Microwave and Optical Technology Letters最新文献

In this letter, a method of designing quasi-elliptic bandpass filter with ultrabroad reflectionless bandwidth and high selectivity is proposed. It is implemented on the basis of a quasi-elliptic absorptive lowpass filter (ALPF) prototype that features both a low-reflection response over all normalized frequencies and two controllable transmission zeros near the passband. A distributed-element absorptive bandpass filter (ABPF) scheme using coupled-line units is derived from this quasi-elliptic ALPF prototype. With this distributed-element ABPF scheme, both ultrabroad reflectionless bandwidth and compact size can be realized. Equations for closed-form design are derived. A microstrip ABPF operating at 2.0 GHz (i.e., f₀) is designed for validation. The measured roll-off rates of the upper and lower transition bands are 116.44 and 157.41 dBc/GHz, respectively. The return loss is better than 10 dB from direct current to 6.25f₀. The size of the overall circuit is 0.12λ_g².

In this paper, a design procedure of a compact broadband microstrip diplexer working on the Very High Frequency (VHF)/Ultrahigh Frequency (UHF) band is proposed. The diplexer consists of a fourth-order Butterworth Low-Pass Filter (LPF) and a sixth-order elliptic High-Pass Filter (HPF). The two filters are located on two substrates with a common ground. A microstrip-to-coaxial structure is utilized to transmit the power flow between the two substrates. For miniaturization, the utilized ideal capacitors and inductors are realized by the commercial lumped-element capacitors and the curved microstrip line sections, respectively. All the middle design and rapid optimization processes from the schematic simulation by Advanced Design System (ADS) to the circuit simulation by CST STUDIO SUITE (CST) are given in the article. A prototype is fabricated and measured. The testing results are consistent with the simulation. The diplexer can operate at 225–775 and 880–2500 MHz. The insertion losses are 0.8 ± 0.3 and 0.9 ± 0.4 dB in the two working bandwidths. The isolation bandwidth of −20 dB level is as small as 105 MHz. The roll-off is also sharp that the related bandwidths corresponding to the attenuation level −3 to −20d B are 90 and 30 MHz to the high and low bands, respectively. Besides, the return loss and isolation are larger than 10 and 20 dB approximately. The diplexer has a volume of 0.065 λ_g × 0.156 λ_g @775 MHz, which can be utilized to feed the miniaturized broadband VHF/UHF antenna system.

In this paper, a quasi-lumped element-based bandpass filter is implemented by substrate-integrated suspended line (SISL) technology. To miniaturize the filter size, a deep hole drilling capacitor (DHDC) structure is proposed. The properties of DHDC are derived by parametric analysis and equivalent circuit analysis. Based on derived properties, a quasi-lumped element bandpass filter using SISL technology is designed and fabricated. Experimental results demonstrate that the proposed bandpass filter achieves the center frequency $��\; ��f_0��$ of 1.48 GHz, with a fractional bandwidth of 50%. The minimum insertion loss within the passband is 0.96 dB, while the return loss exceeds 23.14 dB. The maximum out-of-band suppression is over −50 dB, and the filter size is only 0.172 λ_g× 0.062 λ_g.

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.