A polarimetric radar system measures the complete scattering matrix of a target in the backscattered field that includes magnitudes of linearly polarized scattering amplitudes and the co-polarised and cross-polarised phase angles. Apart from backscattering intensity, the co-polarization phase difference (CPD) calculated from polarimetric synthetic aperture radar (SAR) data produces important information about target physical, geometrical and dielectric properties. In the present work, the distribution of CPD in C-band polarimetric SAR data corresponding to major kharif and rabi crops (denoting the monsoon and the winter season) and other land cover features have been studied over Central State Farm, Hisar, Haryana. The probability density functions (PDF) of CPD have been compared with dominant scattering contributions from these targets as obtained from polarimetric target decompositions. The results show that crops and other land cover features show characteristic CPD distributions, which relates well with crop physical and geometrical properties. An intuition of the rate of growth and plant vigour is indicative from the temporal PDF pattern.
In this paper, a simulation of ground penetrating radar ``GPR'' system on lossy and dispersive soil is investigated. The capability of the GPR system to detect buried targets is examined by evaluating and comparing the electromagnetic coupling between the transmitting and receiving antennas in two cases: (i) when the system is placed over an empty ground and(ii) when it is placed over a ground inside which a practical target is buried at a proper depth. Simulation software based on the finite difference time domain ``XFDTD'' is used for the electromagnetic simulations. The results concerning the coupling between the transmitting and receiving antennas are presented considering various practical parameters such as the operating frequency, the electric properties of the ground soil and the buried target, and the location at which the receiving element is placed. It is shown that the target detectability is strongly dependent on all of the above parameters. Also, the capability of target shape extraction and recognition are demonstrated through polarimetric ground penetrating radar.
Azimuthal Surface Waves (ASWs) are electromagnetic waves of the surface type, which propagate across an external steady magnetic field in plasma filled metal waveguides. The interaction between extraordinary ASWs and an electron beam that rotates along Larmor orbits in the gap between the plasma column and the metal wall is studied here. The initial stage of the ASW excitation is studied analytically and numerically. Growth rates of the ASW beam instability are analyzed as functions of the parameters of the plasma filled waveguide immersed in a steady magnetic field with toroidal nonuniformity. This nonuniformity leads also to the appearance of corrections to the ASW eigen frequencies. It is shown that the beam-wave interaction in a toroidally nonuniform steady magnetic field is not weaker than in the case of a uniform magnetic field. However, in the studied case, the efficiency of the power transfer from the beam into the excited waves becomes restricted due to the electron drift in the nonuniform magnetic field.
In this paper, frequency-tunable microstrip antennas, for cognitive radio applications, are proposed. The approach is based on electrically tuning the antenna's operating frequency by integrating reconfigurable band pass filters into wideband antenna structures. The design of an open loop resonator (OLR)-based bandstop filter, and its transformation to a bandpass filter, are investigated first. Then, the incorporation of the bandpass filter, with a wideband antenna, is detailed. The same methodology is employed to design cognitive radio pattern and polarization diversity tunable filter-antennas. A good agreement between the simulated and measured results for the different fabricated prototypes is attained.
In this paper, we derive a new geometrical blind corner scattering model for vehicle-to-infrastructure (V2I) communications. The proposed model takes into account single-bounce and double-bounce scattering stemming from fixed scatterers located on both sides of a curved street. Starting from the geometrical blind corner model, the exact expression of the angle of departure (AOD) is derived. Based on this expression, the probability density function (PDF) of the AOD and the Doppler power spectrum are determined. Analytical expressions for the channel gain and the temporal autocorrelation function (ACF) are provided under non-line-of-sight (NLOS) conditions. Additionally, we investigate the impact of the position of transmitting vehicle relatively to the receiving road-side unit on the channel statistics. Moreover, we study the performance of different digital modulations over a sum of singly and doubly scattered (SSDS) channel. Note that the proposed V2I channel model falls under the umbrella of SSDS channels since the transmitted signal undergoes a combination of single-bounce and double-bounce scattering. We study some characteristic quantities of SSDS channels and derive expressions for the average symbol error probability of several modulation schemes over SSDS channels with and without diversity combining. The validity of these analytical expressions is confirmed by computer-based simulations.
A new thin electromagnetic soft surface of strips in which ledge edges are used to reduce the strip period width and in turns a miniaturized structure is achieved. The designed surface is tested to reduce the mutual coupling between microstrip patches separated by a half wavelength. A 20% relative bandwidth of the bandgap is achieved. Study of the effect of different parameters is presented. The measurements show good agreement with the computed results.
In this paper, two novel vector sensors using a reduced number of radiating elements are proposed to estimate the directions of arrival of incoming electromagnetic signals in the 3D space, azimuth and elevation angles. The first one uses co-located radiating elements while the other one is based on distributed antenna elements. These two sensors combine only two half-loops and one linear monopole placed on a metallic plate in view of embedded applications. Full wave electromagnetic simulations are performed to take into account the electromagnetic coupling effects between the antenna elements. The directions of arrival estimation accuracy of electromagnetic signals incoming in arbitrary directions in the full 3D space are computed from the MUSIC algorithm. For experimental validation purpose, a prototype is manufactured and the directions of arrival measurements are performed. Then a novel vector sensor design with a reduced number of antenna elements is presented. The antenna elements are spatially distributed. An analysis is carried out to determine the largest distance between the antenna elements without causing ambiguous estimations in the 3D space . The estimation accuracy of the resulting sensor is reported. Finally the performances of these two vector sensors are compared.
Local Area Augmentation System (LAAS) is expected to enable the pilots to guide the aircraft more precisely and safely into busy airports even in poor visibility conditions. The anomalous low and equatorial latitude Ionosphere is severe threat to the LAAS system. To characterize the anomalous ionospheric gradients, the performance of an ionospheric threat model is evaluated. In our investigation, in contrast to the reported work available in the open literature, smoothed code phase measurements are used in the threat model to obtain precise ionospheric time delay. The three key parameters of the threat model gradient slope (mm/km), width (km) and front speed (m/s) are used in the analysis. Further, geometry screening using Maximum Ionosphere Induced Error in Vertical (MIEV) as a key parameter is carried out to identify the stationary gradients and its impact on system performance for CAT-I operations. A maximum ionospheric gradient of 355.74 mm/km over a distance of approximately 75 km is reported at mid latitudes. Whereas, in our findings at low/equatorial latitudes even within a distance of approximately 4 km a maximum gradient of 460 mm/km is observed, which is comparatively very high. Our results show that, there is necessity to enhance upper bound for the ionospheric gradients threat space over low latitudes.
We propose a theoretical study on the electromagnetic wave scattering from layered structures with an arbitrary number of rough interfaces by using the small perturbation method and the small slope approximation. The interfaces are characterized by Gaussian height distributions with zero mean values and Gaussian correlation functions. They can be correlated or not. The electromagnetic field in each medium is represented by a Rayleigh expansion and a perturbation method is used for solving the boundary value problem and determining the first-order scattering amplitudes by recurrence relations. The scattering amplitude under the first-order small slope approximation are deduced from results derived from the first-order small perturbation method. Comparison between these two analytical models and a numerical method based on the combination of scattering matrices is presented.
Structural, vibrational and microwave dielectric properties of Nickel-Copper-Zinc ferrite (Ni0.2CuxZn0.8-xFe2O4) ceramics have been presented in this paper. Samples have been prepared using conventional auto-combustion method. The X-ray diffraction (XRD) results confirmed the ferrite samples to be of cubic spinel structure, which further was validated by Fourier transform infrared (FT-IR) and Raman spectroscopy. The relative permittivity (εr) increased from 7.474 to 8.132 with successive increase in Cu content. The observed and calculated permittivity using Clausius-Mossoitti relation have been in good agreement. The temperature coefficient of resonant frequency (τf) decreased from -75.85 ppm/°C to -32.12 ppm/°C with increase in successive Cu content. The relative permeability (μr) have been calculated by using the Nicholson-Ross-Weir conversion technique. Using Ni0.2Cu0.2Zn0.6Fe2O4 sample the ferrite resonator antennas have been designed in three different shapes. The experimental and theoretical characteristics of the antennas have been compared and a good agreement has been achieved.
Recently, a novel approach for PN code acquisition of direct sequence code division multiple-access (DS-CDMA) systems in Rayleigh fading multipath channel was proposed in . The authors considered a combination of adaptive thresholding constant false alarm rate (CFAR) and smart antennas to increase the system capacity and consequently enhance the detection performance. This paper considers still the problem of PN code acquisition for DS-CDMA communication systems over Rayleigh fading channels under the presence of multipath and multiple-access interference (MAI) signals. We propose and analyze an adaptive array acquisition system, which integrates an adaptive thresholding technique based on ordered data variability (ODV) index constant false alarm rate (ODVCFAR) and digital beamforming where a low complexity least mean square (LMS) algorithm is used to calculate the optimal weighting coefficients. This approach is expected to mitigate interferences caused by the presence of multiple access interference and multipath. Unlike other approaches based on a fixed censoring point when the number of interferences is assumed known, ODV-CFAR processing does not require prior knowledge about the number of interferences. The simulation results show a robust performance of the proposed system in varying mobile communication channels.
In this study, a quad-band folded slot antenna with a monopole feed line embedded in a conductive housing structure (the LCD bracket of a mobile phone) is proposed. The performance of the proposed antenna is evaluated through simulation and measurement, demonstrating that it can provide total radiation efficiencies of more than 40% in the EGSM900, DCS, PCS, and WCDMA1 bands. Over these four bands, the total radiated power (TRP) of a prototype mobile phone using the antenna is 28.5, 27.1, 27.5, and 21 dBm, respectively, while the total isotropic sensitivity (TIS) is 102.7, 104.3, 103.8, and 107.3 dBm, respectively; all of these values satisfy Cellular Telecommunication and Internet Association (CTIA) requirements for over-the-area-(OTA) testing standards. The radiation performance of the proposed antenna in the calling mode is tested and shown to be within satisfactory limits; similarly, the specific absorption rates (SARs) of the prototype mobile phone are also found to be within standard SAR limits.
Ultra Wideband Radar imaging has shown promising results in the detection of small tumours within low to medium density human breasts. A wide range of beamforming algorithms has been presented in several recent studies with good tumour localization capabilities, but most of these suffer a deterioration in performance with an increase in breast tissue density. In this paper, a preprocessing filter is used to compensate for path-dependent attenuation and phase effects, in conjunction with a range of existing data-dependent and data-independent confocal microwave imaging algorithms. Results indicate that this data preprocessing improves the performance of all beamformers, enabling detection and accurate localization of multiple tumours in mild to moderately dense human breasts. The proposed framework is tested on 3D anatomically accurate numerical breast models and the performance is evaluated across a range of appropriate metrics.
Numerical computation of induced surface current density, power gain, conversion efficiency, optimum interaction length and harmonic generation etc. pertaining to large-signal operation of a linear beam travelling wave tube amplifier (TWTA) employing a dielectric-loaded sheath helix model for the slow-wave structure based on the large-signal theory developed in Part 1 of this paper is presented, and comparison with the results of other large-signal theories and available experimental evidence is made.
A rigorous field-theoretic method of analyzing the large-signal behavior of a linear beam traveling wave tube amplifier (TWTA) with slow-wave structure modeled to be a dielectric-loaded sheath helix is presented. The key step in the analysis is a representation of the field components as nonlinear functionals of the electron arrival time through a Green's function sequence for the slow-wave circuit. Substitution of this functional representation for the axial electric field component into the electron ballistic equation casts the latter into a fixed point format for a nonlinear operator in an appropriate function space. The fixed point, and therefore the solution for the electron-arrival time and hence the solution for the electromagnetic field components, can be obtained by standard successive approximation techniques. The calculations of the gain, the efficiency and the other amplifier parameters, comparison of the results of the present theory with experimental results etc., on the basis of such a successive approximation solution for the field components, will be presented in the second part of this paper.
Investigation on dielectric frequency selective structure with arbitrary shaped grating is done numerically for filter applications. To obtain well designed parameters, the effects of shape, size and dielectric constant of the structure are carefully studied. We examine in detail various structures and their spectral response which have not been reported by other authors. It is also shown how the frequency selective behavior of the structure can be controlled to meet a specific purpose for narrow linewidth filtering for normal incident angle. Results obtained for the scattering of several dielectric frequency selective surfaces are compared with both theoretical and experimental results presented in the literature, showing very good agreement. The effect of arbitrary angle of incidence is also shown to excite higher-order Floquet modes that affect the filtering properties.
Since the characters of poor inherent resolution and low signal-to-noise limit the application of the passive millimeter wave (PMMW) image, it is particularly important to improve the resolution and denoise the PMMW image. In this paper, the adaptive manifolds filtering algorithm based on non-local means (AM-NLM) is illustrated in detail. And an improved version of AM-NLM filtering algorithm is proposed for processing the PMMW image. The proposed algorithm firstly applies the AM-NLM filtering to obtain the basic denoised PMMW image. Then the image enhancement based on Laplacian of Gaussian operator is performed to enhance the edge of the target in PMMW image. Finally, the hard-threshold filtering with different thresholds is adopted to filter each dimension to achieve the final filtering response. Experimental results have shown that the proposed PMMW filtering algorithm has better and more satisfactory performance compared to AM-NLM, both in subjective visual effect and objective image quality metric. Additionally, our proposed algorithm is also available for real PMMW images.
A mathematical model for accurately computing, when combined with the Fast Fourier Transform (FFT), the lightning currents flowing along a high voltage a.c. substation's grounding system buried in half infinite homogenous earth has been developedn in this paper. It is a hybrid of Galerkin's method of moment and the conventional nodal analysis method. The model can calculate the distribution of both branch and leakage currents along the grounding system. The dynamic state complex image method and the closed form of Green's function of a dipole or monopole in the half infinite homogenous earth model are introduced into this model to accelerate the calculation of the mutual impedance and induction coefficients. Analytical formulae for the mutual induction and impedance coefficients have been developed to accelerate the calculation for near field case by Maclaurin expansion. With the inverse FFT, the model can be used to study the transient lightning response of a grounding system.
This paper deals with planar scanning technique of electromagnetic (EM) near-field (NF) emitted by electronic printed circuit boards (PCBs) fully in the time-domain (TD). The proposed EM scanning metrology is essentially based on the NF test bench available at the IRSEEM laboratory. It comprises motorized mechanical structures for moving the probe interconnected to electronic measurement instruments and controlled by a driver PC. The synoptic of the test bench is presented and technically examined. The characteristics of different elements constituting the measurement chain of the TD test bench understudy are described. The NF metrology developed is originally focused on the measurement of time-dependent magnetic field H(t) dedicated to the radiated emission electromagnetic compatibility (EMC) applications. An innovative calibration technique of the loop probe for detecting H(t) is established in order to ensure the post processing and extraction of the measured NF data. Then, validations were carried out via comparison with different simulations run with standard commercial tools. Mathematical analyses were also conducted for the improvement of the measurement post processing. To realize the mapping of time-dependent EM field components, a software interface edited with the graphical language LabVIEW was emulated to synchronize the probe displacement and the data acquisition. An UWB amplifier with average gain about 30 dB from DC to 300 MHz was designed and fabricated in order to decrease the measurement noise and to improve the quality of measured signals. As results of the study, TD NF mapping is demonstrated successfully by measuring the EM radiation emitted by electronic planar circuits. The technique developed is extremely useful in the field of EMC engineering for predicting the transient perturbations susceptible to degrade electronic functions in complex systems encountered usually for the automotive and aeronautic applications.
Due to the sensitivity of the field distribution within a resonant cavity to the presence of an object, conventional measurement techniques employing a probe suffer from a limited accuracy. Therefore we propose a new measurement technique of the electric field distribution that avoids the use of a probe. Based on the perturbation theory, it consists of a measure of the cavity resonant frequency variation while displacing a small perturbing object within the cavity. The choice of the perturbing object shape, dimension and material is discussed with the help of simulation and measurement results in a canonical case. The case of reverberation chamber equipped with a mode stirrer is also considered, as well as the insertion of a metallic box within the cavity. Our measurement setup is very low-cost, simple to set up and to use, and adapted to any cavity geometry.