Iet Microwaves Antennas & Propagation最新文献

A double-layer wideband circularly polarised (CP) metasurface (MTS) antenna is proposed. The MTS consists of a 4 × 4 L-shaped patch array. The modal behaviours of the proposed MTS are investigated using the characteristic mode theory. Two characteristic modes with orthogonal current distributions are selected as the operational modes. Furthermore, an aperture-coupled feeding structure is employed to excite the two orthogonal modes with a 90° phase difference, enabling CP radiation. It can also excite the MTS to generate multiple resonances and axial ratio (AR) minimum points, which collectively yield an acceptable bandwidth for both impedance and AR. Finally, an antenna prototype is designed to validate the simulated results. The measured results show that the MTS antenna offers a −10 dB impedance bandwidth (IBW) of 34.9% (4.25–6.05 GHz), a 3 dB AR bandwidth (ARBW) of 13.2% (5.3–6.05 GHz) and a maximum gain of 7.3 dBic.

This paper presents a new approach to designing transmission line (TL) and power divider/combiner (PDC) using an oversized air-filled substrate-integrated waveguide (OS-AFSIW). Our approach enhances the average power handling capability and reduces the loss. By strategically increasing the width of proposed TL, we achieve improved power handling capability. However, this approach can introduce higher-order modes, which can be detrimental. Therefore, this paper focus on designing a balanced delta port magic-T PDC configuration within the OS-AFSIW that exclusively supports the fundamental TE₁₀ mode and effectively suppresses the unwanted higher-order modes. This paper conducted a thorough analysis of the proposed PDC's average power handling capability, resulting in excellent agreement between fabricated and simulated results. The OS-AFSIW PDC was implemented on an FR4 and low-profile Rogers RO4003 laminate with a thickness of 32 mil, resulting in a compact design with a footprint of 144.63 × 58.4 mm². The fabricated PDC exhibits outstanding performance characterised by input and output return losses exceeding 10 dB, good isolation across the entire Ku-band (offering a fractional bandwidth of 28.57%), and significantly reduced loss compared to conventional air-filled structures. Notably, at 15 GHz, our design demonstrates impressive improvements of approximately 35% in the loss and 17% in the Average Power Handling Capability (APHC), which is a significant advantage for practical applications.

This paper addresses the problem of surface wave confinement and the suppression of undesired transverse electric (TE) mode propagation inside the grounded dielectric slab when excited by the transverse magnetic (TM) slot launcher. As a solution, we propose a surface waveguide (SWG) design based on self-complementary Bowtie metasurfaces. Leveraging the concepts of TE soft and TM hard bandwidth operations, the SWG effectively confines TM surface waves while suppressing unwanted TE modes. We present an analytical model capable of calculating the Bowtie metasurface's reflection coefficient for oblique-incidence excitation. Additionally, a simple yet efficient electromotive force (EMF) algorithm is introduced for analysing the reflection phase for oblique-incidence excitation across a range of wavenumbers and frequencies. We use the proposed EMF model to calculate the TE soft and TM hard bandwidth operations of the Bowtie metasurface. We present a uniplanar, compact and wideband slot launcher to excite directed and well-trapped TM mode inside the SWG. We fabricated a novel Rotman lens based on the Bowtie SWG and slot launcher to further support our methodology. The SWG lens exhibits a $��\pm �$ 56° scanning range, similar to that of its microstrip lens counterpart while offering the potential for reconfigurability and suitability in millimetre-wave applications.

At present, researchers often focus on various aspects such as the meteorological conditions along the long-wave propagation path and the conductive characteristics of the Earth's surface, and analyse the long-wave ground wave propagation delay one by one. If a unified analysis and modelling can be carried out for the long-wave propagation delay affected by multiple factors, it will significantly improve its prediction efficiency and engineering implementation efficiency. Firstly, this paper conducts analysis from the time domain and the frequency domain, and discovers its obvious periodic time-varying characteristics. Based on this, a quadratic polynomial model with periodic terms is constructed and used as the first prediction model. Next, in order to improve the accuracy and make full use of historical data, the new predicted values are inserted into the sequence of measured values to construct a quadratic polynomial long-wave prediction model based on the sliding window and with periodic terms (Model 2). Finally, these two models are used to make predictions for different durations on the 7-day delay data. The actual measurements show that in the short term, the accuracies of the two models are equivalent, and when the prediction duration increases, the advantages of Model Two become more apparent.

To address the spectrum shortage in fifth-generation (5G) and future communication systems, multibeam antenna is a hotspot in recent years. 2-D multibeam antennas usually have limited coverage range and with high dielectric loss and cost. This letter proposes a low-cost 2-D multibeam transmitarray (TA) using the method of sliding effective aperture. By sliding the feeding source, the effective aperture slides accordingly. Different sources represent producing different equiphase planes and thus achieving multiple beams. For improved beamforming effect and transmission efficiency, a wide-beam 2 × 2 patch array serving as the feeding source and a four-layer Jerusalem cross slot acting as the TA unit cell with a 360° phase range are designed. Finally, a full-metal 2-D TA measuring 219.6 × 219.6 mm² is fabricated and measured. The proposed square TA can achieve a continuous beam converge of ± 41° in θ direction and ± 180° in φ direction, with the peak gains of 19.8–24.7 dBi. The measured results are in good agreement with the simulated ones. Compared with other multibeam antennas, the proposed square TA realizes high gain beam scanning and low manufacturing cost, which has great application prospects in modern communication system.

An X-band wide-angle scanning array with sidelobe reduction and low gain fluctuation performance is presented in this paper. The element of the array consists of a bent horizontal dipole and two coupled-fed vertical monopoles. By switching the states of the diodes integrated on the vertical monopoles, the superimposed radiation pattern of the horizontal dipole and the vertical monopoles can steer the main beam to −42°, 0° and 40°, respectively. Notably, when the element beam points at −42° and +40°, the element gain at +60° to +90° and −90° to −60° are decreased significantly, which can ensure the array has a low sidelobe level at large scanning angles. Based on the reconfigurable element, a 16-element array is constructed. Without the need for amplitude weighting, the proposed array can achieve beam scanning from −70° to 70° with a gain fluctuation of less than 0.8 dB while maintaining sidelobe levels below −11 dB. The results indicate that the proposed array has higher gain and lower sidelobe level than the traditional dipole array with the same aperture size. The proposed array has the advantages of simple structure, wide beam coverage, low gain fluctuation and low sidelobe level. These features enable its applications in base station and radar.

A compact phase-modulated transmissive metasurface (MS) lens is proposed to enhance the propagation performance of orbital angular momentum (OAM) vortex beams. The system integrates a compact circular ring phased array antenna (CRPAA) operating in the X-band to generate OAM beams and an MS lens designed using an optical converging axicon theory. The MS lens, measuring 4.17λ₀ × 4.17λ₀ × 0.169λ₀ (λ₀: centre frequency wavelength), modulates the phase distribution to focus OAM beams generated by the CRPAA, which has dimensions of 2.67λ₀ × 2.67λ₀ × 0.0372λ₀. When placed 60 mm (2λ₀) from the CRPAA, the MS lens significantly reduces the divergence angle of the OAM beam (mode l = −2) from 72° to 30° and increases the gain by 22%–89% across the operating frequency range. Additionally, the system maintains high OAM purity at a propagation distance of 150 mm (5λ₀), ensuring stable vortex wave emission. The compact design demonstrates significant improvements in beam focusing, miniaturisation and communication reliability, making it highly suitable for applications requiring precise OAM beam control and enhanced transmission performance. Simulation and experimental results validate the effectiveness of the proposed MS lens in reducing beam divergence and improving gain, highlighting its potential for advanced OAM-based communication systems.

The theory, design and experimental validation of a circularly polarised (CP) metamaterial fixed-beam leaky-wave antenna (LWA) with zero beam-squinting (ZBS) is presented in this paper. It consists of two oppositely directed negative-refractive-index transmission-line (NRI-TL) LWAs, which are fed through an NRI-TL 180$��°�$ balun. Each NRI-TL LWA generates its own beam and when the two beams, which radiate is opposite directions, are combined, they produce a fixed-beam over a wide zero beam-squinting bandwidth. This NRI-TL 180$��°�$ balun is specifically implemented to achieve CP radiation with enhanced gain at the broadside direction. Therefore, a detailed analysis of the NRI-TL 180$��°�$ balun is presented. Finally, the measurement results of a realised broadside circularly polarised fixed-beam LWA are presented and discussed. It is shown that the addition of the NRI-TL balun doubles the gain of the metamaterial LWA, since both orthogonal components, both co- and cross-polarisations are utilised providing CP and enhanced radiation gain and efficiency. The antenna's beam-squinting bandwidth is approximately 0.9 GHz, accompanied by an axial ratio of around 1.3 and exhibits an average radiation efficiency of 80$��\%�$.

A polarisation conversion metasurface (PCM) is proposed to realise broadband radar cross section (RCS) reduction of a slot array antenna. The PCM's unit cell, whose polarisation conversion ratio (PCR) is more than 88% from 8.41 to 32.28 GHz under x-and y-polarised normal incidence, consists of two pairs of v-patterns with gradually narrowing widths and a pair of rectangular patterns. The wideband RCS reduction of PCM is achieved by chessboard structure. Simulated and measured results prove that the application of PCM reduces wideband RCS. The proposed PCM can realise the RCS reduction outside the antenna's operating band. The 10 dB RCS reduction ranges from 8.7 to 34.8 GHz under normal incident wave with no polarisation insensitivity.

In this paper, a multi-layer waveguide (MLW) bandpass filter is realised by stacking thin metal layers at E-band. In order to eliminate the leakage between layers, an electromagnetic band gap (EBG) pin array is utilised. The periodic pin texture is created by 3D chemical etching on the layers. The thickness of layers and height of pins are selected properly to provide a stopband at operating frequency band of interest. A thin metal layer at the middle of the waveguide channel is used to realise the cavities and coupling slits of the filter. A seventh order metal-insert E-plane filter with frequency pass band of 69.5–76 GHz is designed and fabricated. The designed MLW bandpass filter is fabricated in brass and copper metal sheets with insertion loss of around 1.5 and 1.1 dB, respectively. Several filter prototypes are fabricated and studied to verify the repeatability of the fabrication and assembly processes.