Iet Microwaves Antennas & Propagation最新文献

A novel design method of dual-band single-layer substrate-integrated waveguide (SIW) filtering antennas with independently controllable bands is proposed in this paper. The basic two-pole dual-band filtering antenna is proposed by a dual-mode rectangular SIW cavity coupled to two single-mode SIW cavities with respective radiating slots. Single cavity multi-mode is realised by etching dumbbell-shaped slots and metallised vias to achieve the purpose of broadening bandwidth and miniaturisation. The dual-mode SIW cavity acting as a common structure is fed by a coaxial feeder. The two orthogonal modes are coupled to two single-mode cavities by coupling windows to produce two two-pole passband filtering responses, respectively. Metallised vias in radiating SIW cavities are employed to realise good impedance matchings in radiating pass-bands. The two filtering radiation bands can be controlled independently, which is analysed in detail. Based on the basic two-pole dual-band filtering antenna, three- and four-pole dual-band filtering antennas are further proposed and analysed. For demonstration, two-, three- and four-pole dual-band filtering antennas with two centre frequencies of 10 and 11.7 GHz are designed, fabricated, and measured. The good agreement between the simulated and measured results verifies the proposed design methodology of single-layer SIW dual-band filtering antennas.

The Airborne Warning and Control System (AWACS) are pivotal assets in aerial operations, necessitating specialised protection measures, and serving as prime targets for enemy anti-radiation missiles (ARMs). This paper explores approaches to enhance the battlefield survivability of frequency diverse array AWACS (FDA-AWACS) by incorporating airborne radar technology onto the platform. The study commences by analysing the typical operational methods of anti-radiation missiles. Following this, a deception model is formulated for the frequency diverse array (FDA) against the passive radar homing head of anti-radiation missiles utilising the adjacent antenna single-pulse amplitude-comparison direction-finding technique. Expanding on this groundwork, the research further assesses the deceptive impacts of FDA-AWACS on direction finding cross-location techniques. Simulation results validate that FDA-AWACS can effectively counter the threat of anti-radiation missiles by diminishing their direction-finding and positioning systems.

This paper introduces a conformal frequency selective surface (FSS) with dual passbands from 9 to 9.3 GHz and 13.1–13.7 GHz, as well as one stopband from 10.4 to 10.9 GHz. The frequency response of the curved FSS coincides with the performance of the planar FSS with the same unit cell under normal incidence. The unit cell comprises two compact flower-shaped metallic slots patched on the dielectric substrate. This design has excellent stability of the incident angle up to 70°. The equivalent circuit model considering the mutual coupling between the two slots is illustrated to analyse the resonance mechanism. The whole antenna system enclosed by the conformal FSS is simulated to evaluate the loss in the far-field beam's directivity and aberration. The impact caused by the different curvatures is investigated. The samples in planar and elliptic cylindrical surfaces are fabricated. The insertion losses of both polarisations are less than 1.5 dB, as the angle of incidence varies to 60°. The frequency response of curved FSS is identical to the planar FSS under normal incidence. The maximum attenuations of both polarisations in the passbands are less than 1.38 dB, and the average transmission coefficient in the stopband is −22 dB. The conformal FSS brings slight aberration in the half power beamwidth (HPBW) of the incident beam in the passbands. Furthermore, it suppresses the main beam in the stopband by at least 25 dB.

Semi-analytical design approach to electrically small, dual-mode resonant, wideband circularly polarised (CP) microstrip annular sector patch antenna (MASPA) with variable polarization is proposed for satellite-assisted Internet-of-vehicle (IoV). At first, the upper bound of electrically small patch is theoretically laid down by advancing an interpolated algorithm to the eigen-roots of the characteristic equation, so that the radius of patch can be rapidly determined in the initial design step. In this way, MASPA with electrically small patch, multimode resonant, and frequency scannable CP angle can be yielded. Dual-mode resonant MASPAs with flare angles of 330° on air substrate, and 270° on suspended microstrip air/F4B substrates having a profile less than 0.05-wavelength are then numerically studied and experimentally validated. In the suspended microstrip case, MASPA with maximum patch radius of 0.159-wavelength (electrically small), equal impedance and tilted CP bandwidths up to 26.6%, and tilted CP angle of θ_t = −10°–35°, has been successfully implemented. Therefore, the proposed approach should be highly effective for low-profile, electrically small, wideband CP antenna designs.

This paper demonstrates a miniaturised frequency selective rasorber (FSR) that incorporates meander cross-rings to realise a wide transmission band. The FSR comprises a resistive layer and a bandpass frequency selective surface (FSS), which are separated by an air layer. The resistive layer is constructed by employing meander cross-rings equipped with lumped resistances, where the inner arms of cross-rings are bent to obtain a parallel resonant circuit with large inductances and small capacitances to achieve broadband transmission at high frequencies. The bandpass FSS is implemented using a triple-layer metallic structure, where two identical square ring layers are coupled through a central metal grid layer to form the transmission band. The measured results indicate that the absorption band with absorptance exceeding 90% is from 3.5 to 9.4 GHz, and the passband exhibiting insertion loss of less than 1 dB spans from 11.92 to 17.98 GHz with a 40.5% relative bandwidth, which matches well with simulated ones. This FSR has the characteristics of simple structure and high performance, which provides a novel concept of stealth applications.

In this paper, an electronically 1-bit reconfigurable reflectarray antenna (RRA) with wide-angle beam-scanning and high efficiency performance is presented for formation satellite communication applications. A 1-bit phase distribution can be generated by controlling the state of the PIN dipole in the configurable element comprising a double split ring (DSR) patch and two T-shaped parasitic structures. The resonant frequency of the DSR patch in both states can be optimised by a T-shaped parasitic structure, which is beneficial to improving the bandwidth and aperture efficiency. A 180° ± 20° phase difference can be realised from 9.7 to 10.3 GHz only by controlling one PIN dipole loaded on the proposed element, which ensures stable radiation performance over a larger band. To validate the effectiveness of the proposed element, a prototype RRA containing 20 × 20 units is designed and measured. A ±60° beam scanning range with the gain drop of 3.2 and 3.3 dB in the xoz and yoz planes is realised, which verifies the wide-angle beam-scanning ability of the RRA. The measured peak gain is 25 dBi at 10 GHz in the broadside direction, corresponding to an aperture efficiency of 25.2%. Meanwhile, the 1-dB gain bandwidth of the proposed RRA is 12.6%.

This paper introduces an efficient method of moments (MoM) designed to explore electromagnetic scattering in multilayered anisotropic structures. Each layer is made up of a dielectric anisotropic material characterised by a generalised tensor for permittivity, which is unrestricted in its geometrical configuration. The authors’ approach analyses each layer independently, employing the surface equivalence theorem to substitute the interfaces between layers with suitable equivalent electric and magnetic surface current densities. The authors derive the necessary surface integral equations (SIEs) for each interface by implementing the proper boundary conditions. The analysis utilises rotated dyadic Green's functions that populate the infinite space with the material properties specific to each anisotropic layer. The rotation angle corresponds to the deviation between the local principal coordinate system of the material and the global coordinate system, which is determined by diagonalising the full dielectric tensor of the respective anisotropic material given in the global coordinate system. To address the SIEs for determining the unknown equivalent electric and magnetic surface current densities, Galerkin's MoM is applied. This involves expanding the unknown surface currents using suitable basis functions, simplifying the issue to a matrix equation solved through the inversion of a block-tridiagonal impedance matrix. The diagonal nature and sparse structure of the impedance matrix, along with an effective block-inversion method, significantly boost computational efficiency and reduce memory demands. To demonstrate the feasibility of the proposed method, the authors present a detailed derivation of the impedance matrix for the case of non-magnetic uniaxial anisotropic media for which the Green's functions are available in closed form. The validity and efficiency of the proposed SIE-MoM scheme are demonstrated by comparing the results of several case studies against those found in literature and results obtained via commercial numerical codes.

This paper presents the design of novel compact multifunctional coaxial to waveguide power combining transition (PCT) for X-band applications. For the proof of the proposed concept, 2-way PCT operating over the entire X-band (8.2–12.4 GHz) and 4-way PCT operation from 9.5 to 10.8 GHz are designed, developed, and characterised. Two-way PCT achieves a measured return loss better than 14 dB over the operating band, and the measured amplitude imbalance and phase imbalance are within 0.25 dB and 4°, respectively. Four-way PCT achieves a measured return loss better than 15 dB over the operating band, and the measured amplitude imbalance and phase imbalance are within 1 dB and 10°, respectively. Furthermore, a 6-way PCT is also designed, fabricated, and measured to demonstrate the scalability of the proposed concept. The 6-way PCT achieves the measured return loss better than 15 dB from 9.9 to 10.475 GHz, and measured amplitude and phase imbalances are within 0.6 dB and 10°, respectively. The designed power combining transition is proposed to be used in X-band applications like antenna array applications and power combining applications.

A novel broadband water-based Fabry–Pérot (FP) antenna with beam-steerable technology is proposed. The antenna consists of a water-based reconfigurable partially reflective surface (RPRS) and a source antenna. The proposed water-based RPRS has 13 columns of microfluidic channels inside. The water-based RPRS achieved 1-D beam steering by regulating phase distribution through the injection of water into its microfluidic channels. The antenna has exhibited a 10-dB impedance bandwidth from 5.07 to 6.46 GHz (a fractional bandwidth of 24.1%). This design achieves a beam steering from −11° to +11° in the elevation plane, with measured realised gains over 10 dBi. To verify the correctness of the design, an antenna prototype was fabricated. The measured results are in good agreement with the simulated results, confirming the accuracy of the design principle. The measured results demonstrate that the main beam of the antenna prototype tilts to −12° in the broadside direction.

Intelligent Reflecting Surfaces (IRS) enhance wireless communication by optimising signal reflection from the base station (BS) towards users. The passive nature of IRS components makes tuning phase shifters difficult and direct channel measurement problematic. This study presents a machine learning framework that directly maximises the beamformers at the BS and the reflective coefficients at the IRS, bypassing conventional methods that estimate channels before optimising system parameters. This is achieved by mapping incoming pilot signals and data, including user positions, with a deep neural network (DNN), guiding an optimal setup. User interactions are captured using a permutation-invariant graph neural network (GNN) architecture. Simulation results show that implicit channel estimation method requires fewer pilots than standard approaches, effectively learns to optimise sum rate or minimum-rate targets, and generalises well. Specifically, the sum rate for GDNNet (GNN + DNN) improves by $��12.57�\%�$ over linear minimum mean square error (LMMSE) and by $��12.42�\%�$ over perfect CSI concerning the number of users, and by $��28.57�\%�$ over LMMSE and by $��14.28�\%�$ over perfect CSI concerning pilot length. Offering a feasible solution with reduced computing complexity for real-world applications, the proposed GNN + DNN method outperforms conventional model-based techniques such as LMMSE and approaches the performance of perfect CSI, demonstrating its high effectiveness in various scenarios.