Iet Microwaves Antennas & Propagation最新文献

A low RCS (radar cross section) slot array antenna based on a liquid metal metasurface is proposed. The metasurface consists of 6 × 6 nested ring-shaped element. The inner ring with a checkerboard distribution can realise 180° ± 37° phase difference, which can effectively reduce the scattering performances for the slot array. The outer and inner ring together can excite more energy from the slot array, thus resulting in increased radiation gains. Therefore, by changing the layout of liquid metal on the metasurface, scattering and radiation enhancement modes can be switched. The measured results show that in the scattering mode, the RCS can be reduced from 8.1 to 17 GHz. While in the radiation enhancement mode, the proposed array with the metasurface can achieve a −10-dB impedance bandwidth of 9.4–11.2 GHz (17.4%) with a maximum gain of 8.12 dBi. Compared with the slot array without the metasurface, the realised gain is enhanced by 1.2 dBi from 6.9 dBi. The measured results correspond well with the simulated ones.

An approximation scheme that combines approximate solutions with error estimators to accelerate the adaptive h-refinement of the RWG-based method of moments (MoM) with the electric field integral equation (EFIE) is presented. The scheme is effectively implemented by using the near-field matrix to solve the approximate solution. Several conventional error estimators incorporated with the scheme are investigated. Compared to using the full MoM system, it significantly reduces the computational cost while maintaining the refinement effect. Numerical results indicate that the scheme could accelerate the adaptive refinement, yielding significant reductions in computational time and memory requirements.

The design of arrays capable of receiving wideband signals differs from arrays that can only receive narrowband signals. These arrays must be able to receive signals with an instant bandwidth of several GHz across the entire operating frequency, such as High-Resolution Radars or Terahertz in 6G communication systems. In these arrays, using a time delay line structure leads to an increase in beamformer coefficients, resulting in high computational complexity. This poses a challenge for beamforming in wideband systems. Additionally, classic Wideband beamformers face other factors, such as poor performance in the presence of input direction of arrival error, array calibration error, and requiring too many snapshots to reach the steady state of the beamformer. Therefore, the robustness of wideband adaptive beamforming using deep unfolding model-based technique is focused on, which has not been discussed before. The advent of deep unfolding, an innovative technique, amalgamates iterative optimization approaches with elements of neural networks. The aim is to deftly maneuver through various tasks across disciplines such as machine learning, signal and image processing, and telecommunication systems. Also, the network training method is done to become more robust against the mentioned factors. In the proposed structure, the constraints of the previous methods have been evaluated. It is observed to have better performance compared to other classic algorithms. Also, with the investigations of the proposed method with other conventional deep learning methods, it was observed that in some cases the proposed structure performance is equal to the conventional deep learning method and sometimes better.

A technique for wireless power transfer (WPT) efficiency improvement by a proper design of the excitation waveform is presented. This improvement is obtained on the one hand by a combined-harmonics excitation, and on the other hand by exploiting multiple-resonance coupled resonators. In contrast to wireless communications, there is no constraint on the linearity of the transmitter and receiver in a WPT system. Therefore, the impact of the excitation waveform on the power transfer efficiency with the help of an analytical model is investigated. An optimum excitation waveform is determined to maximise the power transfer efficiency. Thereafter, the authors concentrate on designing a multiple-resonance coupled resonator system that is consistent with the determined excitation waveform. This work introduces a non-uniform spiral resonator for controlling the self-resonant frequencies, which is consistent with the required excitation waveform. The performance of the designed coupled resonators is then evaluated using a 3D finite-element method and experiments. The numerical simulation and experimental results are in good agreement, verifying the validity of our design.

Lihong Wang, Jingya Yang, Chunhua Zhu, Dongsheng Zhang, Dan Fei, Yi Wang, Zhenghui Li, "Channel measurement and characterisation for 5G multi-scenarios at 26 and 38 GHz," in IET Microw. Antennas Propag. 17(14), 1042–1055 (2023). 10.1049/mia2.12421.

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A novel wideband dual-band bandstop filter with multi-transmission zeros and multi-reflection zeros is presented. It consists of two pairs of symmetric open-ended coupled lines at two sides and (2N − 1) pairs of coupled-line sections with an open-circuited stub in the middle. Through even- and odd-mode analyses, general simultaneous equations for characteristic impedances are derived with the proposed algorithm. By suitably selecting all the design parameters, the proposed topology could not only provide a controllable equal-ripple response in the passband but also control the stopband rejection, bandwidth (BW), and centre frequency ratio in the stopband flexibly. For verification, one prototype circuit is finally fabricated and measured in the experiment. Good agreement between the measured and simulated results is attained so as to successfully validate the correctness of the proposed design method.

A simple yet efficient solution to the problem of transverse electric (TE) scattering by a two-dimensional right trapezoidal groove placed in a perfect electric conductor (PEC) surface is presented. Using superposition of plane waves and applying the Neumann boundary condition at the groove walls, the transverse magnetic field is expressed as the sums of infinite series of waveguide modes. Considering the equivalent magnetic current on the aperture, a Fredlholm's integral equation with logarithmic singular kernel is extracted and then discretised by a collocation method based on a piecewise constant approximant. The extracted linear system of equations can be easily solved by the matrix methods for the unknown coefficients. Numerous examples are presented to verify the results and show the ability of the proposed method. Finally, this method is employed to examine the effect of the groove parameters and incidence angle on the scattering signatures.

This work investigates a switchable 4G/5G dual-antenna system designed for laptops. The dual open-slot antenna structure is straightforward, with a slot width of only 2 mm. Each individual antenna features two different feed sections located in two separate regions between the slots. Port 1 is a direct-feeding design with 3.6 pF chip capacitance, while Port 2 is only a direct-feeding design. When Port 1 is excited and Port 2 is terminated to 50-Ω, the antenna is functional in long-term evolution (LTE) low-band (617–960 MHz) and 5G sub-6 GHz band (3300–5000 MHz). On the other hand, when Port 2 is excited and Port 1 is terminated to 50-Ω, the antenna is functional in the LTE medium/high bands between 1710 and 2690 MHz. The measured isolation consistently exceeded 30 dB, and the efficiency remained above 48% across the entire frequency range. The calculated envelope correlation coefficients derived from the complex E-field radiation pattern measurements were consistently below 0.02. These findings indicate that the system is exceptionally well-suited for applications characterised by integrated metallic environments and a high display-to-body ratio.

The miniaturised wideband filter with good frequency selectivity and wide stopband is proposed, which is based on three-dimensional (3D) heterogeneous integrated passive device technology. The proposed sixth-order wideband bandpass filter is based on the magnetic-coupling-loaded highpass-lowpass lumped topology and implemented by the 3D heterogeneous integration process, integrating GaAs-based and Glass-based micro-nano-scale processes together. Then, lumped inductors are designed in the Glass substrate with low dielectric loss tangent and realised by a three-dimensional spiral structure. Therefore, the inductors have high quality factors and small sizes. The lumped capacitors are designed using the GaAs thin film process. Finally, a prototype with a 3-dB fractional bandwidth of 42% is designed and fabricated at 3.875 GHz (f₀). The upper-stopband attenuation higher than 30 dB is extended to more than 5.15f₀. It occupies only 0.014 × 0.018 λ₀² (1.1 × 1.42 mm²), where λ₀ is the free-space wavelength at f₀.

This article uses the ray inserting method to design a low-cost inhomogeneous lens in the Ku-band. The focal length to the diametre ratio of the designed lens is 0.45, which is lower than most designed lenses in this area. Also, no approximation is considered to yield the refractive index profile. The refractive index changes from the centre to the sides have been made in two sections to limit the maximum calculated refractive index of the structure to the Plexiglass refractive index. The designed lens proposed a good match to the source and surroundings. The theoretical design is validated by the finite difference time domain scheme and full-wave simulation. The lens structure is realised and fabricated on a multilayer Plexiglass sheet. The results of simulations and experiments indicate good performances of the designed lens in the wide frequency bandwidth.