A broadband circularly polarized antenna array is proposed in this paper. The array consists of four sequentially rotated feed groove-backed strip antennas. Compact size (46 mm × 46 mm × 1.6 mm), wide impedance bandwidth (4.62-9.92 GHz), and wide 3 dB axial ratio bandwidth (4.48-8.52 GHz) can be observed. The measured peak gain is 7.5 dBi at 8.2 GHz, and good agreement between the simulated and measured results can be achieved.
A novel four-step weakly conditionally stable hybrid implicit-explicit finite-difference time-domain (HIE-FDTD) algorithm in three-dimensional (3-D) domains is presented in this paper, which is suitable for a finer discretization in one dimension. Based on the exponential evolution operator (EEO), the Maxwell's equations in a matrix form can be split into four sub-procedures. Accordingly, the time step is divided into four sub-steps. In addition, by taking second-order central finite-difference approximation for both the temporal and spatial derivatives, the formulation of the proposed four-step HIE-FDTD method is obtained. The proposed four-step HIE-FDTD algorithm is implemented, in which the implicit scheme was applied only in one direction with a fine grid, and the explicit scheme was applied in two other directions with coarser grids. Compared with the existing HIE-FDTD methods, the proposed method has a weaker Courant-Friedrichs-Lewy (CFL) stability condition (and), which means that the proposed method can improve computational efficiency by taking larger time step size. Since the CFLN stability condition of the proposed method is determined by the smaller grid size of the two coarse grid sizes, the proposed method is suitable for analyzing the electromagnetic objects with fine structures in one direction effectively. Besides, the numerical dispersion analysis is given, and the (Δt ≤ 2Δx/c and Δt ≤ 2Δz/c) comparisons of the numerical dispersion analysis among the proposed method, traditional FDTD method, ADI-FDTD method, and two existing HIE-FDTD methods are given. Finally, to testify the computational accuracy and efficiency, numerical experiments of the five FDTD methods are presented.
A wireless power transfer system is designed to power remotely placed wireless sensors using UHF band. For receiving purpose, a small and compact, bi-quad antenna isdesigned which has a fractional bandwidth of 6.89% (443.65 MHz-475.5 MHz). The receiver antenna is uni-directional and has the maximum gain of 9.7 dBi. The overall dimensions of the antenna including the reflective ground plane are 50 cm × 30 cm × 16 cm (0.767λ × 0.46λ × 0.172λ at 460 MHz). A General Mobile Radio Service (GMRS) radio license is obtained and a frequency of 462.55 MHz is used during the test measurement. The maximum achieved effective distance is 150 ft with 3.52 V, which is enough for powering most of the commercial sensors.
A two-dimensional (2D) band-gap wire structure with a spatial defect has been fabricated and studied in order to demonstrate which way the violation of periodicity affects its spectral properties. We experimentally demonstrate and numerically verify the occurrence of defect modes revealed as localized resonant peak inside the band gap transmission spectrum of 2D band-gap wire structure. We also demonstrate the efficient frequency tunability of these defect mode peaks by varying defect size in the frequency range 22-40 GHz. The visualization and analysis of spatial electromagnetic (EM) field distribution within the defect of 2D band-gap wire structure is performed both experimentally and numerically. A good agreement between the experiment and numerical simulation is demonstrated.
The paper presents the results of the use of iron nanotubes as the anode material of lithium-ion batteries. To assess the degradation of the morphology of nanostructures after different numbers of cycles of life tests, the method of scanning electron microscopy, Mossbauer spectroscopy, and X-ray diffraction analysis were applied. It is shown that the decrease in discharge capacity starts at the 380th cycle and is caused by the onset of degradation processes of nanostructures due to the formation of amorphous inclusions and an increase in macrostresses and distortions in the structure. The complete degradation of the structure is observed after the 492nd life cycle test. According to the data obtained by Mossbauer spectroscopy, it has been established that an increase in life cycles leads to an increase in contribution of partial spectrum characteristic of a paramagnetic state. That indicates an increase in degradation rate of nanostructures and an increase in the content of impurity inclusions and amorphous formations in the crystal structure.
Orbital angular momentum (OAM) as a powerful candidate to enhance the spectral efficiency and system capacity by providing the new degree of freedom for multiplexing has been recently advocated in wireless communications. In this paper, we propose an OAM-based massive multiple-input multiple-output (MIMO) scheme to significantly improve the transmission performance of wireless communication system in line-of-sight scene.The uniform rectangular arrays (URAs) are used as transceivers in our system model, and the ideal OAM antenna model that is capable of providing OAM-channel independently is used as the array element. Multiple reference coordinate systems based on per transmitting antenna and the cumulative phase of specific radio vortices are used to describe the OAM-MIMO channel model. The results of numerical analysis indicate that the proposed OAM-based massive MIMO system could obtain an overwhelming capacity gain against the conventional MIMO system.
In many modern GPR systems, it is desired to detect the presence of targets in the interference which includes clutter and noise. Detection of water leaks using GPR has been aimed in this work. Pipe and soil are known as the clutter of data in this scenario. Various signal processing techniques like multivariate subspace-based algorithms are proposed to effectively suppress the clutter and increase the signal to interference ratio. Combining Independent Component Analysis (ICA) and Principal Component Analysis (PCA) as a unique algorithm has demonstrated the ability to eliminate the GPR clutter and extract the target signal.
Electromagnetic (EM) vortex wave carrying orbital angular momentum (OAM) has attracted a lot of attention in radar imaging, due to its potential capability of new degree of freedom for information modulation. Most existing OAM-based radar imaging methods require abundant OAM modes to realize the azimuth resolution. Switching between the OAM modes frequently increases the burden of radar antenna and the complexity of beam steering. In this paper, a novel electromagnetic vortex synthetic aperture radar (EMV-SAR) model with equivalent squint imaging is established.The geometrical model and echo signal model are derived correspondingly. By analyzing the echo signal model, amplitude and phase modulation introduced by the OAM aect the azimuth focusing, and traditional imaging algorithms are no longer applicable. Hence, a novel image formation method based on the traditional Chirp-Scaling (CS) algorithm is proposed for the EMV-SAR. The amplitude weighting function and phase modulation function are derived accurately, and high-precision focusing processing is achieved by modied CS algorithm. Point targets simulation results validate that the image focusing performance can be improved signicantly using the proposed algorithm.
Aimed at the deficiency of conventional parameter-level methods in radar specific emitter identification (SEI), which heavily relies on empirical experience and cannot adapt to the waveform change, a novel algorithm is proposed to extract specific features and identify in Hilbert-Huang transform domain. Firstly, 2-dimensional physical representation of emitter is formed with Hilbert-Huang transform (HHT). Based on this, 4 types of multi-view features are constructed, and the feature space is spanned by elaborating the extraction. Principal components, between-class similarity, spectrum entropy, and deep architecture are used to describe the subtle features. Finally, support vector machine (SVM) is selected as the classifier to realize identification to alleviate the small sample problem. Experimental results show that the proposed algorithm realizes specific identification using 4 intentional modulations of simulated data. The selected 4 types of unintentional representations are feasible to discriminate identical emitters. Additionally, the proposed algorithm obtains higher accuracy than typical parameter-level methods in the signal-to-noise ratio (SNR) range [0, 20] dB.
In this paper, a localization algorithm for mixed near-field and far-field sources by an interlaced nested array is proposed. The fourth-order cumulants (FOCs) of the received data are used to construct a FOC matrix, by which the angles of all signals can be estimated. Then, an effective method is driven to separate the directions of arrival (DOAs) of near-field and far-field sources without extreme value search. The ranges of the near-field sources can be estimated by one-dimensional (1D) search. Compared with existing nested array-based algorithms, the proposed algorithm can distinguish more sources and has higher estimation accuracy. Some simulation results are shown to certify the superiority of proposed algorithm.
A miniaturized rectangle-shaped complementary split ring radiating element with an offset-fed microstrip line is reported for multiband operations. The fabricated antenna with a compact size of 19×19×1.6 mm3 is designed on an FR-4 substrate with loss tangent tanδ = 0.02 and dielectric constant (εr) of 4.4. Multiband and antenna miniaturization are achieved by a complementary split ring radiating element, and it produces an impedance bandwidth of 40 MHz resonance at 3.03 GHz, 40 MHz resonance at 3.66 GHz, and 1470 MHz resonance at 5.5 GHz. The passband behaviour of the complementary split ring radiating element is studied in detail for obtaining multiband abilities of the miniaturized antenna. The metamaterial property of the complementary split ring radiating element is analyzed, by which the negative permittivity (ε) existence and the new resonance frequency are confirmed. The fabricated antenna shows optimum performance at the measured radiation characteristics.
This work presents the novel design and development of a WC-281 circular waveguide terminator or termination for microwave plasma interaction experiments. Final waveguide terminator is designed by using the quad wedge of FR4, cone of resistive material Kanthal and Teflon discs. Kanthal is a composition of aluminium, chromium, and iron. Wedge shape geometry helps in gradually changing the impedance and thus decreasing the return loss, while resistive material Kanthal attenuates the field before reaching the receiving end. This makes it suitable for use as the finest microwave termination. Simulation is carried out by CST microwave studio. The final model of terminator decreases the reflection coefficient (S11) up to -40 dB while reduces the transmission coefficient (S21) immensely up to -63 dB at 2.85 GHz.
This paper amalgamates two uncorrelated techniques namely finite difference time domain technique (FDTD) and nonlinear autoregressive with exogenous input (NARX) neural network to achieve a faster computation of radar cross section (RCS). It generates only a limited number of FDTD data and uses them to train a NARX neural network. The data beyond this limited number for the FDTD come from the NARX prediction. Comparison of the performance of FDTD-NARX hybrid with other methods indicates good matching with better timing for RCS of electrically larger objects.
Plane wave diffraction by a finite number of metal cylindrical rectangular strips (patches) periodically placed on a dielectric rod (DR) surface in azimuth direction is considered. The problem is solved by the Method of Moments (MoM) in the spectral domain using PieceWise Sinusoidal (PWS) basis functions. Topologies with a highly resonant behavior of the patch currents in both azimuth and longitudinal directions are considered. This includes topologies with 1, 2, or 3 patches that are nearly touching, in which case one can also view the topology as a slotted metal cylinder. For these slotted cylinders with one and two slots it is shown that 2D approximate analytical solutions based on the rigorous Riemann-Hilbert approach yield a good agreement with 3D MoM solutions for the natural frequency of the half wavelength resonance until the slot width reaches 40˚. It is found that in the 3D case the natural frequency of the half-wavelength resonance for gap coupled patches tends to zero when the slot is vanishing. The radar cross-section versus frequency, resonant current distributions on the patches and far fields are presented.
This paper proposes an approach for estimating the spatial and polarization angles of mixed-targets in bistatic MIMO radar. Mixed-targets mean the combination of uncorrelated, partially correlated, and groups of coherent targets. The approach resolves rank deficiency of received signal covariance matrix and then exploits the ESPRIT-based method for estimating the angles of direction-of-departure (DOD) and direction-of-arrival (DOA). This paper also presents an analytical review and necessary conditions for resolving the rank deficiency under various scenarios of the MIMO radar. Simulation results show the effectiveness of the proposed approach.
Radio tomographic imaging (RTI) is a main method in device-free localization (DFL) that can locate a target by analyzing its shadowing effect on wireless links, while removing the requirement of equipping the target with a device. The accuracy of RTI method closely depends on the accuracy of shadowing weight model, which represents the relationship between the shadowing effect of the target on wireless links and target location. However, most existing models have not been accurate enough for many applications since they cannot explain some phenomena observed in DFL practices. To overcome the shortcoming of the existing weight model, this paper proposes a gradual-changing weight model to enhance the imaging quality of RTI. Meanwhile, a foreground target detection algorithm based on the shape feature of the target image is proposed to reduce the negative impact of background noises and pseudo-targets, thereby further enhancing the localization accuracy. The indoor and outdoor experimental results highlight the advantages of using the proposed method in improving the imaging quality and the positioning accuracy.
The negative refractive property of a meta-material medium modeled by an array of localized elements is demonstrated numerically using the iterative method based on the wave concept. This property is used to show the channeling and control of the electromagnetic beam inside the triangular shaped meta-material supports that are interfaced with the conventional positive refractive index supports. WCIP was used to view the electromagnetic behavior of a source placed in a right-hand medium interfaced with another left-hand medium in order to present the properties of the negative refraction.
Calculating the RCS (Radar Cross Section) of two 3D scatterers needs to numerically solve a set of integral equations involving numerous unknowns. Such a 3D problem can not be solved easily with a conventional Method of Moments (MoM) by using a direct LU inversion. Thus, a hybridization between the Extended Propagation-Inside-Layer Expansion (E-PILE) and the Physical Optics approximation (PO) reduces signicantly the memory requirements and CPU time. The resulting method called E-PILE+PO. In this work, we take advantage of the rank-decient nature of the coupling matrices, corresponding to scatterer 1 (the object) and scatterer 2 (the rough surface) interactions, to further reduce the complexity of the method by using the Adaptive Cross Approximation (ACA).
The plane wave diffraction by an acute-angled wedge located on a perfect electric conducting plane is studied in the frequency and time domains. Only a TMz polarization is explicitly considered in the manuscript since the case of a TEz polarization can be solved in a similar way. At first, the uniform asymptotic physical optics approach is used to obtain the diffraction coefficients in the framework of the uniform geometrical theory of diffraction. The analytical procedure allows one to obtain closed form expressions that are easy to handle and provide reliable results from the engineering viewpoint. The time domain diffraction coefficients are successively determined by applying the inverse Laplace transform to the frequency domain counterparts. The effectiveness of the proposed solutions is proved by means of numerical tests and comparisons with full-wave numerical techniques.
In this study, we propose a technique to improve the linearity of complementary metal-oxide semiconductor (CMOS) power amplifiers with a cascode structure. From the investigation of the influence of the impedance of an envelope signal on the linearity, we find that the load impedance of the envelope signal of the common-source transistor should be reduced. To obtain alow load impedance of the envelope signal, we reduce the value of the gate resistor of the common-gate transistor. After investigating the influences of the value of the resistance on the third-order intermodulation distortion (IMD3), we extract the optimum value of the resistance. We also consider the electrostatic discharge protection issue and the effects of the variations in the parasitic components of bond-wires, in the process of the extraction of the optimum value. To verify the feasibility of the optimization technique of the resistance ofthe bias circuit of the common-gate transistor of the amplifier, we design a power amplifier using a 180-nm RFCMOS process for wireless local area network (WLAN) 802.11n applications. We obtain the measured maximum linear output power of 22.2 dBm with a 26.7% power-added efficiency and a 3.72% error vector magnitude. We use an 802.11n modulated signal with 64-QAM (MCS7) at 65 Mb/s. From the measured results, we successfully verify the feasibility of the proposed optimization technique of the resistance of the bias circuit of the common-gate transistor.