Iet Microwaves Antennas & Propagation最新文献

A highly miniaturised electrically small square loop antenna has been designed for operation at 2.5 GHz. The antenna is loaded using a simple series combination of two lumped inductors and two interdigitated capacitors in order to realise inherent impedance matching at a given miniaturisation level with respect to a specified source impedance, without using any external matching network. The designed antenna has an overall size of 0.061λ₀ × 0.061λ₀, which is approximately 75.6% miniaturised in terms of total loop length and 94% miniaturised in terms of overall footprint. The designed antenna is fabricated and the corresponding impedance matching and radiation patterns are measured, which are found to be in reasonable agreement with their simulated counterparts. Moreover, an investigation with two closely spaced electrically small SLAs, one for transmitting and the other for receiving, is carried out in this work in pursuit of maximising the isolation, which plays a crucial role in the Tx/Rx systems.

The electronic beam steering in conformal phased arrays is formed by exciting the multiple antennas with appropriate phase shifts. However, the malfunctioning of phase shifters connected to the central antenna elements in the conformal array distorts the radiation pattern of the array system severely as compared to edge elements resulting in the reduction of the array gain and increase in the side lobe levels. Here, the authors propose a non-dominated sorting multi-objective particle swarm optimisation (NS-MOPSO) technique capable of recalculating the independent phases of working antenna elements in the array in such a manner as to correct the overall radiation pattern. To illustrate the radiation pattern's recovery capabilities of the optimisation technique in case of malfunctioning of any random phase shifter(s), a 1 x 7 microstrip patch antenna array operating at 2.45 GHz on a wedge-shaped conformal structure was designed in CST simulator. To test, the radiation pattern's recovery capabilities of the NS-MOPSO approach, phase shifters connected to the antenna elements in the array were made to malfunction. Then the optimisation algorithm recalculates the phases for individual antenna elements to achieve the desired corrected radiation pattern. The simulated and measured radiation pattern recovery results are in good agreement with each other.

New coupling scheme substrate-integrated waveguide (SIW) diplexers based on dual-mode cavities are proposed for millimetre-wave applications. Dual-mode SIW cavities are simultaneously employed in common input and coupling cavity to produce filtering transmission poles and transmission zero (TZ). A common input SIW cavity with two orthogonal modes is employed instead of the traditional T-junction for circuit miniaturisation, insertion-loss reduction, and intrinsically high isolation. A critical dual-mode SIW cavity with diagonally distributed modes has been employed in each channel to realise a controllable stopband TZ for high selectivity of passband's skirt. To further improve channel isolation and passbands' selectivity, a SIW diplexer based on dual- and single-mode cavities is proposed, and four-pole responses for each passband channel are designed. For the verification, two millimetre-wave diplexers have been fabricated and tested.

An S-band near-field focused array is designed and implemented. Consisting of 4 × 4 metallic Vivaldi elements, the array is designed for focusing the E-field of several kilovolts per metre within its near-field region. To minimise the power loss and enhance the synthesis effectiveness, elements are arranged on a sphere surface and oriented towards the sphere centre. When exciting the elements, the waves will be focused to a specific area on the observation plane. By adjusting the excitation phase, the focus position can be tuned. A systematic analysis has been carried out to illustrate the focus scanning process across the entire observation plane. Near-field two-dimensional scanning is performed to measure the E-field distribution of the array. While scanning the focus, the diameter of 3 dB focal area is about 0.3 m, and the maximum field strength in the focus ranges from 1184 to 2129 V/m, which can be used for the radiated susceptibility testing.

Mutual coupling among multiple antennas has been a problem needed to be tackled in multiple-input-multiple-output (MIMO) systems. A decoupling method based on short decoupling feeding lines (DFLs) for MIMO patch antennas is proposed. The decoupling method utilises the feeding transmission line to create a new coupling path between the closely placed patch antennas. By adjusting the intensity and phase of the introduced new coupling, the original coupling can be cancelled out. The proposed method can realise both E- and H-plane decoupling. A 1 × 2 H-plane MIMO patch antenna array is first presented to explain the decoupling mechanism. Then, two practical examples of 2 × 2 and 4 × 4 MIMO patch antenna arrays are designed, fabricated and measured. The results indicate that the port isolation can be apparently improved from 15 to 38 dB for H-plane coupling and from 19 to 35 dB for E-plane coupling at the centre frequency of 3.5 GHz. Moreover, the proposed method is promising to be applied in arrays with other antenna type by adjusting the position and size of short DFLs.

A dual-band shared-aperture antenna array is presented, involving a combined scheme to suppress mutual coupling interference. The proposed array is comprised of a low-band (LB) antenna, a frequency selective surface (FSS), sixteen high-band (HB) antennas, and a reflector. The LB antenna utilises electromagnetic transparent (ET) characteristics to minimise scattering interference, while the FSS isolates resonance interference and port signal interference. The combined scheme integrates the benefits of both the ET antenna and FSS to suppress mutual coupling interference effectively. A prototype of the proposed antenna was fabricated and measured, operating at 1.7–2.7 GHz and 3.3–3.9 GHz. The simulated and measured results demonstrate stable patterns for both the LB antenna and the HB antennas. The cross-band isolation is higher than 28 dB in the low-band. With these advantages, the antenna array is suitable for base station applications.

The wide-angle electromagnetic scattering problems can be rapidly solved by using the method of moments in conjunction with compressive sensing theory. The method mainly has two computational parts: measurement and recovery. To further enhance the performance, an improved orthogonal matching pursuit algorithm with a randomised atom selection process is proposed, significantly reducing the computational complexity of the recovery part. Additionally, a restart mechanism is designed to eliminate possible errors that might occur during the random process, ensuring the accuracy of recovery results. Numerical experiments with objects of different shapes validate the effectiveness and efficiency of the proposed scheme.

Very-low-frequency (VLF) transmitting antennas have a crucial influence on the nearby electromagnetic environment. Commercial software packages, such as CST Studio Suite (CST) or Altair FEKO (FEKO), are always utilised to calculate the electric fields of VLF antennas, which consume considerable computing resources and time. The classical method of electric field calculation, the charge simulation method (CSM), is first applied to the calculation of electric field near the VLF transmitting antenna. The distribution characteristics of three-dimensional electric fields were analysed. The electric field surrounding the antenna exhibited axial symmetry. The highest electric field strength was at the top of the antenna, and as the distance from the antenna increased, the electric field strength exponentially decreased. The comparisons are performed between the results of the CSM and those of commercial software, the average relative errors of CSM on two observation paths are very small, 2.20% and 2.21%, respectively. Meanwhile, the CSM shows considerable advantages in saving calculation resources and improving efficiency. Additionally, the comparison between CSM calculation and the measured data is carried out. The results show that this method can accurately calculate the electric field near VLF transmitting antenna and offer valuable insights and a new solution.

The accurate prediction of radio wave propagation along highways plays an important role in the design of high-speed highway communication systems. The open-confined mixed space is a connection zone between the open space and confined tunnel along the highway. A hybrid propagation model is presented based on ray-tracing (RT) and waveguide theory, for the efficient modelling of open-confined mixed space. The proposed model employs RT to predict radio waves emitted by sources with arbitrary radiation patterns in open space sections, and utilises the waveguide theory approach to accelerate the prediction process in the confined tunnel sections. Both two-ray and six-ray RT models are included to take into account the suburban and urban environments. Numerical results are compared with simulated results generated by RT as well as experimental measurements. The validity and usefulness of the proposed model are demonstrated in an actual open-confined mixed space environment.

The needed isolation between elements for high-performance beam steering array antennas is a challenging task especially when the distance between the antenna elements is reduced. To tackle this problem, the authors report a multi-port multi-mode single-antenna with beam steering capability (±7 deg) suitable for cellular communications. The multi-port multi-mode characteristic of the proposed antenna enables size reduction and better taper efficiency than antenna arrays operating in the 3.3–3.7 GHz cellular band. The reported antenna exploits four Transverse Electric modes to modify the half-power beamwidth of the radiation from 20° to 41° as required in cellular communication.