Iet Microwaves Antennas & Propagation最新文献

A single-layered W band circularly polarised (CP) antenna array fed by a sequential feeding network using compact gap waveguides (GWs) with reduced pins is presented. The radiating element consists of a pair of cross slots and an open-ended rectangular cavity integrated into the top metal plate of the GW. A sequential rotation network (SRN) consisting of hybrid groove gap waveguide (GGW) and ridge gap waveguide (RGW) structure is presented. Due to the fact that conventional GWs with multiple rows of pins occupy large lateral size, thus making them difficult to realise a single-layered CP array fed by SRN. Compared with conventional GW with multiple rows of pins, compact GGW with a single row of pins is deployed here to make the presented SRN more compact, thus combining SRN and multiple CP radiators in the same layer. Particularly, a comprehensive investigation on the choice of the GGW groove depth is carried out. The groove depth is designed carefully such that the electric-field energy is more confined along the GGW line, and less rows of pins are required. For proof-of-concept demonstration, the proposed array has been fabricated and measured, exhibiting an overlapped bandwidth of 10.64% (89–99 GHz) and a peak gain of 19.48 dBi at 94 GHz. It presents a promising candidate for W band wireless applications.

In the anti-interference of broadband communication radio, interference cancellation performance is seriously affected by the uncertainty of the working frequency selection of the communication system and the direction of hostile interference. The closed-form solution of the interference cancellation weight value and the signal-to-interference noise ratio after the cancellation are derived and simplified to clarify the factors affecting interference cancellation quality. Then, the efficient blind area criterion is established for the low computational complexity in view of cancellation quality, which combines the radio communication index and anti-interference demand index. Based on this criterion, the minimum blind area model is proposed for robust performance. The experimental results in the auxiliary antenna spacing optimisation are consistent with the theoretical analysis, verifying the effectiveness of the proposed model in dealing with uncertain communication frequency and interference direction. It is very promising in communication interference cancellation.

A beamwidth (BW) and beam direction (BD) reconfigurable antenna based on multi-mode parasitic coupling is proposed. Two pairs of metal strips connected by only two positive-intrinsic-negative diodes are added as parasitic structures over the driven element, a circular microstrip patch, constituting a simple antenna design. By controlling the diode switching state, four pattern reconfigurable modes can be realised. Two beam-pointing deflection modes in the E-plane are realised based on the Yagi–Uda principle. Besides, the BW reconfigurability is achieved due to a joint effect of the Yagi principle and beam-stacking principle. All the reconfigurable modes share a 10% impedance bandwidth from 5.8 to 6.3 GHz. Simulation and measurement results show that the BW can be switched between 67° and 120° in an omni-directional plane, and the BD can be switched between 0° and ±30° in the E-plane.

A novel numerical method is introduced for minimising the presence of scattering echoes in the frontal area of a dielectric ellipsoid through the application of the method of auxiliary sources (MAS) method. This approach utilises a Gaussian radio pulse that spans the frequency spectrum from 0 to 6 GHz. The approach involves determining the properties of an ellipsoid, such as its dimensions and a dielectric permittivity, using a specially developed MATLAB software package to make this ellipsoid invisible. This provides a valuable military and defence technology tool, particularly for stealth and invisibility technology applications. It is beneficial for avoiding detection by radar systems utilised for enemy surveillance and identifying concealed objects. This aims to eliminate the need for metamaterials for invisibility cloaking. The suggested methodology has been confirmed through a validation process, which involved a comparison of the outcomes derived from numerical experiments conducted during pulse echo observations using the FDTD method and an analytical solution. MAS offers a notable advantage over other methods and commercial software by significantly reducing computational time for simulating and analysing 3D dielectric objects. This allows for quicker consideration of various parameter scenarios and optimisation for desired outcomes.

In the design and optimisation of marine wireless communication and navigation systems, a thorough investigation of radio wave propagation characteristics under atmospheric ducting conditions is essential. The authors aim to enhance the efficiency of radio wave propagation loss prediction in marine atmospheric ducting environments, proposing a prediction model based on Fast Reordered-Alternate Direction Decomposition (FR-ADD). By approximating the diffraction term into three independent components, exploiting the commutative properties of the Fourier transform to reduce the spatial dimensions, and incorporating a rapid algorithm for the parabolic equation, the model optimises the stepping process and significantly improves computational efficiency. Simulation experiments demonstrate that, in the long-distance and complex marine ducting environments, the model not only maintains prediction accuracy but also substantially reduces computational load and prediction time, effectively realising over-the-horizon propagation prediction. In the experiment of radio wave propagation characteristics in the Yellow and Bohai Seas, the simulation data from the FR-ADD model showed significant correlation with actual measurements and simulations from the AREPS software, confirming the method's efficiency and practicality.

The oversized TE₁₁ mode bend is able to make the transmission direction of electromagnetic wave to turn 90°, and it is one of the key components in the high-power microwave system. The mode coupling characteristics between the TE₁₁ and parasitic modes under two different polarisations in the bending waveguide are analysed, and it is found that the TE₁₁ suffers less interferences from parasitic modes when its polarisation direction is perpendicular to the bending plane, and the corresponding 90° TE₁₁ bend is easier to realise high performance. To verify this analysis, an oversized 90° TE₁₁ bend waveguide working at 10 GHz is designed, and its structural length is only 7.5 times the central working wavelength. Simulated results indicate that its relative bandwidth is 15.6% when the transmission efficiency is over 98%, and its maximum power handling capacity reaches 5.6 GW at short microwave pulse duration (less than 100 ns). The S-parameters indicate that its S₂₁ is about −0.1 dB from 9.5 to 10.5 GHz, and its S₁₁ is under −25 dB in the same frequency range. Meanwhile, the high power test indicates that the bend works stably when the injected power is 3 GW.

The authors propose a system of closely coupled-complementary frequency-selective surfaces (FSSs) based on the four-arms star geometry with dual- and triple-passbands responses for 5G applications. Four complementary structure configurations are presented, and depending on the chosen configuration, the structure can create two or three transmission bands in one or both polarisations of the electromagnetic waves. The designed FSSs are compact and have stable behaviour at different incident angles. The complementary FSS passes signals around 2.6 and 6.2 GHz, and a structural offset allows the transmission at a third frequency (4.2 GHz). To validate the proposed designs, four prototypes are fabricated and measured. Numerical and experimental characterisations are in good agreement.

The electromagnetic compatibility analysis of RF circuitry is essential due to the adverse effects on sensitive components. Two metamaterial unit cells with slow-wave properties are presented for cross-talk reduction in transmission lines. The analytical expressions for computing equivalent lumped elements of the lines are then provided. The dispersion diagram is obtained from the parameters extracted from the measurement. A microstrip as the generator line and five identical CRLH unit cells as the receptor line are then used and a significant reduction in cross-talk is observed in comparison to conventional lines. A non-uniform transmission line with two different CRLH unit cells as the receptor line is then employed and found effective in further cross-talk reduction between the lines. The lengths of the lines and numbers of cells are kept the same in all lines for comparison. The simulated results are validated by measurements.

Conventionally, both electrically larger (EL) arrays and sparse arrays offer the advantage of element number reduction but disadvantage of high sidelobe levels. A new scheme of planar EL sparse array antenna based on a genetic algorithm (GA) to achieve low sidelobe with element number reduction is proposed. To begin with, EL sparse array antenna optimisation models based on GA for both linear and planar arrays are analysed. Then, an EL slot antenna element based on a 3 × 3 substrate integrated waveguide cavity is designed. An 8-element linear EL sparse array antenna is designed and compared with a uniform array antenna, demonstrating a reduction in the maximum sidelobe level (MSLL) by nearly 4.6 dB. After that, a 4 × 8 element planar EL sparse array antenna is fabricated and measured. Compared to an 8 × 16 element planar EL uniform array antenna, the number of antenna elements is reduced by 75%, while the MSLL is reduced by approximately 3 dB. The measured −10 dB impedance bandwidth ranges from 25.3 to 27.8 GHz. At the central frequency, the radiation pattern achieves a peak gain of 29.6 dBi, exhibiting low sidelobe levels below −15.0 dB.

Traditional quarter-wavelength parallel-line couplers (QWPLC) in microstrip form suffer heavily in low directivity because of unbalanced even-mode and odd-mode phase velocities. Related schemes to improve directivity lead to complex structures and large dimensions. This study derives and validates an iterative synthesis method to design a high-directivity microstrip coupler adopting a symmetric stepped-impedance microstrip coupled line (SSIMCL). Given that the even-mode and odd-mode effective dielectric constants (EDCs) vary with the characteristic impedances, the authors take the EDCs of traditional QWPLC as the initial values for an SSIMCL, and the characteristic impedances and EDCs can be computed and converged in several iterations, resulting in good phase delay balance and high coupler directivity. A 20-dB microstrip coupler working at 1 GHz with high directivity is designed, fabricated, and measured. The obtained maximum directivity is 47 dB and approximately 1 GHz, while the relative bandwidth with a directivity higher than 20 dB and a return loss better than 20 dB is larger than 70%. The novel microstrip coupler also features a compact, simple structure shorter than λ_g/4.