Microwave and Optical Technology Letters最新文献

A chalcogenide (ChG) multi-slot waveguide gas sensor with ChG as the core layer and silicon dioxide (SiO₂) as the under-cladding layer is proposed. Multi-slot waveguide can be used in the mid-infrared gas measurement. The optimized power confinement factor (PCF) of the ChG multi-slot waveguide can be up to 41.3%, which is ∼20% higher than that of the optimized single-slot waveguide. At the absorption line located at 3.291 μm for methane (CH₄) measurement, the limits of detection (LoD) of single-slot, double-slot, triple-slot, quadruple-slot waveguide sensors are determined to be 68.9, 57.4, 52, 48.6 parts per million (ppm), respectively. Compared with other waveguide sensors in the mid-infrared, the PCF of the proposed multi-slot ChG/SiO₂ waveguide sensor is enhanced by five times, which has the potential for highly sensitive gas sensing.

This letter details the design and implementation of a millimeter-wave (mm-Wave) low noise amplifier (LNA) employing 150-nm gallium nitride on silicon carbide (GaN-on-SiC) high electron mobility transistor technology, specifically tailored for fifth-generation (5G) applications. The proposed GaN-based LNA integrates a hybrid matching topology alongside a co-design strategy, thereby optimizing the noise figure (NF) by minimizing interstage matching components. The fabricated LNA, spanning a total chip area of 2.3 × 1.4 mm², exhibits a linear gain in the range of 17.41–19.2 dB and maintains an NF within 2.32–3.06 dB. Additionally, commendable input/output return losses exceeding 7.5 dB are achieved across the 23–27.5 GHz, with the apparatus consuming approximately 150 mW.

In this brief, a synthesis design method is proposed for one-port absorptive bandpass filters (BPFs) with general Chebyshev response and transmission zeros. The method is based on coupling matrix theory, enabling the derivation of normalized coupling matrix coefficients based on user-defined parameters, including 3 dB bandwidth, in-band reflection coefficient, and out-of-band rejection. Moreover, it offers design equations for designing absorptive filters using transmission lines, coupling lines, and stubs, all with a length of one-quarter wavelength at the center frequency of the passband. To illustrate this method, a fourth-order absorptive BPF with a general Chebyshev response and two transmission zeros is designed, fabricated, and measured. The experimental results verify the effectiveness of the design method.

A design for manufacturing (DFM) of a well-performing wideband coaxial filter line using direct metal laser sintering (DMLS) additive manufacturing is proposed. The demonstrated transmission line is an air-filled coaxial line chosen for low loss and consistent group delay over the bandwidth. Transmission line theory is used first to account for the impact of the shorted stub needed to support the central conductor. Deviations due to parasitics are described to transition the design from an ideal model to a physical prototype. The constraints inherent in DMLS are discussed and accounted for throughout the DFM. This process is demonstrated with a prototype having return and insertion losses of greater than 10 dB and less than 1.64 dB, respectively, over a 5.3:1 bandwidth from 6.4 to 33.9 GHz with a flat group delay of 129 ps ± 7%.

To improve the image quality of terahertz (THz) continuous wave (CW) computed tomography (CT) under sparse-view projections, a sparse-view adaptive-weighted Bregman Huber total variation (AW-BHTV) method is proposed and experimentally evaluated at 0.11 THz. The Huber function is served as the fidelity term and TV function is worked for the regularization term, optimized by the adaptive weights, incorporating with iterative algorithms containing the modified simultaneous algebraic reconstruction technique (MSART) and the iterative filtered back-projection (FBP). Sparse-view reconstruction experiments are carefully implemented via polystyrene (PS) foam samples: Sample 1 and Sample 2, respectively. Under 20 projection angles by MSART based AW-BHTV, the values of rooted mean-square-error (RMSE), peak signal-to-noise ratio (PSNR), structure similarity (SSIM) and feature similarity (FSIM) are 0.0061, 22.1427, 0.8738 and 0.9902 for Sample 1 together with 0.0051, 22.9101, 0.8376 and 0.9885 for Sample 2 separately. All of the results above suggest that the proposed AW-BHTV method can effectively protect image details and strengthen image quality in sparse-view THz CW CT.

A dual-polarization linear phased array with a simple decoupling structure is designed for wide scanning in this letter. The suggested antenna is made up of two printed dipole antennas that are orthogonally arranged and have a high cross-polarized isolation. Metal sheets cladding on antenna substrates serve as a decoupling structure, with an array element spacing of 0.48 $��\; ��\lambda ��$. A linear phased array of seven elements is fabricated and measured to ensure that the planned array is feasible. The simulated and measured results demonstrate that the phased array can scan its main beam up to ±75° in dual-polarized excitations at 5.6–6.4 GHz. The co-polarized mutual coupling is below −28 dB, and the active reflection coefficient of the element is less than −15 dB.

A novel and compact two-pole quarter mode substrate integrated waveguide (QMSIW) based bandpass filter with ultra-wide stopband characteristics (rejection level > 20 dB, up to 4.05f₀, where f₀ is the center frequency of the bandpass filter) is designed and developed in this paper. The designed second-order filter comprises of two circular QMSIW cavity resonators. The filter is designed using the dominant TM₀₁₀ mode of the circular SIW cavity. The TM₀₁₀ modes of cavities are coupled through the arc-shaped slot etched in the middle layer. To verify the present design methodology, a second-order bandpass filter is fabricated and its characteristics are measured. The designed bandpass filter shows outstanding performance in terms of good fractional bandwidth of 14.45%, lower insertion loss of 2 dB and wider stopband behavior (rejection better than 20 dB up to 4.05f₀) in a given footprint. The experimental results of the filter matches well the EM-simulated ones.

This study introduces a new approach to achieve flexible impedance matching in a self-diplexing conventional patch antenna by using paired vias for impedance bandwidth tunability. The antenna design incorporates a rectangular radiating patch, an orthogonal arrangement of a couple of paired vias, and a bottom ground plane. The patch is excited with the help of two orthogonal microstrip feeds aligned along the centerline of the broadside and narrow sides of the patch. The orthogonal vias set enables dynamic impedance matching in two frequency bands, lower and upper ranging from 2 to 3 GHz. Optimized via placement achieves high decoupling between input ports, facilitating the self-diplexing phenomenon. To validate the proposed concept, a prototype with patch dimensions of $��\; ��49�\; �\times �\; �40�\; �\times �\; �1.57��\; �{\text{mm}}^3��$ has been analyzed, fabricated, and subjected to comprehensive experimental study. The experimental results demonstrate the successful realization of two distinct operating frequency bands, centered around 2.47 and 2.66 GHz, each exhibiting peak gain values of 5.75 and 6.31 dBi, respectively. The input port isolation values are noteworthy, measuring at −34B and −29.5 dB for lower and upper operating frequency bands, respectively. The design offers a low-profile, minimally coupled structure with independent band control and the unique ability to simultaneously transmit and receive signals.