Iet Microwaves Antennas & Propagation最新文献

Ultra-wideband (UWB) systems utilise a broad frequency spectrum to achieve high data transmission rates and enhanced precision, creating a demand for specialised UWB antennas. Circularly Polarised (CP) antennas are considered essential for maintaining robust performance under varied environmental conditions. Among them, the crossed dipole is effective for UWB CP applications, but its relatively large size could limit its use in various systems. A miniaturised crossed dipole design employing the Koch fractal structure is proposed and the measurement results are presented. The prototype antenna achieved an effective bandwidth covering 88% of the frequency range from 1.4 to 3.6 GHz. Additionally, a 4 × 4 array using this design was tested in the same frequency band, demonstrating beam-steering capabilities up to 30°. The proposed antenna has demonstrated effective deployment in diverse communication systems and phased array applications within ultra-wideband (UWB) CP environments.

To get simultaneously sparse and constant modulus excitation to reduce the complexity of the array and the mutual effect of neighbouring elements, a novel algorithm via alternating optimisation-alternating direction of the multipliers method is developed. This method uses the total transmitting power as the objective function to optimise the sparsity and the amplitude of excitation simultaneously. Numerical results are provided to verify its effectiveness.

An analysis and design of a new slotted power divider/combiner (PDC) that utilises an oversized substrate-integrated waveguide (OS-SIW) is presented to enhance power handling capability (PHC). It is interesting to note that, the power capability tolerance can be increased by increasing the width of structure and thickness of the substrate, although it may introduce higher-order modes. The paper is focused on improving PHC of PDC that propagates only the TE₁₀ mode while preventing the propagation of higher-order modes. Additionally, the PHC of the proposed structure is studied in detail. The air breakdown or the corona effect is a physical phenomenon that limits the Peak Power Handling Capability (PPHC) of a device. In slotted microwave components, the corona effect plays a crucial role in determining the PPHC, and it is closely related to environmental conditions such as pressure. Another limiting factor is self-heating, which affects the device's Average Power Handling Capability (APHC). The slotted OS-SIW PDC is designed on Rogers RO4003 laminate with 32mil thickness, offering a low profile with an overall OS-SIW PDC area of 170 × 55 mm². The measured results of the fabricated PDC showcase a range of desirable features. Moreover, the proposed structure in power divider mode exhibits significant improvements in APHC compared to those of the conventional Substrate-Integrated Waveguides structures, with respective enhancements of approximately 8.26% at 10 GHz (with a Fractional Band Width of 58.3%). These advantages are highly beneficial and hold great potential.

The present article proposes a novel hybrid approach for addressing the synthesis problem of rectangular planar arrays under multiple constraints, through joint optimization of the weight function and the improved grey wolf optimization (IGWO) algorithm. Firstly, the grey wolf optimization (GWO) algorithm is improved by using tent chaotic mapping, nonlinear convergence factor, dominant wolf dynamic belief strategy, and opposition-based learning strategy to increase the population diversity and the ability to jump out of the local optimum. Secondly, the array elements are weighted using the weight function to generate the position distribution matrix, which reduces the thinned matrix optimization time and improves the optimization efficiency. Finally, the position distribution matrix is used to generate the thinned array, and the IGWO algorithm is applied to perform the sparse optimization with multiple constraints. The effectiveness of the method is verified through numerical simulation and full-wave simulation experiments, demonstrating its capability to enhance array antenna performance and reduce peak sidelobe level (PSLL). These experimental results hold significant engineering implications and provide valuable references for addressing the array distribution problem under multiple constraints.

A novel slow-wave half-mode substrate integrated waveguide (HMSIW) bandpass filter (BPF) is proposed based on spoof surface plasmon polaritons (SSPPs) with loading capacitive patches (LCPs). The bandpass characteristics are achieved by etching complementary SSPPs on the metal patches of the HMSIW. SSPPs exhibit a slow-wave effect, which effectively reduces the overall size of the filter. At the same time, using proper LCPs between the HMSIW metal via and the complementary SSPPs structure, the effective dielectric constant of the HMSIW can be changed, reducing the low cutoff frequency and further facilitating the miniaturisation of size. A prototype of the proposed filter is designed, fabricated, and measured. The measured results show that the proposed filter has the in-band insertion loss of 1 and 3 dB passband range of 6.4–9.8 GHz.

A novel synthesis design approach to multimode resonant, azimuthal null frequency scanning antennas (ANFSAs) coordinated by null-depth is presented. The antenna is composed of a principal radiator and an auxiliary one fed by different ports. A synthesis chart gauged by different null-depths is developed to determine the respective exciting amplitude and phase conditions for the principal and auxiliary radiators. As is theoretically demonstrated and numerically verified, the ANFSA can exhibit an adjustable null-depth varying from −12∼−30 dB. A three-port unequal-split power divider with the simplest configuration is properly designed, utilised and integrated to meet the oriented power and phase conditions. A prototype with in-band null-depth of −30 dB is designed, fabricated and validated in such a way that its available bandwidth can reach up to 32.7%, and the null can continuously scan from φ = 160°–275° in azimuth plane.

A series of fourth-order bandpass filters (BPFs) with compact footprints, broad bandwidth, high selectivity, linear phase and notched response are proposed. The sketch of these BPFs is in accordance with the combination of the eighth-mode substrate integrated waveguide (EMSIW) and dual-mode microstrip line (DMML) resonators. The DMML resonator is constructed by means of metallic via-holes and pad in the double-layered structures. Among them, the DMML resonator can provide two transmission poles. Besides, the cross coupling is introduced through the vertical slot or fan-shaped aperture in the dual-layered substrates. The coupling schemes of the proposed BPFs can introduce two transmission zeros in the vicinity of operating passband, and the coupled scheme also exhibits a relatively flat in-band group delay. Notched frequency responses have been obtained by exploiting the U-shaped resonator and folded-ring resonator embedded with the mixed EMSIW and DMML BPFs. To validate the conceptual design, the proposed BPFs are simulated, fabricated and measured. Both the simulation and measurement have reached to a satisfactory agreement.

A high-power, high-isolation, dual-polarised planar phased array antenna is presented. Based on a multi-layer microstrip structure, two sets of polarisation ports are fed through orthogonal slot coupling, achieving high isolation and low cross-polarisation. Double-layer radiation patches and cavity interlayers are used to expand the bandwidth and increase the gain. Metal vias are added around microstrip feeders and between array units to suppress surface waves, thereby improving the scanning performance of the phased array. A smooth gradient microstrip structure is designed to improve the power capacity while realising broadband impedance matching. The measured results show that in the 8–10 GHz frequency band, the isolation of the dual polarisation ports is greater than 50 dB, and the impedance bandwidth reaches 22.2%, with active VSWR <1.5 when not scanning. Both sets of polarisation can achieve 2-D beam scanning in the range of E-plane ±20° and H-plane ±40° without grating lobes, maintaining the scan loss below 2.4 dB, cross-polarisation below −20 dB and active VSWR <2. Each unit achieves a high gain of 7.4 dB and large power capacity of 5 kW; so the entire 8 × 8 phased array can achieve a main lobe gain of 25.5 dB and realise high-power directional radiation with the effective isotropic radiated power of 92.5 dBm. The proposed planar antenna has a low profile of 5.5 mm (0.17λ₀).

Single-input single-output (SISO) three-dimensional (3D) wideband indoor directional measurements collected in a factory environment and an office environment at 38 and 70 GHz are presented. 3D single-input multiple-output (SIMO) dual polarised measurements with 1 × 2 antenna configurations were also carried out in a meeting room, a conference room, and an office room at the 60 GHz band. The measurements cover both azimuth and elevation by rotating the directional antenna (RDA) at the receiver side. Different statistical channel parameters such as power delay profile, power angle profile, root-mean-square delay spread, angular spread, and path loss were estimated for different possible antenna orientations between the transmitter and the receiver, which include line-of-sight, obstructed line-of-sight, and non-line-of-sight. The polarisation effects on path loss models and the delay and angular spread models based on the surface area of the environment are studied. The results will be valuable for the design of indoor millimetre wave cellular networks.

The authors propose a novel yet simple way of passive beamforming using a liquid antenna. A hemispherical dielectric resonator antenna filled with a dielectric liquid is considered to realise the fundamental TE₁₁₁ mode, and a small, weighted metal ball is dropped inside the hemispherical container. This metal ball functions as a movable director and passively steers the realised fundamental mode of the DRA always towards the ground. The proposed design finds its applications in static-subject-based applications such as indoor base stations, and beam-stabilisation/pattern-correction works in case of dynamic-subject-based applications. The overall profile of the antenna is 0.60λ₀ × 0.60λ₀ × 0.19λ₀ targeting the ISM band at 2.4 GHz with decent efficiency and far-field characteristics. The working prototype is developed and experimentally verified.