Iet Microwaves Antennas & Propagation最新文献

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%.

In this paper, we propose a Double Pulse-based Dual Coprime Frequency Diverse Array Multiple Input Multiple Output (DCFDA-MIMO) radar for enhanced target parameter estimation, including range, angle, and Doppler. The proposed model employs an unstructured approach for parameter estimation using the recently developed DCFDA-MIMO radar, which has garnered significant attention due to its superior target resolution compared to traditional Frequency Diverse Array MIMO (FDA-MIMO) radar. Because most conventional designs rely on a structured approach using a single pulse, conventional FDA-MIMO radar suffers from increased computational complexity due to multiple signal classification (MUSIC) and strong coupling between range and angle parameters. To address these challenges, we introduce an efficient, low-complexity method that effectively reduces range-angle coupling and improves target parameter estimation. Unlike existing techniques, the proposed approach uses the Double Pulse method, transmitting the first pulse without frequency increments to estimate the angle. In contrast, the second pulse incorporates suitable frequency increments to estimate range and Doppler separately by incorporating the estimated angle information. Monte Carlo simulations validate that the proposed DCFDA-MIMO-based Double Pulse method significantly improves target parameter estimation in terms of signal-to-noise ratio (SNR), signal-to-interference-and-noise ratio (SINR), and Cramér–Rao lower bound (CRLB) compared to existing array structures.

The presented paper addresses the divergence issue of Nicholson–Ross–Weir (NRW) algorithm encountered during the electrical characterisation of half-wavelength or thicker low-loss dielectric materials. To overcome this limitation, an S₂₁-parameter-based extraction method is proposed for determining the complex permittivity of low-loss dielectrics in rectangular waveguide and free-space measurement environments at GHz frequencies. The iterative Newton method, supported by an initial guess, is employed for permittivity extraction. Explicitly formulated equations suitable for broadband iterative computations are presented. Measurements on a variety of low-loss dielectric material specimens in both rectangular waveguide and free-space measurement environments in X-band are demonstrated to ascertain the accuracy and stability of extraction procedure. Root-Mean-Square-Error (RMSE) calculations across the frequency band, along with comparisons to other reported extraction techniques are presented to demonstrate accuracy improvements. Furthermore, the uncertainties associated with the extracted complex permittivity in different measurement environments are analysed and discussed.

A wideband high-efficiency compact all-metal folded transmitarray antenna (CAMFTA) with integrated planar feed is proposed in this paper. It consists of a transmission metasurface (TMS) with the function of reflecting y-polarised wave, as well as transmitting x-polarised wave and twisting its polarisation by 90°, a linear polarisation conversion reflection metasurface (RMS), and a planar slotted patch as the feed. All these components are made of metal, making the entire structure relatively cheap to manufacture and resistant to stringent environments. Particularly, in addition to the low-profile nature of the folded structure, the metal-only planar feed is co-designed and integrated with RMS, resulting in a further reduced profile and a compact configuration. In order to validate the superiority of the design, a CAMFTA is simulated, implemented and measured at X-band. The results of experiments demonstrate a high degree of correlation with simulations, with peak aperture efficiency of 29% and 3 dB gain bandwidth of 13%, respectively. To the best of the authors' knowledge, this is the first CAMFTA reported in the literature, and it offers a number of advantages, making it very suitable for high-gain applications where a compact, low-cost, low-profile configuration with steady performance is required.