the reliability of the analysis method. The findings provide a valuable reference for the design and optimization of QTFs in QEPAS applications.

This paper presents an L-band dual-frequency pulse suppression navigation antenna for UAVs in complex electromagnetic environments. It utilizes a double-layer FR4 substrate sized $��100�\; �\times �\; �100��\; �{��\; �\text{mm}�}^2�$ with a 5 mm air dielectric layer in between. A single-feed probe simultaneously feeds the layers at 1.176 and 1.575 GHz. Circular polarization is achieved by eliminating the corners of the rectangular patches on both layers and L-shaped truncation on the lower layer. A cross-shaped slot and four “irregular” triangles are etched on both layers for antenna miniaturization. Finally, NXP BAP51-02 PIN diodes connect rectangular strips to the patches. The PIN diode is in reverse bias during navigation, and the antenna operates at 1.176 and 1.575 GHz. When high-power electromagnetic energy occurs, the PIN diodes undergo reversible breakdown and shift the antenna's center frequency to 1.019 and 1.416 GHz, causing interference to fall within the stop bands to suppress signal reception. The measurements are consistent with the simulation, demonstrating that the dual-frequency L-band antenna meets the navigation requirements for UAVs with pulse suppression functions in the presence of interference.

This letter proposed a high-gain and high-directivity bow-tie antenna array (BTAA) with a composite reflector (CR) and a gradient refractive index (GRIN) lens. The CR is composed of two types of units with different mechanisms while the GRIN lens consists of eight metamaterial units with different refractive index. The measured results show that the maximum gain of the target antenna is 13.22 dBi, antenna gain is improved about 4.75 and 1.15 dB based on these structures, respectively. In addition, the minimum value of half-power beamwidth (HPBW) in xOz plane is 37.1 degrees, the maximum value of the sidelobe level is -10.19 dB, the proposed antenna has a good directivity in operation band. The simulation and measurement results demonstrate that proposed antenna has a good application potential in shallow GPR systems.

Microwave-photonics technology enables advanced radar systems by leveraging high bandwidth and low-loss signal processing for enhanced target detection and tracking. This paper presents the design and implementation of an X-band photonics-assisted continuous wave radar system, specifically developed for the detection and parameter estimation of small unmanned aerial vehicles (sUAVs) using micro-Doppler time-frequency analysis. The system incorporates a novel image-based processing algorithm that extracts critical rotor characteristics, such as rotational speed, blade length, and tip velocity. A detailed link-budget and hardware configuration, including intermediate frequency signal parameters, low-noise amplifier range, and analog-to-digital converter specifications, are presented to support system performance evaluation. Extensive open-field experiments were conducted on multiple real-time targets—including two-blade, three-blade, and flapping-wing sUAV models—with varying tilt angles and ranges up to 75 m. The system demonstrated the ability to detect up to four simultaneous targets, with a measurement accuracy ranging from 91.8% to 99%. This study contributes a scalable radar architecture and robust detection framework for security-critical applications, such as drone surveillance, reconnaissance detection, and autonomous threat tracking.