Microwave and Optical Technology Letters最新文献

This letter presents a low-profile, wideband, polarization-insensitive frequency selective rasorber (FSR) designed to reduce the radar cross section (RCS) of high-gain planar antenna arrays. The proposed structure consists of a lumped resistor-based lossy top layer and a lossless bottom layer, separated by an air gap. It achieves high absorptivity (> 90%) across 3.8–7.85 GHz and 9.67–13.4 GHz, while maintaining an in-band transmission at 8.5 GHz with an insertion loss of 0.9 dB. The fourfold symmetric and compact topology ensures polarization insensitivity and angular stability up to 50° incidence. The FSR is integrated with a planar microstrip patch antenna array, effectively reducing its out-of-band RCS under X-polarization and both in-band and out-of-band RCS under Y-polarization, without affecting in-band transmission. Both the standalone FSR and the integrated antenna system have been fabricated and measured, demonstrating up to 10 dB RCS reduction over a 111% fractional bandwidth under normal incidence.

In this paper, we present the design of a planar endfire circularly polarized (CP) antenna utilizing a periodic structure. The CP antenna is constructed on substrate integrated waveguide (SIW) that incorporates a periodic double-sided rectangular slot structure, culminating in a Vivaldi antenna at the end. The rectangular slot array generates vertically polarized (VP) electric field components for the far-field, while the Vivaldi antenna contributes horizontally polarized (HP) electric field components. By adjusting the distance between these two components, we achieve a phase difference of 90° between the two polarization components. This results in a planar endfire CP antenna that operates within the frequency range of 23.8 to 25.8 GHz, with an axial ratio of less than 3 dB. The antenna achieves a maximum gain of 11.73 dBi. The combination of high gain at small aperture translates to superior aperture utilization and easy edge/board integration, supporting compact endfire arrays, terminal-side AoA links and 24-GHz ISM sensing. Compared with recent planar endfire CP designs, the proposed radiator delivers comparable bandwidth but higher gain with smaller width, using a simple, low-loss, and manufacturing-friendly single-layer PCB implementation.

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.