In this paper, a new radar constant false alarm rate detector to perform adaptive threshold target detection in presence of interfering targets is proposed. The proposed CFAR detector, referred to as Adaptive Linear Combined CFAR, ALC-CFAR, employs an adaptive composite approach based on the well-known cell averaging CFAR, CA-CFAR, and the ordered statistics, OS-CFAR, detectors. Data in the reference window is used to compute an adaptive weighting factor employed in the fusion scheme. Based on this factor, the ALC-CFAR tailors the background estimation algorithm. The conducted Monte Carlo simulation results demonstrate that the proposed detector provides low loss CFAR performance in an homogeneous environment and also performs robustly in presence of interfering targets. The performances of the ALC-CFAR detector have been evaluated and compared with that of the CA-CFAR and the OS-CFAR detectors. The obtained results are presented and discussed in this paper.
A study of the raindrop size distribution along the eastern coast of South Africa (Durban) is presented. The Biweight kernel estimator based on distometer measurement is used to determine the best estimate of the measured raindrop size probability distribution function (pdf). The best kernel estimator, which results in the lowest integral square error (ISE), is used to measure the closeness of the estimated lognormal and gamma pdf of raindrop size to the measured raindrop size distribution. It is established that the optimised lognormal pdf slightly outperforms the optimised gamma pdf in terms of the mean ISE and the RMSE values, with mean ISE values of 0.026 for lognormal and 0.04 for gamma distributions, respectively, and corresponding mean RMSE values of 0.073 and 0.081, respectively. The method-of-moments gamma and lognormal distributions are observed to be worse estimators of the measured pdf than the two optimized distributions. The N(D) distributions using the optimised l gnormal and gamma distributions for the region are compared with those for different tropical regions, namely, India, Singapore, Nigeria, Indonesia, and Brazil. While the Indian lognormal N(D) model gives the highest peak for low raindrop sizes for all rain rates, Durban's gamma and lognormal models exhibit the widest raindrop size spread over all rain rates ranging from 1-120 mm/h. Finally, the specific attenuation due to rain using the Durban models are compared against the ITU-R models and actual measurements over a 19.5 GHz LOS link; the results indicate a need for further work involving both distrometer and radio link measurements for rain rates exceeding 30 mm/h in the eastern coast of South Africa.
A numerically efficient approach for the rigorous computation of bi-static scattering and radiation problems is presented. The approach is based on an improvement of a previous method scheme that combines the Characteristic Basis Function Method (CBFM) and the Multilevel Fast Multipole Algorithm (MLFMA). The approach combines Characteristic Basis Functions (CBFS) and subdomains functions for reducing the CPU time in the pre-process and in the solving iterative process for simple or multiple excitations. It is intended for use in very large cases where an iterative solution process cannot be avoided, even considering the matrix size reduction achieved by the CBFM. This reduction is particularly important for solving radiation or bistatic problems in which an integral equation is solved once.
In this paper, we consider the problem of bistatic multiple-input multiple-output (MIMO) radar systems design for parameters estimation. Maximum channel capacity is used as criterion for the problem of optimal systems design under transmitted power constraint and channel constraint. We obtain that the system design based on maximum channel capacity can be expressed as a joint optimization problem. Given the number of transmit antenna, the number of receive antenna and signal-noise ratio (SNR), the maximum channel capacity can be determined. This maximum channel capacity can be obtained from a unique appropriate power allocation and antenna placement strategy, which is very important for system design.
The propagation equation, written in a curvilinear coordinate system, is solved by using a perturbation method inspired from quantum physics and extended to imaginary eigenvalues and evanescent waves. The parameter of perturbation is the groove depth which is small compared to the period. The method is expanded up to second order for the non-degenerate problem. In this way the solutions have analytical form compared to a numerical method. They present the advantage to put in evidence the evolution of the energy distribution for different diffraction orders as a function of the magnitude of the perturbation. The efficiencies which are deduced from these analytical solutions are compared of those obtained by the curvilinear coordinate method. The good agreement between the two methods occurs for a groove depth with respect to the wavelength less than or equal to 0.16. Thus, this new approach opens a new range of applications for inverse problems.
This paper presents a development of a wideband delta-sigma modulator for fully digital GHz transmitters. The fully digital RF transmitter is developed as a promising solution for software defined radio (SDR) terminals and applications. The fully digital transmitter consists of a delta-sigma modulator, a high-speed multiplexer and a switching-mode power amplifier. The speed limitation of delta-sigma modulator is the main limitation to increase the signal bandwidth in fully digital transmitters. In this paper, the bandwidth of the fully digital transmitter is increased 8 times using parallel processing time-interleaved architecture, while maintaining the same signal quality. This architecture was implemented on FPGA and tested for different standards (WiMAX and LTE) with a signal bandwidth up to 8 MHz. The concept was assessed in terms of SNDR by using a differential logic analyzer at the output of FPGA, and the SNDR was found to be around 60 dB.
In this paper, a new kind of printed TEM horn antenna with high-gain fed by balanced microstrip line is proposed. The radiation part of the antenna (printed on the FR4 epoxy substrate) is composed of two symmetrical triangular metal foil branches fed by balanced microstrip line. The antenna has been simulated by CST MICROWAVE STUDIO® software, and the simulated results show that the proposed antenna is a kind of traveling wave antenna. Besides, an equivalent adopted V-shaped antenna model is proposed to describe the radiation characteristic of the antenna. The simulated and measured results indicate that in the frequency range from 1.64 GHz to 9 GHz, the reflection coefficient of the antenna is less than -6 dB, and in the work frequency band, the average gain value is over 8.2 dB. The antenna gain will be improved greatly by extending the length of the dielectric slab appropriately (in the main radiation direction) without influencing the bandwidth. The measured and simulated results have a good consistency. This antenna will have wide application in the UWB field.
The adaptive sliding-mode observer has been widely used to estimate the rotor flux and rotor speed in inverter-fed sensorless induction motor drives. However, the technique requires setting a priori the sliding-mode observer constants and also knowledge of the induction motor parameters. This particular aspect can cause significant errors in the estimation of the rotor speed used in sensorless control schemes. Changes in the induction machine parameters due to temperature or different saturation levels will affect the dynamic operation of the observer despite its adaptive nature. In this context, a sensitivity study of the adaptive sliding-mode observer is presented and discussed in this paper. Various experiments are performed on a sensorless indirect vector-controlled induction motor drive under a variety of conditions to verify the observer robustness.
In this paper, we propose the design of high sensitivity and selectivity metamaterial-based biosensors operating in the THz regime. The proposed sensors consist of planar array of resonant metallic structures, whose frequency response is modified through the variation of the surrounding dielectric environment. We consider different resonator geometries, such as the squared, circular, asymmetrical, and omega ones, and the analysis of the biosensors is conducted through proper equivalent quasi-static analytical circuit models. The metallic particles are assumed deposited on a glass substrate through proper titanium adhesion layers. Exploiting the proposed analytical model, which is verified through the comparison to full-wave numerical simulations, we study the biosensor resonance frequencies as a function of the geometric parameters of the individual inclusions. Finally, we optimize the structure in order to obtain high sensitivity and selectivity performances. The numerical results show that the proposed structures can be successfully applied as biosensors working in the THz region.
Based on quasi-static electromagnetic field theory, recently grounding system under alternative currents (AC) substation has been studied with equal potential and unequal potential models. In these numerical models, the closed form of Green's function for a point source within a horizontal multilayered earth model and its quasi-static complex image method have been fully discussed. However, less information about how to achieve the closed form of Green's function through Matrix Pencil method is presented in these references. In this paper, we discuss how the kernel of the Green's function can be expanded into a finite exponential series.
Rain attenuation is an important aspect of signal propagation above 10 GHz frequency. The attenuation time series generation from point rain rate measurement is crucial due to unavailability of actual signal measurements. In this paper, a simple and realistic approach has been demonstrated for better estimation of rain attenuation using Ku-band signal propagation data and ground rain rate measurements at Kolkata, India. The ITU-R model of rain attenuation has been modified by incorporating an effective slant path model. The effective slant path has been estimated and modelled in terms of a power-law relationship of rain rate data of 2007-2008. The methodology has been validated with the measured data of 2006. Comparison with ITU-R and SAM clearly demonstrates the improved predictability of the proposed model at the present tropical location.
Microwave Imaging is one of the most promising emerging imaging technologies for breast cancer detection, and exploits the dielectric contrast between normal and malignant breast tissue at microwave frequencies. The development of many UWB Radar imaging approaches requires the use of accurate numerical models for the propagation and scattering of microwave signals within the breast. The Finite-Difference Time-Domain (FDTD) method is the most commonly used numerical modelling technique used to model the propagation of Electromagnetic (EM) waves in biological tissue. However, it is critical that an FDTD model accurately represents the dielectric properties of the constituent tissues, including tumour tissues, and the highly correlated distribution of these tissues within the breast. This paper presents a comprehensive review of the latest findings regarding dielectric properties of normal and cancerous breast tissue, and the heterogeneity of normal breast tissue. Furthermore, existing FDTD models of the breast described in the literature are examined.
The rigorous uncertainty estimation in Electromagnetic Compatibility (EMC) testing is a complex task that has been addressed through a simplified approach that typically assumes that all the contributions are uncorrelated and symmetric, and combine them in a linear or linearized model using the error propagation law. These assumptions may affect the reliability of test results, and therefore, it is advisable to use alternative methods, such as Monte Carlo Method (MCM), for the calculation and validation of measurement uncertainty. This paper presents the results of the estimation of uncertainty for some of the most common EMC tests, such as: the measurement of radiated and conducted emissions according to CISPR 22 and radiated (IEC 61000-4-3) and conducted (IEC 61000-4-6) immunity, using both the conventional techniques of the Guide to the Expression of Uncertainty in Measurement (GUM) and the Monte Carlo Method. The results show no significant differences between the uncertainty estimated using the aforementioned methods, and it was observed that the GUM uncertainty framework slightly overestimates the overall uncertainty for the cases evaluated here. Although the GUM Uncertainty Framework proves to be adequate for the particular EMC tests that were considered, generally the Monte Carlo Method has features that avoid the assumptions and the limitations of the GUM Uncertainty Framework.
This paper presents a rigorous approach for the propagation of electromagnetic (EM) fields along a helical waveguide with slab and rectangular dielectric profiles in the rectangular cross section. The main objective is to develop a numerical method for the calculation of the output fields, for an arbitrary step's angle and the radius of the cylinder of the helical waveguide. The other objectives are to present the technique to calculate the dielectric profiles and their transverse derivatives in the cross-section and to demonstrate the ability of the model to solve practical problems with slab and rectangular dielectric profiles in the rectangular cross section of the helical waveguide. The method is based on Fourier coefficients of the transverse dielectric profile and those of the input wave profile. Laplace transform is necessary to obtain the comfortable and simple input-output connections of the fields. This model is useful for the analysis of helical waveguides with slab and rectangular dielectric profiles in the metallic helical waveguides in the microwave and the millimeter-wave regimes. The output power transmission and the output power density are improved by increasing the step's angle or the radius of the cylinder of the helical waveguide, especially in the cases of space curved waveguides.
In this article, a coplanar inverted-F antenna with an electronically controlled ground slot enabling reconfigurability is proposed. Initially a quarter wavelength coplanar inverted-F radiator is designed to operate at 900 MHz. To minimize its size, the radiator is folded to occupy an area of about 10 × 40 mm2. Next, a ground slot is introduced to excite another resonance at around 1850 MHz without affecting the 900 MHz operation. The slot is loaded with three pairs of PIN diode switches with simple biasing circuits to vary its resonant frequency. The proposed reconfigurable antenna is fabricated and experimentally tested. A good agreement is achieved between the simulated and measured return loss of the antenna showing the experimental impedance bandwidth covering GSM900, PCS1900 and UMTS2100 services. In these frequency bands, the antenna offers nearly omni-directional radiation patterns with measured peak gain between 1.4 dBi to 3.45 dBi.
The number of children suffering from heat-related illness has been increasing in recent years. Children are more susceptible to heat-related illness than adults, which is considered to be caused by morphological and functional differences between adults and children. In the present study, the temperature change and perspiration in adult and child models during a simultaneous exposure to solar radiation and a hot environment are evaluated computationally. First, the power absorbed in the human body due to solar radiation is computed by the FDTD method for the Maxwell equations. Then, the temperature distribution inside the human body is modeled by the bioheat equation taking into account the thermophysiological response. Anatomically-based Japanese adult male and 3-year-old child phantoms are used. An approximative analytical solution for the core temperature elevation is also derived to clarify the dominant factors affecting the temperature elevation. From our computational results, the core temperature elevation in the child phantom for both the solar and hot-environment exposures was larger than that in the adult phantom. The temperature elevation in the child was found to be mainly caused by the exposure to a hot environmental temperature while that in the adult was due to the environmental heat and solar radiation almost equally. This difference was mainly attributed to the difference in the surface area-to-mass ratio between the adult and child phantoms. This finding was confirmed by comparison with an approximative analytical solution.
Tadpole-shaped (Ni, Al)/AlN nanoparticles were synthesized via evaporating Ni-Al alloy in a mixed atmosphere of N2 and H2. As a counterpart, the spherical-shaped (Ni, Al)/Al2O3 The electromagnetic parameters of as-made nanoparticles/paraffin composites were then investigated in the frequency range of 2-18 GHz. Excellent microwave absorption can be obtained for the tadpole-shaped (Ni, Al)/AlN-paraffin composite at high frequencies and in a thin layer, which is thought to be the result of the enhanced polarization in the anisotropic tadpole-shaped nanoparticles. With the increasing of the composite thickness, the frequency of effective reflection loss shifts towards lower frequencies due to an improved impedance match and absorption.
In this paper, a novel and computationally efficient algorithm which combines Array Signal Processing (ASP) approach with Fourier Optics (FO) is developed in the realm of gain enhancement achieved by placing Uniplanar Compact-Photonic Band Gap (UC-PBG) structures on top of microstrip antennas. The proposed scheme applies FO to the well-known sampling theorem borrowed from Digital Signal Processing (DSP) analysis in the framework of ASP approach which we refer to as the FDA algorithm. The FDA algorithm is suitable for lossless UC-PBG structures with 1-D, 2-D and 3-D lattice of canonical geometrical apertures, such as circular, octagonal, hexagonal, and square. In order to validate the proposed approach, two different UC-PBG structures of octagonal and circular apertures are considered at 2.6 GHz. The UC-PBG structures under consideration consist of two layers positioned above a microstrip antenna; each layer is an array of 9×9 apertures separated by half of the focal length distance of the lens in the near-field of the microstrip antenna. The performance of the microstrip antenna with and without the UC-PBG is reported using numerical simulations performed using CST Microwave Studio (CST MWS) based on the Finite Integration Technique (FIT). The radiation patterns and directivity of the microstrip antenna based on UC-PBG structures are evaluated using the proposed FDA algorithm and validated against numerical results obtained from CST MWS where an excellent agreement is found between the FDA algorithm and the 3-D full wave simulations. The UC-PBG structure of octagonal apertures provides a remarkable enhancement in the bore-sight gain of about 7.8 dBi at 2.6 GHz with respect to that obtained from the conventional microstrip antenna, while the circular apertures provide gain enhancement in excess of 10 dBi above the gain of the same microstrip antenna.
A coherent imaging system images a frame or an object onto a changing diffuser and projects the resulting pattern which generally contains speckles. Using a spatial light modulator (SLM) as the changing diffuser, the speckles in the pattern are suppressed without the need for any other mechanisms. With $M$ random phasor arrays being displayed in the SLM during the integration time of a detector, a suppression factor (Cf) of speckles, 1/√M, is achievable in the projected pattern, which is the sum of the intensity of M uncorrelated patterns. This paper shows both theoretically and in simulations that the Cf of the sum pattern was considerably reduced when two elementary patterns with fully developed speckles were negatively correlated. With the correlation coefficients of the elementary patterns found at [-0.3, -0.25], the Cf of the sum of 10 negatively-correlated speckle patterns was 48% lower than the Cf of the sum of 10\,uncorrelated speckle patterns. The negatively correlated patterns can be implemented using spatial light modulators or diffractive optical elements, and are used to suppress speckle noise in digital holography, laser projection display, and holographic display projections with relatively high efficiency.
A new type of elevated coplanar waveguide structure is described which uses airbridge technology to suspend CPW traces above a ground plane resting on a high permittivity substrate. The transmission line is effectively shielded from the substrate and is equivalent to conductor backed CPW with an extremely thin, air substrate. It is, therefore, insensitive to parasitic substrate effects such as surface waves and the effect of dielectric loss tangent. In comparison with other forms of CPW with typical lateral dimensions, the structure exhibits no high frequency roll-off at frequencies of around 240 GHz and above. Measured results show 2.5 dB/mm insertion loss at 320 GHz for a 51 Ω line. In order to demonstrate the performance of the new line at mm-wave frequencies, several passive components have been fabricated, measured and their performance compared with CPW counterparts. The experimental results, which are in close agreement with simulation results, for short and open circuited matching stubs, and band-pass and band-stop filters, clearly show improvements in terms of loss and in the characteristics of the frequency response. Also, in order to make some qualitative assessment of the variation in performance with elevation, results for elevations of 6 μm and 13 μm are compared. Low loss and a simple, MMIC compatible, fabrication process make grounded elevated CPW a promising transmission media for MMIC applications at the very high end of the millimeter-wave frequency spectrum.