Conventional multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) radar systems typically adopt the equidistant subcarrier interleaving (ESI) scheme to generate orthogonal transmit (TX) waveforms in the frequency domain. However, the ESI scheme is limited by a reduced unambiguous distance and distance-dependent angle errors. To mitigate these issues, this paper proposes a hybrid range- and Doppler-division multiplexing (RDM-DDM) scheme for MIMO-OFDM radar, which separates TX signals in both the distance and velocity domains. We first establish the signal model for the hybrid MIMO-OFDM radar system. At the receiver, we implement distance–velocity–angle processing using fast Fourier transforms (FFTs). Additionally, an ambiguous-cell Doppler correction algorithm is applied to mitigate intercarrier interference (ICI) and resolve velocity ambiguity. This hybrid scheme increases the number of virtual MIMO channels, eliminates distance-dependent angle errors, and enhances angle estimation accuracy. Furthermore, it overcomes the inherent limitations of standalone RDM or DDM, allowing for adaptive control of unambi guous distance and velocity by adjusting the hybrid ratio. Simulations based on a 77-GHz 8 × 8 antenna array configuration validate the effectiveness and superior performance of the proposed schemes.
Mathilde Mauger-Vauglin, Stéphanie Battiston, Mathias Studer
et al.
Cette étude approfondie de l'utilisation des données satellitaires Pléiades Neo dans la détection des dommages aux bâtiments, comparée aux données Pléiades-HR, s'est concentrée sur l'évaluation des performances de ces deux capteurs suite au séisme au Maroc en septembre 2023. Les résultats indiquent de manière concluante que la résolution spatiale supérieure des images Pléiades Neo améliore significativement l'interprétation du paysage et la détection des dommages dans les zones bâties. En particulier, ce gain en résolution a permis d'identifier 74% de bâtiments endommagés supplémentaires à Marrakech et de rectifier 24% et 11% de la classification des dommages, respectivement dans les secteurs de Marrakech et d'Imidal. L'étude souligne également la capacité de Pléiades Neo à détecter des détails du paysage urbain, comme les créneaux des remparts de la ville, offrant ainsi la possibilité de repérer des dommages sur d'autres objets ou infrastructures de taille équivalente, une capacité qui n'est pas aussi prononcée avec Pléiades-HR. Les résultats illustrent et confirment les avantages substantiels des données Pléiades Neo pour l'évaluation post-catastrophe, avec une précision accrue dans la détection et la caractérisation des dommages au bâti. L'importance de l'angle d'acquisition des images, mais également la complémentarité de Pléiades Neo par rapport à Pléiades-HR dans le contexte de la cartographie d'urgence, ont également été évoquées. Cette étude atteste des avantages des images Pléiades Neo par rapport à Pléiades-HR dans la gestion des dégâts au bâti suite à des événements catastrophiques.
Instruments and machines, Applied optics. Photonics
In this paper, an artificial general perfect magnetic conductor (PMC) decoupling structure is proposed to improve the isolation between two-element closely spaced antenna arrays with an operating frequency around 2.4 GHz. This kind of PMC structure can effectively activate the in-phase coupling current and cancel the antiphase coupling current raised by the original perfect electric conductor (PEC) equivalent interface, thereby blocking the energy coupling from one antenna input port to another. The proposed design is composed of a transmission line and a lumped element in the neutral position of a pair of electrically small antennas. To validate the utility of this approach, we analyze the current/field distribution of this structure and the mode superposition mechanism in the present paper. The results show that, with a close center-to-center distance of 5 mm, the isolation between the arrays is improved from −5 dB to −20 dB at around 2.4 GHz. Furthermore, to validate the feature that this special in-phase coupling current distribution is insensitive to frequency, we analyze the decoupling performance in a frequency reconfiguration or a dual-frequencytwo-element antenna array. The decoupling feature emerges in the proposed structure over a larger frequency range (2.2–2.6 GHz) than the previous design. A sample of this two-element frequency reconfiguration antenna system is fabricated and measured in this paper. We also realized a dual-frequency antenna system with expected isolation. Through the above discussion, we can know that these decoupling geometrical parameters can be worked in the whole range of 2.2–2.6 GHz with the same decoupling structural parameters. Good performance and compact structures make the proposed structure suitable for mobile communication applications.
A small-size 2×2 broadband circularly polarized microstrip antenna array is proposed in this article. The array has four broadband dual-feed U-slot patch antenna elements with circular polarization, and the sequential feeding technique is used to further enhance the 3 dB axial ratio bandwidth. The lateral size of the fabricated array is as small as 1.33λ0×1.33λ0, and the profile is only 0.04λ0. Measured results show that the overlapped −10 dB reflection coefficient and the 3 dB AR bandwidth is 53%, and the variation of the measured realized gain is less than 1 dB for S-band satellite communications (1.98–2.2 GHz).
Three-dimensional (3D) microwave imaging has been proven to be well suited for concealed weapon detection application. For the 3D image reconstruction under two-dimensional (2D) planar aperture condition, most of current imaging algorithms focus on decomposing the 3D free space Green function by exploiting the stationary phase and, consequently, the accuracy of the final imagery is obtained at a sacrifice of computational complexity due to the need of interpolation. In this paper, from an alternative viewpoint, we propose a novel interpolation-free imaging algorithm based on wavefront reconstruction theory. The algorithm is an extension of the 2D range stacking algorithm (RSA) with the advantages of low computational cost and high precision. The algorithm uses different reference signal spectrums at different range bins and then forms the target functions at desired range bin by a concise coherent summation. Several practical issues such as the propagation loss compensation, wavefront reconstruction, and aliasing mitigating are also considered. The sampling criterion and the achievable resolutions for the proposed algorithm are also derived. Finally, the proposed method is validated through extensive computer simulations and real-field experiments. The results show that accurate 3D image can be generated at a very high speed by utilizing the proposed algorithm.
Sounik Kiran Kumar Dash, Taimoor Khan, Binod Kumar Kanaujia
et al.
A wideband and high gain dielectric resonator antenna (DRA) operating in hybrid HEM11δ mode is proposed. The investigated geometry employs one cylindrical dielectric resonator partially covered with a transparent dielectric superstrate and backed up by a single side metal coated dielectric reflector plane. The reflector is dedicated for gain enhancement while the superstrate is employed for merging of two resonant bands resulting in a single wide band. The dielectric resonator is excited by simple microstrip feed slot coupling technique and operates over X-band, ranging from 7.12 GHz to 8.29 GHz, that is, of 15.18% impedance matching bandwidth with 11.34 dBi peak gain. The different development stages like standalone DRA, DRA with superstrate, DRA with reflector, and DRA with both superstrate and reflector plane with respect to bandwidth and gain performances are analyzed properly. To the best of authors’ knowledge, this is the first time this type of combination of both superstrate and reflector plane is demonstrated in DRA engineering. An antenna prototype was fabricated and characterized and a very good agreement is achieved between the simulated and measured results.
A wideband dual-polarized slot antenna loaded with artificial magnetic conductor (AMC) is proposed for WLAN/WIMAX and LTE applications. The slot antenna mainly consists of two pairs of arrow-shaped slots along the diagonals of the square patch. Stepped microstrip feedlines are placed orthogonally to excite the horizontal and vertical polarizations of the antenna. To realize unidirectional radiation and low profile, an AMC surface composed of 7 × 7 unit cells is designed underneath a distance of 0.09λ0 (λ0 being the wavelength in free space at 2.25 GHz) from the slot antenna. Both the dual-polarized slot antenna and the AMC surface are fabricated and measured. Experimental results demonstrate that the proposed antenna achieves for both polarizations a wide impedance bandwidth (return loss 10 dB) of 36.7%, operating from 1.96 to 2.84 GHz. The isolation between the two input ports keeps higher than 29 dB whereas the cross-polarization levels basically maintain lower than −30 dB across the entire frequency band. High front-to-back ratios better than 22 dB and a stable gain higher than 8 dBi are obtained over the whole band.
Erja Sipilä, Johanna Virkki, Lauri Sydänheimo
et al.
The integration of electronics and wood is an interesting research area due to the increasing interest to add functionality into various wooden products. The passive RFID-based humidity sensor tag prototype, presented in this paper, is fabricated directly on plywood substrate to be embedded into wooden structures, by using brush-painting and photonic sintering of cost-effective silver ink. To the best of our knowledge, this is the first demonstration of brush-painted antennas as sensor elements. The developed sensor tag is fully passive and small in size, meaning it can be permanently enclosed into wooden structures. In addition, the sensor tag has all the functionalities of an ordinary passive UHF RFID tag, and a peak read range of about 10 meters. The sensor performance was evaluated in normal room conditions, after two 100% relative humidity tests, and after drying in normal room conditions for 9 days. According to the results, the fabricated UHF RFID-based humidity sensor tags have a great potential to be utilized in humidity sensing applications, and also in normal automatic identification and supply chain control of various wooden products. In addition, the first results of more cost-effective brush-painted copper UHF RFID tags on plywood substrate are presented.
Reflector antennas have been widely used in many areas. In the implementation of parabolic reflector antenna for broadcasting satellite applications, it is essential for the spacecraft antenna to provide precise contoured beam to effectively serve the required region. For this purpose, combinations of more than one beam are required. Therefore, a tool utilizing ray tracing method is developed to calculate precise off-axis beams for multibeam antenna system. In the multibeam system, each beam will be fed from different feed positions to allow the main beam to be radiated at the exact direction on the coverage area. Thus, detailed study on caustics of a parabolic reflector antenna is performed and presented in this paper, which is to investigate the behaviour of the rays and its relation to various antenna parameters. In order to produce accurate data for the analysis, the caustic behaviours are investigated in two distinctive modes: scanning plane and transverse plane. This paper presents the detailed discussions on the derivation of the ray tracing algorithms, the establishment of the equations of caustic loci, and the verification of the method through calculation of radiation pattern.
Due to the polarization diversity (PD) of element patterns caused by the varying curvature of the conformal carrier, the conventional direction-of-arrival (DOA) estimation algorithms could not be applied to the conformal array. In order to describe the PD of conformal array, the polarization parameter is considered in the snapshot data model. The paramount difficulty for DOA estimation is the coupling between the angle information and polarization parameter. Based on the characteristic of the cylindrical conformal array, the decoupling between the polarization parameter and DOA can be realized with a specially designed array structure. 2D-DOA estimation of the cylindrical conformal array is accomplished via parallel factor analysis (PARAFAC) theory. To avoid parameter pairing problem, the algorithm forms a PARAFAC model of the covariance matrices in the covariance domain. The proposed algorithm can also be generalized to other conformal array structures and nonuniform noise scenario. Cramer-Rao bound (CRB) is derived and simulation results with the cylindrical conformal array are presented to verify the performance of the proposed algorithm.
High-frequency (HF) over-the-horizon radar (OTHR) works in a very complicated electromagnetic environment. It usually suffers performance degradation caused by transient interference. In this paper, we study the transient interference excision and full spectrum reconstruction of maneuvering targets. The segmental subspace projection (SP) approach is applied to suppress the clutter and locate the transient interference. After interference excision, the spectrum is reconstructed from incomplete measurements via compressive sensing (CS) by using a redundant Fourier-chirp dictionary. An improved orthogonal matching pursuit (IOMP) algorithm is developed to solve the sparse decomposition optimization. Experimental results demonstrate the effectiveness of the proposed methods.
This work investigates fade dynamics of satellite communication systems in equatorial heavy rain region based on a one year of Ku-band propagation measurement campaign carried out in Universiti Teknologi Malaysia (UTM), Johor, Malaysia. First order statistics of rain attenuation are deduced and the results are found to be in good agreement with those obtained from other beacon measurements gathered within the same area (Kuala Lumpur). Moreover, the fade duration and slope statistics of the satellite signal variations are also carefully derived and subsequently compared with the ITU-R recommendation model. Such information is useful for the system operator and radio communication engineer for the design of appropriate fade mitigation techniques as well as the quality of service that could be offered to the user (according to the time interval for a typical day). Further evaluation on the performances of several ITU-R models in the heavy rain region are needed based on the measurement database available of this climatic region.
Renato Cicchetti, Francesco D’Agostino, Flaminio Ferrara
et al.
An overview of the near-field-far-field (NF-FF) transformation techniques with innovative spiral scannings, useful to derive the radiation patterns of the antennas commonly employed in the modern wireless communication systems, is provided in this paper. The theoretical background and the development of a unified theory of the spiral scannings for quasi-spherical and nonspherical antennas are described, and an optimal sampling interpolation expansion to evaluate the probe response on a quite arbitrary rotational surface from a nonredundant number of its samples, collected along a proper spiral wrapping it, is presented. This unified theory can be applied to spirals wrapping the conventional scanning surfaces and makes it possible to accurately reconstruct the NF data required by the NF-FF transformation employing the corresponding classical scanning. A remarkable reduction of the measurement time is so achieved, due to the use of continuous and synchronized movements of the positioning systems and to the reduced number of needed NF measurements. Some numerical and experimental results relevant to the spherical spiral scanning case when dealing with quasi-planar and electrically long antennas are shown.
Reconfigurable bistate metasurfaces composed of interwoven spiral arrays with embedded pin diodes are proposed for single and dual polarisation operation. The switching capability is enabled by pin diodes that change the array response between transmission and reflection modes at the specified frequencies. The spiral conductors forming the metasurface also supply the dc bias for controlling pin diodes, thus avoiding the need of additional bias circuitry that can cause parasitic interference and affect the metasurface response. The simulation results show that proposed active metasurfaces exhibit good isolation between transmission and reflection states, while retaining excellent angular and polarisation stability with the large fractional bandwidth (FBW) inherent to the original passive arrays.
Chien-Sheng Chen, Chyuan-Der Lu, Ho-Nien Shou
et al.
Advances in wireless communications have enabled various technologies for wireless digital communication. In the field of digital radio broadcasting, several specifications have been proposed, such as Eureka-147 and digital radio mondiale (DRM). These systems require a new spectrum assignment, which incurs heavy cost due to the depletion of the available spectrum. Therefore, the in-band on-channel (IBOC) system has been developed to work in the same band with the conventional analog radio and to provide digital broadcasting services. This paper discusses the function and algorithm of the high definition (HD) radio frequency modulation (FM) digital radio broadcasting system. Content includes data format allocation, constellation mapping, orthogonal frequency division multiplexing (OFDM) modulation of the transmitter, timing synchronization, OFDM demodulation, integer and fraction carrier frequency (integer carrier frequency offset (ICFO) and fractional CFO (FCFO)) estimation, and channel estimation of the receiver. When we implement this system to the field programmable gate array (FPGA) based on a hardware platform, both theoretical and practical aspects have been considered to accommodate the available hardware resources.
At present, more and more electronic tags are used in Antitheft system; it is important to examine the performance of electronic tags. The traditional single-transmitter-coil antenna (STC antenna) of the electronic tags tester has some serious drawbacks. So a novel double-transmitter-coil antenna (DTC antenna) is presented in this paper. Compared to the traditional STC antenna, this new antenna has a more excellent performance in the tag test systems, especially when it is used for testing the quality factor of tags.