Li Xu

This paper presents a current-reused vertically stacked (CRVS) topology for a high-dynamic-range amplifier (HDRA) implemented in a 0.1 μm GaAs pHEMT process, targeting wideband millimeter-wave (mm-wave) receiver front-ends. The proposed design breaks the inherent trade-off between noise figure (NF), linearity, and bandwidth, achieving simultaneous enhancement of transconductance efficiency, Miller effect suppression, and wideband matching. The fabricated prototype operates over a continuous 20–43 GHz bandwidth (covering K- and Ka-bands), demonstrating state-of-the-art performance: a flat gain of 24 ± 0.6 dB, a minimum NF of 2.2 dB, a maximum output 1 dB compression point (OP1dB) of 15.8 dBm and a low power consumption of 5 V/65 mA, with both input and output return losses better than −10 dB across the entire band. The results validate the effectiveness of the CRVS topology and highlight the competitiveness of GaAs pHEMT technology for high-performance wideband mm-wave front-ends, making the design suitable for applications including 5G/6G communication, satellite systems, and mm-wave test equipment.

Families of slowly changing nonsingular large sparse linear systems arise frequently in many simulation problems in science and engineering. We consider iterative solution with recycling techniques for a general case where both left-hand sides and right-hand sides of the systems change from one family to the next. We firstly develop a generalized product-type method in the framework of recycling biconjugate gradient method (RBiCG), referred to as RGPBiCG, which can also be considered as a recycling variant of GPBiCG. However, as the same situation in RBiCG stabilized method (RBiCGSTAB), the construction of recycling spaces in RGPBiCG requires expensive computational costs due to invoking other algorithms (like RBiCG) to compute approximate eigenspaces. In order to further reduce such computational costs, we alternatively form the recycling spaces in RGPBiCG with difference vectors of approximate solutions, as employed for loose GMRES (LGMRES), resulting in a more promising algorithm termed as LR-GPBiCG. Numerical experiments on both a set of academic problems and engineering simulation problems demonstrate the efficiency of our proposed algorithms.

The inherent properties of electromagnetic metamaterials, such as their large-scale, periodic, multi-media, and complex geometric structures, make the Finite Element Method with the Domain Decomposition Method (FEM–DDM) an ideal simulation approach. Coupling FEM–DDM with the boundary element method (BEM) can further improve solution accuracy. In this work, an efficient non-conformal FEM–BEM–DDM method for electromagnetic scattering analysis of metamaterials is developed. This method employs FEM–DDM for internal finite-periodic metamaterial modeling, coupled with BEM for open-domain electromagnetic analysis. Moreover, a series of computational techniques have been developed for metamaterial electromagnetic analysis. To minimize computational complexity, non-matching mesh and matrix reuse is implemented at the subdomain interfaces, effectively reducing the solution’s degrees of freedom. An efficient three-level preconditioner and the MLFMA are introduced to optimize the efficiency of iterative solution. The proposed method provides an efficient and accurate framework for electromagnetic scattering analysis of metamaterials.

In this letter, an efficient radiation analysis method for large scale finite periodic array antenna is proposed. This method is based on finite element domain decomposition and leverages the periodicity of array antenna elements to achieve memory reduction through sub-domain matrix reuse. Meanwhile, a matrix preconditioner tailored for finite element domain decomposition is further employed, and an equivalent boundary method is adopted to simplify the computational complexity of multilayer thin-sheet dielectric structures. Subsequently, a far-field equivalence computation method is employed, which directly derives the far-field distribution of large-scale arrays by solving small-scale array problems, thereby significantly lowering the complexity of radiation analysis in large-scale antenna arrays. This method enables computationally efficient radiation analysis of large-scale arrays, even with thousands of elements, significantly reducing processing time and resource demands.

To solve the linear systems with multiple right-hand sides (RHS) arising from the implicit hybridizable discontinuous Galerkin time-domain (HDGTD) method for electromagnetic simulations, we propose a block version of generalized minimal residual method with deflated restarting technique (BGMRES-DR). To accelerate convergence, two improvements are introduced. The first is a better strategy that is designed to select initial values to restart a new round of iterations. The second one is that a multifrontal block incomplete Cholesky (MFBIC) factorization is employed as the preconditioner. Numerical results demonstrate its efficiency in computing multiple RHS problems

Based on our previous research on the explicit–implicit hybridizable discontinuous Galerkin time-domain (ex–imHDGTD) method, this letter gives two important applications in time-domain multiscale electromagnetics. The first is that the different ratios of both coarse and refined meshes are discussed, which shows that grid division strategy has a significant effect on the performance of ex–imHDGTD. The second is that a total-field/scattered-field (TF/SF) method is derived to impose the excitation on interfaces instead of boundary faces. Compared with the traditional hybridizable discontinuous Galerkin (HDG) method, the introduction of TF/SF changes the formulations of both local and global linear systems. Once applying this TF/SF in ex–imHDGTD, it is very easy for 3-D waveguide problems to obtain the transmitted and reflected waves. Note that this is the first time the TF/SF is used in the ex–imHDGTD method. Numerical results show that the proposed applications are feasible due to higher computational performances.

This article presents a study on the utilization of annular beams in broadband helix traveling wave tubes (HTWTs). The research delves into the beam-wave interaction (BWI) performance of HTWTs under different hollow electron beam conditions. The theoretical analysis includes the use of gain parameter $C$ and space charge parameter $QC$ to evaluate the performance within the linear interaction region. Based on the analysis, a 4–20 GHz ultra-wideband traveling wave tube (TWT) based on a hollow beam scheme was designed using the software microwave tube simulator suite (MTSS). The design process involved optimizing the slow wave structure (SWS), the BWI performance, the electron gun, and the magnetic system. An output power greater than 109 W is achieved, and the small signal gain is better than 23 dB across the entire operating bandwidth. The particle-in-cell (PIC) solver in CST was used to verify the saturated gain of the designed TWT.

Electromagnetic metamaterials possess characteristics such as having large-scale, periodic, multi-media, and complex geometric structures, making them highly suitable for simulation using the finite element domain decomposition method (DDM). This work proposes a non-conformal DDM for simulating finite-period metamaterials, achieving simulation with a minimal number of domains while significantly reducing computational resource consumption. First, the computational domain of the periodic metamaterial is partitioned into several non-conformal hexahedral subdomains. Subsequently, a limited number of non-repetitive subdomain models with non-matching grids are constructed, leveraging the three-dimensional rotational and translational properties of these subdomains to facilitate simulation. By eliminating the necessity to construct models for every subdomain, a substantial reduction in memory consumption is achieved. Second, an iteration method for solving the matrix equations of subdomains is enhanced by introducing a multifrontal block incomplete Cholesky decomposition preconditioner, thereby enhancing the computational efficiency of matrix equations with a large number of unknowns. Meanwhile, parallel computing techniques are employed to accelerate the proposed method. Finally, we integrate the aforementioned method into a solver and leverage it to develop an electromagnetic simulation tool tailored for metamaterials. The tool is employed to simulate metamaterial structures of varying scales, resulting in notable reductions in both memory and time consumption while maintaining accuracy comparable to commercial software.