This paper describes the use of the correlation maps in the Ground Penetrating Radar (GPR) for the detection of near surface objects. This method is based on the definition of bi-dimensional maps that describe the level and the nature of coherence between the received electromagnetic signals. The technique proposed provides the detection of objects, reducing the impact of the clutter and improving the image contrast by an appropriate combination of the information collected in the variance and time coherence of the received signals. The method has been tested in GPR developed by ourselves and described in detail. The implemented GPR system features a high dynamic vector network analyzer (VNA) and a mechanically scanned Vivaldi antenna; the scanning is bi-dimensional, so that A, B and C scans are available.
The motivation behind fusing multimodality, multiresolution images is to create a single image with improved interpretability. In this paper, we propose a novel multimodality Medical Image Fusion (MIF) method, based on Ripplet Transform Type-I (RT) for spatially registered, multi-sensor, multi-resolution medical images. RT is a new Multi-scale Geometric Analysis (MGA) tool, capable of resolving two dimensional (2D) singularities and representing image edges more efficiently. The source medical images are first transformed by discrete RT (DRT). Different fusion rules are applied to the different subbands of the transformed images. Then inverse DRT (IDRT) is applied to the fused coefficients to get the fused image. The performance of the proposed scheme is evaluated by various quantitative measures like Mutual Information (MI), Spatial Frequency (SF), and Entropy (EN) etc. Visual and quantitative analysis shows, that the proposed technique performs better compared to fusion scheme based on Contourlet Transform (CNT).
In this paper we analyze the dependence of the resonance wavelength and mode formation of an optical gold nanorod antenna on its geometrical parameters in the wavelength range 500-1400 nm. In particular, we prove that nanoantennas differ from RF counterparts, since the minima and maxima, i.e., nodes and anti-nodes, of the resonant modes do not go to zero and show very intense peak at the corners due to non-negligible thickness. Moreover, FDTD simulations reveal that the usually considered linear relation between the resonant wavelength and the nanorod length has to be modified when the nanorod thickness is taken into account.
The mutual conversion of the TMmn and TEmn waves (m, n ≠ 0) in periodic and aperiodic (fractal-like) stratified waveguide structures composed of dense metal-strip gratings is studied. The stopbands and passbands conditions of Bloch waves, the reflection and transmission spectra of the periodic structure are examined versus the gratings parameters. Peculiarities of the wave localization, selfsimilarity and scalability of both reflected and transmitted spectra of the fractal-like structure are investigated. The appearance of additional peak multiplets in stopbands is revealed and a correlation of their properties with the parameter of grating filling is established.
In this paper, we have proposed a shell type dielectric microsphere resonator in order to enhance its quality factor. In this work we have assumed that the radius of dielectric microsphere is 12 μm and that the interior metal layer radius is 11.5 μm. We have obtained analytic equations for Vector potentials, characteristic equation, quality factor, resonance frequency and resonance location of TE modes. We have plotted these characteristics by MATLAB software and compared them with the normal microsphere characteristics.
The feasibility of designing a compact-size beam-switching dielectric lens antenna (DLA) with improved angular (scanning) characteristics is investigated numerically using inhouse software based on the Muller boundary integral equations and hybrid genetic algorithm. It is demonstrated that joint optimization of the lens shape and feeding array parameters enables one to minimize the directivity degradation for off-axis feeds which is a well-known drawback of conventional extended hemielliptic DLAs fed by focal arrays. The key to success is found in proper shaping the lens profile and using arrays of non-identical feeds.
This paper presents the design, development and experimental characterization of a monolithic phased array antenna integrated on a microwave laminate. A four-element linear antenna array is realized by cofabricating the corporate feed network, microstrip-CPW transitions, DC blocks, and mesoscale phase shifters on the same substrate. The phase shifters used here are electrostatically actuated and their operation is similar to that of the distributed MEMS transmission line phase shifters. Various components of the array are designed and are individually evaluated before fabricating together. The measured radiation pattern characteristics for this array shows a scan angle of 10° in the X-band. All fabrication processes employed here can be performed at a good printed circuit manufacturing facility. This simple approach of cofabricating various components can be readily extended for large phased arrays required in radar and space communication applications.
Phase-retrieval from measured phaseless field data is of interest for various applications including electromagnetic dosimetry, electromagnetic compatibility investigations, near-field to far-field transformations and antenna diagnostics. In this study two phaseretrieval methods are compared. The first method, the adjoint field method, employs a gradient-based optimization algorithm based on the adjoint fields. The second method, the phase angle gradient method, uses an optimization algorithm based on the phase angle gradients of a functional. The methods are tested with numerical test cases and the phase angle gradient method is found to retrieve the phase with the best accuracy. Moreover it gives results that agree well with correct phase.
An equivalent circuit, made of the chain connection of a number of T-type twoport networks, is proposed for the very accurate representation of the frequency-domain behavior of radially inhomogeneous solitary cylindrical structures, the individual two-port networks being made of frequency-independent R, L and C lumped elements. The accuracy of the model is dictated by the number of two-port networks, a number that increases with the frequency. The equivalent circuit approach is validated with the help of an application example concerning a special type of inhomogeneous tubular structures where exact closedform field solutions do exist.
The diurnal and seasonal variation of surface refractivity over Nigeria was studied using four years in-situ meteorological data from eight location over Nigeria. At all the stations studied, it was observed that the diurnal refractivity variation was caused majorly by the dry term in the rainy season and the wet term is the major cause of refractivity variation in dry season except Sokoto and Jos. In Sokoto the result was found to be opposite and it is attributed to the fact that in dry season the humidity is almost close to zero while in rainy season the pressure seems to be almost constant but the temperature fluctuates rapidly and consequently the humidity. The variation pattern in Jos is as observed because of the altitude (~1000 m above sea level). At this altitude pressure variation seems to be insignificant. The result also show that the surface refractivity generally have higher value during rainy season than dry season at all location studied. The result also show that the value of surface refractivity increases from arid region in the north to the coastal area in south. The result also show that the diurnal refractivity variation is basically a function of local meteorology and while seasonal variation is caused follows the climatic condition.
With recent advances in both algorithm and component technologies, through-the-wall sensing and imaging is emerging as an affordable sensor technology in civilian and military settings. One of the primary objectives of through-the-wall radar imaging (TWRI) systems is to detect and identify targets of interest, such as humans and cache of weapons, enclosed in building structures. Effective approaches that achieve proper target radar cross section (RCS) registration behind walls must exploit a detailed understanding of the radar phenomenology, in general, and more specifically, knowledge of the expected strength of the radar return from targets of interest. In this paper, we investigate the effects of various wall types on the received power of the target return through the use of a combined measurement and electromagnetic modeling approach. The RCS of material-exact rifle and human models are investigated in free-space using numerical electromagnetic modeling tools. A modified radar range equation, which analytically accounts for the wall effects, including multiple reflections within a given homogeneous or layered wall, is then employed in conjunction with wideband measured parameters of various common wall types, to estimate the received power versus frequency from numerically modeled aforementioned targets of interest. The proposed technique is, in principle, applicable to both bistatic and monostatic operations. The results for various wall types, including drywall, brick, solid concrete and cinder block, under both wet and dry conditions, are presented.
This paper proposes a new approach for efficiently determining the unwanted interfering samples in the reference window, for the ordered statistics constant false alarm rate detector, based on the application of the information theoretic criteria principle. The proposed processor termed as Forward Automatic Order Selection Ordered Statistics Detector (FAOSOSD) does not require any prior information about the number of interfering targets. The proposed design aims to improve the Ordered Statistics Constant False Alarm Rate detector performance under severe interference situations. The number of interfering targets is obtained by minimizing the information theoretic criteria. Simulation results that illustrate the performance of the proposed method versus the classical OS-CFAR, the AND-CFAR and the OR-CFAR detectors are presented and discussed.
In this paper, a novel approach has been suggested to obtain an improved spurious-free window for dielectric resonator in microwave integrated circuit environment. In microwave integrated circuit environment, the dielectric resonator placed on a thin dielectric substrate gets located asymmetrically with respect to its shielding enclosure. A reduced separation in frequencies (mode separation) is one of a consequence of this asymmetry that may become a cause of spurious modes. This adverse influence of asymmetry is sought to be compensated by proposing a multi-layer multi-permittivity dielectric resonator structure with several layers of differing permittivity. The suggested approach takes advantage of the fact that the mode separation of a dielectric resonator configuration can be correlated to relevant resonance mode fields. By perturbing the resonance mode fields through the suggested multi-layer multi-permittivity approach, the adverse influence of asymmetry is found to reduce considerably over a comparative conventional ring dielectric resonator in microwave integrated circuit configuration. Still more improvement in mode separation are shown when the shape of the multi-layer multi-permittivity ring dielectric resonator is further modified, suggesting a scope for optimization in present approach.
Bistatic multiple-input multiple-output (MIMO) radar can improve the system performance for obtaining the waveform diversity and larger degrees of freedom (DoF), and effectively counteract the stealthy target for its transmit antennas and receive antennas separated placement. Similarly with the conventional bistatic radar, the geometry configurations of bistatic MIMO radar also play an important role in radar system's performance. Aimed at considering these effects of geometry configurations on the performance for bistatic MIMO radar, in this paper the extended ambiguity function is defined as the coherent cumulation of the matching output of all channels, where the information of the system geometry configuration is included in the received signal model. This new ambiguity function can be used to characterize the local and global resolution properties of the whole radar systems instead of only considering transmitted waveforms in Woodward's. In addition, some examples with the varying system configurations or target parameters are given to illustrate their effects, where the spatial stepped-frequency signal set (a quasi-orthogonal waveform set) is used. The simulation results demonstrate that the more approaching to monostatic MIMO radar case, the better ambiguity properties of time-delay and Doppler for bistatic MIMO radar.
In this paper, we propose a novel H-infinity filter based particle filter (H∞PF), which incorporates the H-infinity filter (H∞F) algorithm into the particle filter (PF). The basic idea of the H∞PF is that new particles are sampled by the H∞F algorithm. Since the H∞F algorithm can fully take into account the current measurements, when the new algorithm calculates the proposed probability density distribution, the sampling particles can take advantage of the system current measurements to predict the system state. The particles distribution we obtained approaches nearer to the state posterior probability distribution and the H∞PF alleviates the sample degeneracy problem which is common in the PF, especially when the maneuvers of the target tracking are large. Furthermore, the H∞F algorithm can adjust gain imbalance factor by adjusting disturbance decay factor, from that the new algorithm can get the compromise between the accuracy and robustness and we can obtain satisfied accuracy and robustness. Some simulations and experimental results show that the proposed particle filter performed better than the PF and the Kalman particle filter (KPF) in tracking maneuvering target.
In this paper, we propose a 3D model to characterize the field scattered by an urban area, which is composed of a group of buildings, for both monostatic and bistatic radar configurations. This model is based on a ray-tracing technique combined with the Uniform Theory of Diffraction (UTD). It is useful not only in elucidating mechanisms of ray propagation through the observed area, but also in evaluating the amplitude and the phase of any point in the far-zone scattered field above the ground. In order to validate the model, some comparisons with the commercial software XGTD R are presented. In addition, our model is tested against 33-37 GHz indoor measurements conducted in the anechoic chamber of the "ElectroMagnetic Effects Research Lab" (EMERL) in Singapore. These latter comparisons have shown that the model can predict precisely the location of a target placed between two metallic plates representing walls.
It is well-known that the stepped-frequency chirp signal (SFCS) technique is one of the very effective approaches for achieving high range resolution in radar [1-5]. The SFCS is a train of subchirp pulses with up-stepped or down-stepped carrier frequencies. However, there exists a rang-Doppler coupling problem (RDCP) when applying this signal to practical radar system because longer time is needed for transmitting a complete burst compared with that needed for transmitting just a single chirp. In radar system design, if carrier frequency step (△f) can be larger than the bandwidth of subchirp (Bm), it will be very helpful for using less number of subchirps to obtain high resolution and at the same time the influence of RDCP on imaging quality can be reduced. However the spectrum of transmitted signal is not continuous but with bandwidth gaps existing when Δf > Bm, and it will finally lead to high grating lobes in range profile. In this paper, the Super-SVA technique is applied to radar signal processing to solve the grating lobe problem arisen from bandwidth gaps. Super-SVA has been proven to be a very effective method used for extrapolating signal spectrum. Simulation and experiment results for moving train imaging are presented to show that the algorithm works very well.
The intent of this paper is to explore the application of information obtained from fully polarimetric data for land cover classification. Various land cover classification techniques are available in the literature, but still uncertainty exists in labeling various clusters to its own class without using any a priori information. Therefore, the present work is focused on analyzing useful intrinsic information extracted from SAR observables obtained by various decomposition techniques. The eigenvalue decomposition and Pauli decomposition have been carried out to separate classes on the basis of their scattering mechanisms. The various supervised classification techniques were applied in order to see possible differences among SAR observables in terms of information that they contain and their usefulness in classifying particular land cover type. Another important issue is labeling the clusters, and this work is carried out by decision tree classification that uses knowledge based approach. This classifier is implemented by scrupulous knowledge of data obtained by empirical evidence and their experimental validation. It has been demonstrated quantitatively that standard polarimetric parameters such as polarized backscatter coefficients (linear, circular and linear 45°), co and cross-pol ratios for both linear and circular polarizations can be used as information bearing features for making decision boundaries. This forms the basis of discrimination between various classes in sequential format. The classification approach has been evaluated for fully polarimetric ALOS PALSAR L-band level 1.1 data. The classifier uses these data to classify individual pixel into one of the five categories: water, tall vegetation, short vegetation, urban and bare soil surface. The quantitative results shown by this classifier gives classification accuracy of about 88%, which is better than other classification techniques (supervised classification techniques based on SAR observables).
The dyadic Green's functions (DGFs) for unbounded and layered general anisotropic media are considered in this paper. First, the DGF for unbounded problem is derived using the eigen-decomposition method. Two different approaches are proposed to obtain the DGF for layered problem when the source is located inside the anisotropic region. The first approach is to apply the modified symmetrical property of DGF to obtain the DGF for the field in the isotropic region when the source is located inside the anisotropic region, from the DGF for the field in anisotropic region when the source is in the isotropic region. This modified symmetrical property can be applied for the layered geometry with bounded anisotropic region being either reciprocal or non-reciprocal medium. However, this method can not give the DGF for the field inside the anisotropic region. Thus, the second approach is presented to obtain the complete set of DGFs for all the regions including the anisotropic region, by applying the direct construction method through eigen-decomposition together with matrix method.
In this paper we analyze the electromagnetic response of a metamaterial slab in the case of normal incidence using the point-dipole interaction model and an expansion of polarization by eigenmodes. The problem is simplified by assuming that the lattice dimensions are smaller than a half wavelength and invoking the nearest neighbor approximation. In this manner, we find the structure supports three modes: an ordinary mode and two extraordinary modes. In the long-wavelength limit, the ordinary mode propagates with the same wave number as that predicted using the classic Clausius-Mossotti relations, while, for most cases, the two extraordinary modes are confined to thin surface transition layers near the boundaries of the slab. A systematic method is presented to find the scattering from the slab, and the results are confirmed by full wave simulation using Ansoft HFSS.