Iet Microwaves Antennas & Propagation最新文献

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.

This study presents the design, characterisation and prototyping of a novel all-dielectric artificial magnetic conductor (AMC) operating at 77 GHz. Unlike traditional metallic or hybrid counterparts, the proposed AMC is fabricated entirely from a commercial dielectric substrate, offering a low-loss and low-profile solution ideal for integration into compact antenna systems. The proposed AMC demonstrates strong reflection magnitude and achieves a 0° reflection phase at the targeted operating frequency. The −1-dB reflection bandwidth is 3.6 and 8.2 GHz for ± 45° and ± 90° phase windows, respectively. Integration with a dipole antenna confirms that the AMC maintains reflection phase stability under placement and fabrication tolerances. Measured results using a commercial material characterisation kit align closely with simulations, with deviations primarily attributed to substrate anisotropy at 77 GHz. Additionally, two alternative all-dielectric reflectors with high reflection magnitudes and nonzero reflection phases at 77 GHz are presented to support broader millimetre wave scenarios where in-phase reflection is nonessential. This work is among the first to report an all-dielectric AMC operating at millimetre wave frequencies while providing experimental validation, insights into anisotropy effects, fabrication constraints and real-world integration.

This paper addresses the issue of achieving excellent overall performance for frequency selective surface (FSS) radomes. A dual-layer frequency selective surface based on a hexagonal structure is proposed, which offers broadband suppression, roll-off characteristics, angular stability and a low insertion loss passband. The proposed FSS unit consists of two dielectric layers and a PMI foam layer, with conductive layers placed on both sides of the PMI foam. The FSS is composed of hexagonal ring units and three-level sub-centre units. This design achieves broadband suppression from 2 to 20 GHz, while maintaining a flat passband between 7.59 and 8.71 GHz, corresponding to a relative bandwidth of 10.8%. The transmission characteristics remain stable with incident angles ranging from 0° to 50° under both TE and TM modes. To validate the feasibility of the FSS design, a physical prototype was fabricated and tested. The experimental results show that the FSS performs well in broadband suppression, roll-off characteristics, flat passband and angular stability, in agreement with the simulation results. This demonstrates its strong overall performance and promising potential for applications in stealth antenna radomes.

This paper presents an energy selective reflectarray antenna with field-induced gain to prevent the high-intensity radiation fields (HIRF) in the X-band. Each unit cell of the reflectarray was anti-parallelled loaded with two diodes, the status of which could adaptively change the reflection phase according to the field intensity. When the diodes were all in the OFF-state, the unit cells in the reflectarray followed the gradient phase distribution, forming a high-gain beam; once there were diodes triggered by induced voltage caused by the high intensity incident wave, the gradient phase distribution was unsatisfied so that the reflected wave would be diffused and the gain would decrease. After full-wave simulation, the prototype was manufactured and measured in both the high- and low-intensity environments. The simulation and measurement results indicate that when the electric field strength is below 100 V/m, the achieved gain is above 25 dBi, the 1 dB bandwidth is 5.6% and the aperture efficiency is 29%; in the case of HIRF's illumination, the gain decreased by more than 20 dB within a bandwidth of 700 MHz. This dual-functional design holds significant promise for protecting sensitive payloads in aerospace platforms and improving signal integrity in radar systems exposed to electromagnetic interference.

This paper presents a new design of circularly polarised (CP) antenna with wideband and high gain selectivity. To achieve good circular polarisation performance, a wideband quadrature phase feeding network is initially developed with two output signals characterised by equal magnitude and consistent 90-degree phase difference. Then, to realise high gain selectivity, multi-mode resonators are introduced into the feeding network. Therefore, a specific filtering quadrature phase feeding network (FQFN) that integrates the functions of power division, frequency selectivity and phase shifting is successfully produced. Afterwards, a three-order FQFN operating at central frequency of 2.5 GHz is developed and measured for demonstration. As expected, the demonstrator has obtained wide impedance and phase bandwidths of 57.3% and 70.8%, respectively, together with two transmission zeros at about 1.25 and 3.75 GHz. Finally, a pair of crossed magneto-electric dipole antennas are implemented by adopting the proposed FQFN to achieve wideband CP radiation with high selectivity. Experimental results exhibit that the proposed scheme has achieved both impedance bandwidth of 65.3% and 3-dB axial ratio bandwidth of 62.4%, simultaneously. Moreover, attributing to the integration of the filtering function within the FQFN, performance of high gain selectivity is accomplished and ensured by three transmission zeros in gain response.