Two-Dimensional Direction of Arrival (2D-DOA) estimation is increasingly important in recent years. In this paper, a new method is proposed to estimate the 2D-DOAs of multiple spatial sources using a three-parallel uniform linear array assuming that some of the sensors happen to be out-of-order. Firstly, a Matrix Completion (MC) algorithm is applied to recover the observed incomplete data, and then an improved joint azimuth and elevation angle estimation algorithm using the recovered data is proposed to obtain the correct parameter estimation. Finally, computer simulation results show that the proposed algorithm has a great performance improvement compared to those based on incomplete data in terms of Signal-to-Noise Ratio (SNR) and the sample rate of sensors.
A hybrid-polarity architecture, consisting of transmitting circular polarisation and receiving two orthogonal linear polarisation and also their relative phase, was used to calculate four Stokes parameters. Different parameters like Degree of Polarisation, Alpha angle, Entropy, Anisotropy, Radar vegetation Index and decompositions like Raney decomposition (m-δ), Freeman-2 and 3 component decompositions were derived from these hybrid data. Crop biophysical parameters viz. plant height, plant age and plant biomass of cotton crops grown under two different environments, i.e., rainfed and irrigated in Guajrat, India were studied with respect to derived polarimetric parameters. Right circular transmitted and horizontally (RH) and vertically (RV) received backscatter values show good relation with the plant height, age and biomass. RH backscatter -13 dB to -7 dB and RV backscatter from -13 to -10dB were observed for crop biophysical parameters. Volume component of all decomposition showed strong response to the increase in height, age and biomass of the plant. Radar Vegetation index (RVI) values have also shown significant increase from 0.6 to 0.7 with increasing age of the crop. The rate of growth was slow in the initial phase, but fast post mid-July for both early and late sown cases. The polarimetric parameters were found significantly correlated to the above plant biophysical parameters.
In this paper we compare current implementations of commonly used numerical techniques - the Finite-Difference Time-Domain (FDTD) method, the Finite-Integration Technique (FIT), and Time-Domain Integral Equations (TDIE) - to solve the canonical problem of a horizontal dipole antenna radiating over lossless and lossy half-spaces. These types of environment are important starting points for simulating many Ground Penetrating Radar (GPR applications which operate in the near-field of the antenna, where the interaction among the antenna, the ground, and targets is important. We analysed the simulated current at the centre of the dipole antenna, as well as the electric field at different distances from the centre of the antenna inside the half-space. We observed that the results from the simulations using the FDTD and FIT methods agreed well with each other in all of the environments. Comparisons of the electric field showed that the TDIE technique agreed with the FDTD and FIT methods when observation distances were towards the far-field of the antenna but degraded closer to the antenna. These results provide evidence necessary to develop a hybridisation of current implementations of the FDTD and TDIE methods to capitalise on the strengths of each technique.
A material sample of Camphour Sulphonic Acid doped Polyaniline (PANI-CSA) is contemplated towards its conceivable use as a microwave shield. Shielding towards electromagnetic interferences (EMI) is measured over various frequency bands by the waveguide method. Plane wave electromagnetic theory is used to generalize the overall reflection and transmission coefficients of the polymer. EMI shielding of the polymer, in the form of Shielding Efficiency (SE), is analyzed over the microwave frequency range from 2 to 18 GHz, demonstrating the potential value of the polymer as an electromagnetic interference (EMI) shield for commercial purposes. The shielding film is fabricated using standard procedure with CSA as the dopant and m-cresol as the solvent. The shielding effectiveness as high as 45 dB for the sample of PANI doped with CSA is observed.
A novel bearingless stirring permanent-magnet (PM) (BSPM) machine is proposed in this paper, which can offer high torque density, high efficiency, simple structure, and low cost. The novelty of the proposed machine is to provide a clean environment and no pinch-off areas in a stirred tank bioreactor and integrate appropriate magnetization directions of the PMs in the rotor. Firstly, the topology and operational principle of the proposed machine are described in detail. Then, the machine is designed for a given set of specifications, and its electromagnetic performances are analyzed by time-stepped transient finite-element method (FEM). Next, after the analysis of loss, a thermal simulation is established, complying with the design requirements. Finally, the efficiency and power factor map of the proposed BSPM machine are simulated for validation.
Microwave staring correlated imaging (MSCI) achieves high resolution imaging results by employing the temporal-spatial independent radiation field. In MSCI, the imaging performance is determined by the independent degree of the radiation field. In this paper, a novel kind of ideal independent radiation field named the orthogonal radiation field (ORF) is constructed for MSCI. Firstly, a group of two-dimensional (2-D) orthogonal basis functions are used to construct the ideal ORF samples. Then a method is proposed to construct the ORF samples by designing the transmitting signals. The numerical simulations validate the feasibility of this method. Finally, when the ORF is applied in MSCI, the numerical simulations achieve high resolution imaging results and demonstrate good imaging performance that is robust to noise.
An adaptive sharp boundary inversion scheme is developed to improve resolution with feasibility for transient electromagnetic (TEM) data inversion. By using weighted minimum gradient support (WMGS) constraint, this method focuses the resistivity change areas on layer boundary locations. Prior information describing roughness can be added into the constraint to improve resolution. Furthermore, even though no prior information about layer boundaries is available, it can still reconstruct models with geo-electrical interfaces. Synthetic models prove that this method has a better performance in presenting layer boundaries than smooth-model inversion. Field data of a TEM test line are inverted using this method, which makes the basement layer visualized easily.
A new architecture for a low profile miniaturized frequency selective surface based on complementary structure capable of providing a high angular stable performance is proposed. The proposed FSS is composed of an array of convoluted cross dipoles and its complementary slots pattern that is separated by a thin dielectric substrate. An equivalent circuit model for this FSS is presented to provide a deep insight into the mechanism of reducing the unit size by shifting and lengthening the dipoles. With the use of this method, the FSS unit cell size has been significantly reduced to only 0.0085λ×0.0085λ, and the thickness is 0.000093λ, where λ represents the resonant wavelength in free space. Moreover, the proposed FSS achieves good stability in the scope of incidence angles of 86 degrees for both TE and TM polarizations. Besides, the length of the dipoles can tune the resonant frequency.
A new method for calculating the time-domain (TD) transfer function of ultra-wide band (UWB) antennas, which is used for measuring the electromagnetic pulse (EMP) at VHF, is proposed. The phase of the complex antenna factor is constructed based on the Hilbert transform that describes the relationship between the phase and amplitude of a signal in frequency domain (FD). The detailed steps for calibrating the TD transfer function are discussed, and the calibration uncertainty, whose maximum value equals 2.79 dB, is estimated. The presented method is verified by TEM cell calibration, in which the TD transfer function of a wideband antenna is calculated and used to reconstruct time domain electromagnetic pulse. The results show that the difference between the calibrated result with TEM cell calibration and the reconstructed result is 0.58 dB.
In this paper, after a brief review of the previous nonlinear power amplifier (PA) classes including Class-B, Class-F, and Class-J, a novel design theory for high-efficiency and high-linearity microwave power amplifier based on 2nd harmonic component of the drain voltage and current signals is proposed. The new scheme introduces a new nonlinear class which like Class-J tunes only two primary harmonic components but unlike Class-J, the drain voltage is boosted to the maximum four times dc drain voltage. A quasi half sinusoidal waveform for the current and a quadratic sinusoidal waveform for the voltage are thus realized in this class, leading to a minimum waveform overlapping. The new class theoretically provides 93% power efficiency. It is, in fact, an enhanced Class-J with higher power efficiency and better linearity performance.
This article takes account of the radiation feature of rivers in synthetic aperture radar (SAR) images and proposes a novel automatic approach to detect highway bridges by combining statistical and topology features. The proposed method consists of two steps. In the river-extraction stage, the classification techniques are applied to water extraction according to the statistical and gray-leveled features. In the bridge-extraction stage, bridges are then detected in this binary image by using a topology-based approach. Experimental results show that the proposed method can be implemented with high-precision highway-bridge extraction, feature analysis, and bridge recognition.
We investigate thermal noise mechanisms and present analytical expressions of the noise power spectral density at high frequencies (HF) in Silicon-on-insulator (SOI) MOSFETs. The developed HF noise model of RF T-gate body contact (TB) SOI MOSFET for 0.13-μm SOI CMOS technology accounts for the mechanisms of 1) channel thermal noise; 2) induced gate noise; 3) substrate resistance noise and 4) gate resistance thermal noise. The extraction method of modeling parameter utilized by Y-parameter analysis on the proposed small-signal equivalent circuit is demonstrated in this paper. Excellent agreement between simulated and measured noise data is obtained at different temperatures.
Grounding grid is responsible for driving lightning and short circuit currents into ground. Faults in substation grounding grid can lead to significant rise in surface potential and ultimately loss to power system and operators. This paper proposes a novel technique based on derivative method to diagnose breakpoints in grounding grid. Derivative of surface magnetic flux density on circle results in peak at conductor's location. Once a conductor is broken the flow of current and surface magnetic field ceases, which is recognized by the absence of peak at corresponding conductor's location. The use of circle even enables this method for diagnosing diagonal branch. Furthermore, the method is analyzed for soil of different resistivities and monolayer and multilayer soils. Simulation results show that the proposed method is feasible for breakpoint diagnosis of grounding grid without excavation.
The modulational instability of a lower hybrid wave is investigated in a dusty plasma slab by developing a non-local theory of this four wave parametric interaction process. The immersed dust grains modify the dispersion relation and growth rate expression of low frequency unstable mode. A numerical analysis shows that the frequencies and growth rate of unstable mode is higher in dusty plasma than that in without dust grains. The growth rate of the unstable mode is proportional to pump amplitude and has strong dependence on pump frequency.
In this paper, radio wave propagation over irregular terrain is investigated in 200-600 MHz (VHF/UHF band). Measured results are compared with different path loss models such as Fresnel knife edge diffraction and uniform theory of diffraction (UTD). It is shown that, for low antenna heights, using a combination of the two-ray path loss model and knife-edge diffraction, great improvement in path loss prediction accuracy is achieved. The derived model is aimed to effectively predict path loss for near-ground and short-range communication applications.
DBS (Doppler Beam Sharpening) imaging for scene matching terminal guidance is investigated. An echo simulation method for DBS of missile-borne radar that considers environmental factors is presented. The transmission signals of missile-borne radar are studied first. Next, the method for the modeling of the echo signals is discussed with consideration of environmental influences including the objects on the ground, radome and the seasonal variations, especially undulation of the ground. The status of the surface of the earth as well as internal elements of the radar will influence the precision of the height measurement, thereby indirectly influencing the image matching. Undulating terrain can also cause changes in the electromagnetic characteristics that lie in the translation of image points; in addition, there is a close relationship between the position offset and the altitude of the image area. The operation flow of DBS is provided together with the method of generating reference images. Finally, an optical image of an airport and the simulation results using echoes are presented for validation.
The performance of a Concentric Circular Antenna Array (CCAA) with robust techniques is presented in this paper. A CCAA geometry is chosen because of its symmetrical configuration which enables the phased array antenna to scan azimuthally with minimal changes in its beam width and side-lobe levels. The performance of CCAA system is degraded, if there is any disparity occur between the original signal direction and the steering direction of the beamformer. This performance degradation problem due to look direction disparity can be improved by using robust techniques. This paper proposes a technique, named variable diagonal loading (VDL) technique for CCAA system and compare the performance of the proposed robust CCAA processor with existing CCAA processors. The proposed robust CCAA beamformer enhanced the output power 28.9 dB, 9.34 dB and 1.63 dB at 10 disparity angle compared to the CCAA standard capon beamformer (SCB), robust SCB and existing novel loading technique. Numerical examples are presented to analyze the performance of the proposed robust beamformer in different scenarios.
The measured raindrop size distribution (DSD) and the ITU-R model have been used to elucidate the regional and diurnal variations of rain attenuation in Indonesia, for Ku-band (13.6 GHz), Ka-band (35.6 GHz), and W-band (96 GHz) frequencies. The DSDs were measured by the Parsivel disdrometer at Kototabang (KT; 100.32˚E, 0.20˚S), Padang (PD; 100:21˚E, 0:57˚S), Pontianak (PT; 109:37˚E, 0:00˚S), Manado (MN; 124:92˚E, 1:55˚N) and Biak (BK; 136:10˚E, 1:18˚S). In general, PD, KT and PT have lower rain attenuation than those at MN and BK, for the same rainfall rate, due to lower concentration of small-sized drops at these sites as reported by a previous study. Considerable differences between the attenuation obtained from the DSD and the ITU-R model are observed at all locations, in particular for very heavy rainfall (R > 50 mm/h). For R < 50 mm/h, the specific rain attenuation of measured DSD is in fairly good agreement with that obtained from the ITU-R model. The specific rain attenuation obtained from the DSD shows diurnal variation, in agreement with a previous study at KT. The diurnal variation of rain attenuation is dependent on the frequency and rainfall rate. At KT and PT, the lowest rain attenuation for Ku-band is observed during 06:00-12:00 LT, but during this period the largest attenuation is observed for Ka- and W-bands. These phenomena may be due to the increasing role of small and medium-sized drops by increasing frequency.
In this work, the multi-resonance behavior of a suspended ring antenna structure with a single port has been investigated. Introduction of symmetrical slots at each arm of the ring structure enables quad-band operation. The antenna yields good impedance matching at 3.4 GHz, 4.5 GHz, 5.8 GHz and 7.5 GHz with considerably high gain response up to 6 dBi. Maintaining suitable air height from the ground plane enhances the bandwidth up to 12%. This compact antenna shows bandwidths of 130 MHz, 360 MHz, 850 MHz, and 380 MHz, respectively. Each resonance claims an efficient use in next generation wireless communication within S-band and C-band radio links extensively and also applicable in WSNs/IoTs which requires a multi-functional antenna system. Theoretical analysis of the proposed antenna is investigated with the equivalent lumped circuit. The antenna element is excited using separate feed patch alongside of the ring. The antenna exhibits TM10, TM01, TM11 excitation modes at different resonances. The said antenna is implemented on an FR4 substrate with dielectric constant of 4.4, substrate thickness of h = 1.56 mm and loss tangent of tanδ=0.02. The antenna is designed with physical dimensions of 18×18×7.56 mm3 which claims its compactness.
A new method of impedance synthesis of antenna array radiation fields based on a single methodological conception is presented. At first, an approximate solution for the current in the thin vibrator with variable impedance was obtained using the partial averaging operation of the integraldifferential equation. The variable impedance of the vibrator was taken into account in the form of an integral coefficient averaged along the vibrator length. The approach turns out to be common for radiators with impedance coatings of different configurations and (or) different distributions of lumped impedances. It is established that the shape of the vibrator radiation pattern (RP) does not depend on the form of the impedance distribution function, and it is determined only by the averaged value of the impedance distribution along the vibrator axis. The solution shows that the impedance coating of a symmetrical thin vibrator excited at the center by the voltage δ-generator affects the shape of the radiation pattern in the wave zone, and the effect is directly proportional to the small natural parameter of the problem. The synthesis problem of the radiator impedances for the spatial scanning of the RP was solved for the linear vibrator array. The analytical solution of the problem was obtained for the equidistant array of symmetric vibrators with equal excitation currents. The possibility of changing the RP shape over a wide range by varying the intrinsic complex impedances of the vibrators is demonstrated for an equidistant linear array consisting of 5 half-wave vibrators located at a distance of one eighth wavelength from each other in the free space.