Iet Microwaves Antennas & Propagation最新文献

The increased demand for user device connectivity has led to spectral congestion which is driving exploration of higher frequency spectrum, such as millimetre wave frequencies. As millimetre wave propagation is predominantly line-of-sight, shadowing becomes prevalent in indoor environments due to obstructions from clutter. Accordingly, there is a need to find solutions which can provide additional coverage. In this work, octant-shaped spherical reflectors are deployed in small office environments with varying degrees of clutter to provide additional ray paths to improve millimetre wave coverage into shadow regions. Cost weightings have been allocated to prioritise regions of high importance and are used to compare reflector deployment strategies. Appropriate positioning of reflectors in the environment is shown to improve coverage into shadow regions in all three environments considered, with placement in the top corners of a room found to be a valid solution. In densely cluttered environments, more than one reflector may be required to provide sufficient coverage. Reducing the reflector radius by 0.1 m has been shown to increase reflected power by up to 6 dB in some cases.

This paper presents a compact, broadband, high-gain dielectric rod antenna. By utilising an air–dielectric hybrid method for designing the radiating and matching sections, gradual variations in the average equivalent permittivity along the rod are achieved, and the mechanism of the method is analysed. This approach facilitates a smooth impedance transition from the feed to the air, resulting in good impedance matching characteristics. Additionally, the antenna is fed through a tapered double-ridged waveguide (DRW) with a coaxial line to tapered DRW transition. The proposed antenna achieves an impressive impedance bandwidth of 90.2%, covering the entire K and Ka bands. The unique structure of the proposed dielectric rod significantly enhances the antenna's gain, reaching a maximum value of 17.86 dBi. With its small aperture and compact longitudinal dimensions, this antenna is suitable for applications in settings like the Space Environment Simulation Research Infrastructure (SESRI).

This paper proposes a single-shot computational imaging using a new frequency-diverse aperture, an open-ended cavity with a rough surface base. First, it shows that scattering from a conducting rough surface made of conducting cones placed at random positions on a conducting ground plane, normally illuminated by an ultra-wideband horn antenna (working in the 2–20 GHz range) provides random patterns with a frequency correlation function (FCF) width of Δf, about hundreds of MHz. Next, by introducing four conducting walls placed around the rough surface, it obtains a higher number of spatially uncorrelated radiation patterns and a narrower FCF width of about Δf/10, tens of MHz. To approximate the radiation patterns and measurement matrices in the numerical simulations, the geometrical optics (GO) approximation is used taking into account multiple interactions. On the other hand, to estimate them in practice, a trihedral corner reflector installed on an XYZ positioning table is employed. Finally, the image of a planar object with the shape of plus is reconstructed using the minimum least-squares technique. The paper shows that for a 0.81 square metre image size, a decent-focused image with a pixel size of about 0.81/400 square metres (about 5 cm × 5 cm) is realisable by using 400 frequency samples within the frequency range of 2–20 GHz.

In this paper, a 280–300 GHz hybrid-integrated transmitter is proposed. The advantages of the SiGe and InP chips are fully made use by integrating these two chips. For low cost and high integration, the local oscillator chain and mixer are based on chips in SiGe technology, and the 300-GHz power amplifier and on-chip antenna are realised in InP technology for high output power and small die size. The low-cost bonding wires are introduced for the interconnection between these two chips, and the lens are attached above the on-chip antenna for further EIRP enhancement. Finally, the proposed transmitter is fabricated and measured, which shows comparable performances with 21.9 dBm EIRP (equivalent isotropic radiated power) and 10 Gbps data rate.

This paper presents a systematic antenna design methodology that integrates machine learning, leveraging the progressive growth technique of Progressive Growing of GANs (PGGAN) to generate images of various dual-band PIFA-like antenna structures. The process involves using data augmentation methods to generate 4180 antenna samples. In the latent space, the authors employ Latin Hypercube Sampling to maintain diversity and combine it with the Hough Transform to enhance the edge features of the antennas while providing labelling functionality. This labelling method strengthens the relationship between antenna frequency and wavelength characteristics. The paper clearly outlines the design process, starting from the simulation of two types of single-frequency PIFA-like antennas (2.45 and 5.2 GHz, respectively) to the completion of PGGAN's generation task, resulting in a novel dual-band Wi-Fi PIFA-like antenna structure. The measurement results of the dual-band antennas exhibit excellent consistency with the simulation results.

This work presents a numerical technique for the analysis of the Radar Cross Section (RCS) of large targets combining macro-basis functions, the multilevel fast multipole method and the generation of near-field preconditioners, using an approximate inverse matrix where the sparsity pattern is dynamic and computed considering an upper memory threshold. In order to improve the scalability, a group of rows is computed using the same least squares matrix minimising the Frobenius norm of the error, rendering each row group problem independent from the rest. This approach is applied to large and realistic problems in the test cases included. The presented preconditioner can be used to optimise the convergence of complex problems with respect to the hardware resources available in each case while being transparent to the user.

This paper presents a direct design approach and explicit design formulas for a wideband quadruplet bandpass filter with a pair of transmission zeros. A filter can be designed based on a filter schematic composed of only transmission lines and a short-circuited coupled-line section. The electrical length of all lines including the coupled-line section is 90$��°�$. The impedances of all lines can be calculated by explicit design formulas given in terms of the normalised coupling values in a coupling matrix of a quadruplet filter, which differentiates this work from existing design approaches. A fourth-order filter example is illustrated for demonstrating the practicality of using the presented structure and design formulas. This paper also discusses the expansion of the presented direct design approach for higher-order filter designs.

The flexibility of the integral equation (IE) method is limited by the available numerical solutions with uniform-grid schemes. In this paper, a general numerical solution of the IE is presented to predict long-range low-frequency (LF) groundwave propagation over irregular terrain. The general numerical solution is re-derived with the aid of Legendre–Gauss quadrature and interpolation quadrature. The great advantage of the resulting algorithm is that it can freely use non-uniform grid sizes in the computation area without loss of accuracy. Numerical results in two surface types, including triangular mountain and actual terrain are used to demonstrate the performance of the presented algorithm. Furthermore, it is ascertained that the non-physical perturbations at long propagation ranges in the IE predictions are caused by the inherent uniform-grid schemes of the numerical solution rather than the several approximations in the derivation of the IE form.

The analysis of diffraction by a semi-infinite parallel-plate waveguide with partial material loading is rigorously carried out using the Wiener–Hopf technique for the H-polarised plane wave incidence. In solving the Wiener–Hopf equations, the authors apply the Modified Residue Calculus Technique (MRCT) to achieve highly accurate solutions. The scattered field in real space is explicitly derived by performing the inverse Fourier transform of the solution in the transform domain. Within the waveguide, the scattered field is represented in terms of the waveguide TM modes, while the external field is asymptotically evaluated by applying the saddle-point method to yield a far field expression. The authors present representative numerical examples of the radar cross section for various physical parameters and discuss the far-field scattering characteristics in detail. Comparisons with the E-polarisation are also given.

In this paper, a new arc-shaped meta-atom like a fishbone controlled by Pancharatnam–Berry (PB) phase is designed for a microwave band, which can yield a high-purity vortex electromagnetic (EM) waves ranged from 10.63 to 26.86 GHz (relative bandwidth of 86.6%) with an efficiency of more than 90%. A single-beam metasurface with $��m�$ = +1, −2 and +3 modes is designed, respectively. Finally, a prototype with $��m�$ = −2 mode is manufactured in order to prove the feasibility of the designed metasurface. It shows that the experimental results are in good agreement with the ones of the simulation, which verified the excellent performance of the metasurface. The metasurface has a series of edges such as ultra-broadband, high efficiency, high purity and low profile compared to the conventional metasurfaces, which have strong practical applied value and significance for wireless communication.