Iet Microwaves Antennas & Propagation最新文献

This work introduces the biconical cavity as a high-performance resonator for multimode wideband bandpass filters. Unlike conventional cylindrical cavities, its tapered geometry enhances mode separation and extends the rejection band compared to an equal-order cylindrical cavity of the same configuration without additional tuning elements, while maintaining compact size. To verify this advantage, quadruple- and quintuple-mode bandpass filters using biconical cavities are directly compared with equivalent cylindrical implementations. Both quadruple- and quintuple-mode filters using biconical cavities are designed, fabricated and measured. The quadruple-mode filter operates at 3.82 GHz with 46.8% fractional bandwidth and three transmission zeros, whereas the quintuple-mode filter achieves 67.2% bandwidth at 3.52 GHz with four transmission zeros. Close agreement between measured and simulated results confirms improved stopband suppression and stable passband matching, establishing the biconical cavity as a compact and practical alternative for next-generation wideband communication systems.

This paper proposes a novel phased array which has outstanding advantage of broadband, miniaturisation and wide-angle scanning. First, leveraging a conventional antipodal Vivaldi structure enhanced with microstrip line side-feeding, resistive loading techniques and top-loaded radiating patches. Then, wide-angle impedance matching and stable scanning performance are realised by incorporating a dielectric matching layer above the radiating element and introducing dummy elements at the array edges. Additionally, elliptical parasitic patches are integrated to suppress gain fluctuations during beam scanning. Finally, a miniaturised 6 × 10 finite array is fabricated and measured. Both simulated and measured results indicate that the array maintains an active voltage standing wave ratio (VSWR) below 2.5 across a 4:1 bandwidth (2.1–8.4 GHz), supporting scan coverage up to ± 60° in the E-plane and ± 50° in the H-plane. The gain fluctuations at key frequencies is constrained within 3 dB throughout the scan range. Therefore, the design achieves a comprehensive property of low cost, compact size, ultra-wideband operation, wide-angle impedance matching and wide-angle scanning. This design demonstrates great potential for space-constrained applications, particularly in airborne multifunction radar systems.

An innovative deep-learning driven convolutional perfectly matched layer (CPML) integrated into the hybrid implicit-explicit finite-difference time-domain (HIE-FDTD) method is proposed to improve the efficiency of open-region electromagnetic simulations. The Autoformer neural network is introduced to replace the conventional multi-layer CPML structure. Both the computational domain size and algorithmic complexity are reduced since only a single-layer boundary layer is involved in the new model. Benefiting from the time series decomposition and sparse attention mechanism, the wave absorption efficacy of the proposed model is significantly improved without backward cumulative errors. Through a column-stacked data acquisition approach, the Autoformer-based CPML is compatible with both the FDTD and HIE-FDTD frameworks. The time step size of this proposed method is only determined by the coarse grid size, thereby extending the applicability of intelligent absorption boundaries beyond traditional FDTD limits. Numerical examples demonstrate that this method markedly improves computational efficiency while maintaining excellent wave absorption performance. Additionally, results confirm the method's robustness in complex scenarios, including multi-material, multi-source and multi-scale environments.

In this work, a graphene-based tunable phase shifter is proposed which deploys a semiautomated procedure for graphene deposition leading to a high-quality graphene transfer. The deposited graphene's complex impedance values are extracted from measured transmission coefficient values in the X band. Analysis of different widths of graphene is performed for better understanding of the microwave properties of graphene. It is evident that by decreasing the width of graphene, the impedance of graphene decreases, making it more conductive for lower widths. In order to observe the microwave tunable behaviour of graphene, varying DC biasing voltages are applied and the variation of transmission coefficients are measured. From the extracted values of complex impedance of graphene, it is observed that graphene possesses significant reactance variation, something that is not considered in literature. The reactance variation can be exploited in the variation of the phase of microwave signals. The reactance variation of graphene is further enhanced for increased phase variation by deploying it with an Interdigitated Capacitor (IDC). The IDC graphene phase shifter provides a phase variation of 60° with negligible amplitude variation at 9 GHz.

This article presents a coplanar stripline (CPS) reflectionless filter that integrates out-of-band absorption, exploring a novel configuration that promotes applications of reflectionless filters. By taking advantage of the CPS structure, the CPS absorptive resonator is initially proposed and studied to keep lossless transmission at its resonance and produce sufficient absorption at complementary frequencies. Next, a wide passband is achieved when introducing broadside coupling between two back-to-back CPS absorptive resonators. To guide the design, a transmission-line model representing the wideband CPS reflectionless filter is developed so that the wideband synthesis can be used to obtain all the circuit parameters for the specified transfer function. Subsequently, a 4th-order prototype is implemented. Simulated results reveal the filter achieves good impedance matching across the entire band with significantly reduced out-of-band reflection. Finally, the prototype is fabricated with transitions at its external ports. The de-embedded results in measurement are found in good agreement with the simulated ones, validating its compact size, wide reflectionless range, and efficient design process.

This paper proposes a polarisation-insensitive absorptive metamaterial unit cell that achieves a perfect absorption of circularly polarised (CP) incident waves. To overcome the miniaturisation limitations inherent in conventional metamaterial designs, an innovative approach employing a sandwiched configuration with cladding layers is introduced. This approach approximates perfect electric conductor (PEC) boundary conditions, enabling the truncation of the bulky periodic structure into a one-dimensional wall-type absorptive metamaterial (WAM). To mitigate mutual coupling under stringent aperture constraints, four WAM screens are integrated concentrically around the central element of a compact five-element array antenna featuring sub-wavelength element spacing (0.4λ) at the GPS L1 frequency. Both simulations and experimental results demonstrate inter-element mutual coupling suppression of less than −23 dB between the central and peripheral elements, alongside a peak realised gain improvement exceeding 3 dB for the central element. The WAM-enhanced adaptive five-element array achieves a maximum improvement of 4 dB in anti-jamming capability.

In order to verify the feasibility of atmospheric duct inversion method using automatic identification system signal in the actual sea area, a sea experiment was carried out. The signal acquisition system of portable high sensitivity civil automatic identification system is developed, and the receiving and processing process of automatic identification system signal is analysed. The sea experiment scheme and main experiment equipment are given, and the collected experiment data are processed and analysed. Finally, the method of atmospheric duct inversion using automatic identification system signal is verified by the measured data. Atmospheric duct inversion is an inverse problem, which requires the use of various optimisation algorithms to optimise the duct parameters in order to obtain the characteristic parameter information of the duct. In this paper, the Lévy flight quantum-behaved particle swarm optimisation algorithm and the deep learning algorithm are respectively used to invert the atmospheric duct parameters. The results show that there is little difference between the inverted duct parameters and the true duct parameters, which verifies the feasibility of using the automatic identification system signal to invert the atmospheric duct.

Microwave absorbers play a critical role in controlling electromagnetic wave propagation, especially in stealth technology and EMI shielding applications. In this work, we introduce a novel microwave absorber design inspired by the Sakarya chaotic system, which offers broadband and enhanced absorption properties. The proposed absorber structure exhibits distinct fractal geometries that enhance polarisation and angular stability using chaotic attractor-based patterns. The design process entails generating chaotic datasets from the Sakarya attractor, transforming them into fractal patterns via the Julia set, and fabricating the final structure using resistive ink by a screen printing method on an FR-4 substrate. Numerical simulations and experimental measurements verify the high absorption efficiency of the structure over a wide frequency range, demonstrating the potential of chaotic attractor-based designs to enhance electromagnetic absorption performance and offer innovative applications in stealth technology.

A millimetre-wave (mm-wave) microstrip patch antenna with a stable wide beamwidth is proposed for a wide-angle scanning phased array. The proposed antenna element is achieved by loading four semi-open parasitic elements around the stacked patch. The four semi-open parasitic elements can generate two pairs of stable antiphase current radiation sources to achieve a stable rotated ‘8’-shaped pattern, which can obtain wide-beamwidth radiation patterns when it is synthesised with the broadside radiation pattern produced by the stacked patch. Further, the coupling between the parasitic elements and the driven patch producing the lower reflection zero is weaker than that between the parasitic patch producing the upper reflection zero. Therefore, the proposed antenna can achieve a stable wide beamwidth over wide frequency ranges. The generation of the rotated ‘8’-shaped pattern is theoretically analysed. An eight-element E-plane scanning linear antenna array based on the proposed antenna element is demonstrated for the potential application in a wide-angle scanning phased array. The simulated and measured results show that the main beam can scan from −75° to 75° with a gain fluctuation < 3 dB under a 10-dB fractional bandwidth of 16.7%.