Recent trends in propagation modeling indicate the study of mobile radio propagation modeling with the help of electromagnetic formulations which traditionally has been explained with empirical methods. These empirical methods were preferred by the cellular operators in their radio planning tools due to their ease of implementation and less time consumption. In the present study, AWAS electromagnetic code and conventional prediction methods have been employed to explain the observed results of ten base stations mainly in the near field zones of GSM 900 MHz band situated in the urban and suburban regions around Delhi in India. The suitability of the above models in terms of prediction errors and standard deviations are presented. Path loss exponents deduced from the observed data have been explained by Sommerfeld's formulations. Recent trends indicate the study of mobile radio propagation modeling with the help of electromagnetic formulations which traditionally has been explained with empirical methods. These empirical methods were preferred by the cellular operators in their radio planning tools due to their ease of implementation and less time consumption. In the present study AWAS electromagnetic code and conventional prediction methods have been employed to explain the observed results of ten base stations mainly in the near field zones of GSM 900 MHz band situated in the urban and suburban regions around Delhi in India. The suitability of the above models in terms of prediction errors and standard deviations are presented. Path loss exponents deduced from the observed data have been explained by Sommerfeld's formulations.
The transmission and reflection of electromagnetic waves at dielectric-fractal interface is studied, the fractal exhibits quasi fractional space properties.~The closed form expressions for transmission and reflection coefficients are formulated for such an interface. The classical results are obtained when integer dimensions, instead of fractional dimension are inserted in the said expressions. This work can be used to study behavior of electromagnetic waves in slabs and waveguides filled with fractal media.
High-resolution wide-swath (HRWS) imaging with spaceborne synthetic aperture radar (SAR) can be achieved by using azimuth displacement phase center antenna (DPCA) technique. However, it will consequently leads to extremely high data rate on satellite downlink system. A novel sparse sampling scheme based on compressed sensing (CS) theory for azimuth DPCA SAR was proposed, by which only a small proportion of radar echoes are utilized for imaging to reduce data rate. The corresponding image formation algorithm for the proposed scheme was presented in the paper. The SAR echo signal of each channel can be reconstructed with high probability by using orthogonal matching pursuit (OMP) algorithm in Doppler frequency domain. The reconstructed echo signals of each channel are jointly processed by means of spectrum reconstructing filter for compensating Doppler spectrum aliasing resulting from non-uniform sampling in azimuth direction. The high quality SAR image can be obtained by using chirp scaling algorithm. The effectiveness of the proposed approach was validated by computer simulations using both point targets and distributed targets.
A GHz Transverse Electromagnetic (GTEM) cell is proposed to investigate the arising of biological effects due to electromagnetic signals at the typical frequencies of mobile phone communications. The proposed GTEM cell, placed within a commercial incubator, has been ad hoc designed and fabricated to expose in vitro samples. The electromagnetic and the thermal analyses of the GTEM cell are reported. In particular, the inner electromagnetic field and the Specific Absorption Rate of the exposed sample (saline solution having 9 g/l concentration) have been evaluated by a home-made computer code based on the transmission line matrix method. Furthermore, the thermal analysis of the exposure arrangement has been carried out by the finite difference time domain algorithm.
A highly compact bandpass filter (BPF) is designed with a capacitively-coupled compact ring resonator. The ground plane is perturbed with a combination of two inter-digital and two spiral defected ground structures (DGSs), which enhance the selectivity and suppress the higher order harmonics of the BPF respectively. The filter has a selectivity of 0.22 dB/MHz, passband insertion loss (IL) of 1.55 dB and bandwidth of 61 MHz at 2.53 GHz. The proposed compact ring resonator yields a size reduction of 70.5% compared to a conventional ring resonator. This BPF is significant for wireless telemetry monitoring systems for physiological parameters including electrocardiogram (ECG), electroencephalography (EEG) and electromyography (EMG) using portable devices.
In this paper, a fully automatic goal-oriented hp-adaptive finite element strategy for open region electromagnetic problems (radiation and scattering) is presented. The methodology leads to exponential rates of convergence in terms of an upper bound of an user-prescribed quantity of interest. Thus, the adaptivity may be guided to provide an optimal error, not globally for the field in the whole finite element domain, but for specific parameters of engineering interest. For instance, the error on the numerical computation of the S-parameters of an antenna array, the field radiated by an antenna, or the Radar Cross Section on given directions, can be minimized. The efficiency of the approach is illustrated with several numerical simulations with two dimensional problem domains. Results include the comparison with the previously developed energy-norm based hp-adaptivity.
With the advancement of technology, the need of antenna arrays with shaped power patterns increases day by day for the purpose of improvement of communication. In this article, we represent a new method for designing optimized linear array with shaped beam radiation pattern of desired specifications. The main objective is to obtain suitable current excitation amplitude and phase distribution for the linear array elements so that it can produce the desired custom shaped radiation pattern as the user demands. The design procedure utilizes an improved variant of a prominent and efficient metaheuristics of current interest, namely the Differential Evolution (DE). In our modified DE algorithm, denoted as DE_rBM_2SX, new mutation and crossover strategies are employed. These modifications help to overcome some drawbacks of classical DE. Two examples of linear array with shaped radiation pattern design problem are considered to illustrate the effectiveness of our algorithm. Our results are also compared with two state-of-the-art variants of DE and Particle Swarm Optimization (PSO) - namely JADE and CLPSO (Comprehensive Learning Particle Swarm Optimization). The comparison clearly reveals that our optimization algorithm is more efficient than JADE or CLPSO in finding optimum element excitation amplitude and phase distribution for the desired shaped pattern.
We propose a 3D-approach of the soil surface height variations, either for the roughness characterization by the mean of the bidimensional correlation function, or as input of a backscattering model. We consider plots of 50\,cm by 50\,cm and two states of roughness of seedbed surfaces: an initial state just after tillage and a second state corresponding to the soil roughness evolution under a rainfall event. We show from stereovision data that the studied surfaces can be modelled as isotropic Gaussian processes. We study the change of roughness parameters between the two states. To discuss the relevance of their differences, we find from Monte-Carlo simulations the bias and variance of estimator for each roughness parameters. We study the roughness and moisture combined influences upon the direct backscattering coefficients by means of an exact method based on Maxwell's equations written in a nonorthogonal coordinate system and by averaging the scattering amplitudes over several realizations. We discuss results taking into account the numerical errors and the precision of radar. We show that the ability of the radar to discriminate the different states of seedbed surfaces is clearly linked to its precision.
The design and full-wave analysis of piezoelectric micro-needle antenna sensors for minimally invasive near-field detection of cancer-related anomalies of the skin is presented. To this end, an accurate locally conformal finite-difference time-domain procedure is adopted. In this way, an insightful understanding of the physical processes affecting the characteristics of the considered class of devices is achieved. This is important to improve the structure reliability, so optimizing the design cycle. In this regard, a suitable sensor layout is described, and discussed in detail. The major benefit of the proposed system stems from the potential for obtaining a superior performance in terms of input impedance matching and efficiency, in combination with an electronically tunable steering property of the near-field radiation intensity which can be profitably used to enhance the illumination and, hence, the localization of possible malignant lesions in the host medium. By using the detailed modeling approach, an extensive parametric study is carried out to analyze the effect produced on the sensor response by variations of the complex permittivity of the skin due to the presence of anomalous cells, and thus useful heuristic discrimination formulas for the evaluation of the exposure level to cancer risk are derived.
In this work, threshold mode structures of two-dimensional (2D) photonic crystal (PC) lasers are presented. The subjects of this paper are finite photonic crystal structures with circular holes arranged in square and triangular lattices. In each case, both transverse magnetic (TM) and transverse electric (TE) polarization are studied. The analysis is based on the coupled-wave equations and analyzes modes' behavior for the wide range of coupling coefficient values. The laser mode is characterized by threshold gain and frequency deviation, and these quantities depend on coupling constants, which means that the threshold gain of the mode and the mode's frequency deviation depend on the coupling constants. Presented analysis gives an interesting insight into behavior of the modes in photonic crystal lasers.
A simple traffic surveillance system based on the extraction of features from range-Doppler radar images is addressed. The concept exploits the High-Resolution Radars (HRR) properties. Specifically, a procedure is proposed to obtain some features from the HRR non-cooperative targets to enable their classification. These features are the distance, radial velocity, radial longitudinal dimension of the target, its integrated range-Doppler image based on a group of range-Doppler frames from each target, and both the coherent and non-coherent integrated range profiles. Experimental results from real scenarios using a high-resolution Linear-Frequency-Modulated Continuous-Wave (LFMCW) millimetre-wave radar are shown.
This paper presents the estimation of emissivity of calibration load using discretized scattering simulation data in bistatic reflection measurement, and analyzes the effect of several measured parameters on emissivity of calibration load. In the analysis of the impact of measured parameters on emissivity, a new calibration target is designed to improve the accuracy of emissivity measurement. In this bistatic measurement, the scattering from calibration load is simulated by FDTD (Finite-Difference Time-Domain) method. Based on Kirchhoff's law, the emissivity of calibration load is estimated by the discretized scattering data composed of different scanning angle interval and sampling azimuth planes. By the studies of simulation results, the estimation accuracy of emissivity of calibration load can be improved by selected appropriate measured parameters in bistatic reflection measurement.
In this paper, the applications of shunt open stubs are reported based on asymmetric half-wavelength resonators structure. To demonstrate the design ideas, the analysis methods of ABCD matrix and equivalent circuit are used. The multi-band bandpass, miniaturization and harmonic suppression by application of the shunt open stubs are demonstrated. The measured insertion loss of the dual-band filter with the center frequency of 1.9 and 5.8 GHz is less than 2.7 dB. The insertion loss of the tri-band filter with the center frequency of 1.5, 4 and 6.3 GHz is less than 2.7 dB. Furthermore, a compact bandpass filter with size around 12.3 mm*11.5 mm is designed and fabricated. The bandwidth of the filter is 120 MHz with the center frequency of 2.4 GHz and the insertion loss is less than -3 dB. Especially, the insertion loss is less than -20 dB from 2.8 GHz to 7 GHz. For the filters above, the simulated results and the measured results agree well.
A loss of large aperture quasi-optics which consist of a lens and a feed antenna is firstly measured using a radiometer receiver via the modified reference control method for a W-band imaging radiometer system. The quasi-optical loss is mainly decided by the dielectric loss of the lens with good quasi-optical transformation efficiency between the lens and the feed antenna. The quasi-optics composed of an aspheric lens and a dielectric rod antenna are designed for high resolution, low aberration, and compact size. The fabricated quasi-optics with the aperture diameter of 500 mm have the quasi-optical transformation efficiency of more than 95%. The radiometer receiver is designed applying a total power type and a direct conversion topology for simplicity, compact size and low temperature sensitivity. The manufactured receiver has the temperature sensitivity less than 1 K for both a hot source and a cold source. The calculated and measured results of the quasi-optics are very well matched by approximately 1.6 dB. The expected measurement errors by the reference control method are also analyzed as the functions of the characteristic parameters of the radiometer receiver.
Time harmonic electric and magnetic fields inside a parallel plate DB boundary waveguide are derived and fractional curl operator is utilized to study the fractional parallel plate DB waveguides. The DB boundary conditions are incorporated by assuming the behavior of boundary as perfect electric conductor (PEC) for transverse electric mode and perfect magnetic conductor (PMC) for transverse magnetic mode. For this purpose a general wave propagating inside the parallel plate wave waveguide is assumed and decomposed into TE and TM modes. Behavior of the fields and transverse impedances of the walls of guide are studied with respect to the fractional parameter describing the order of the fractional curl operator. The results are compared with the corresponding results for fractional waveguides with PEC walls.
This paper deals with the problem of detecting potential suicide bombers wearing concealed metallic and dielectric objects. The data produced by Millimeter-Wave-Radar system, working on a Multiple Frequency-Multiple Transmitters and Multiple Receivers configuration (MF-MTMR), is synthetically generated by an electromagnetic code based on Finite Differences Frequency Domain (FDFD) method. The numerical code provides the scattered field produced by the subject under test, which is later processed by using a multiple bistatic Synthetic Aperture Radar (SAR) algorithm. The blurring effect produced by the Point Spread Function (PSF) in the SAR image is removed by applying a regularized deconvolution algorithm that uses only magnitude information (no phase). Finally, the SAR algorithm and the deconvolution procedure are tested on a person wearing metallic and dielectric objects. The SAR response of dielectric rods is quite different from the metallic pipes. Our algorithm not only distinguishes between cases but also is capable of estimating the dielectric constant of the rods. Each constitutive parameter directly maps to the dielectric constant of explosive compounds, such as TNT or RDX, making feasible the detection of potential suicide bombers.
RF radiation due to corona and dry-band arc discharges have been observed using an antenna. Variations in radiated energy were observed due to change in the distance between two water droplets, the contact angle and the volume of the droplets, and the condition of the insulator surface. Changes in the frequency spectrum within the 800 MHz-900 MHz and 1.25 GHz-1.4 GHz frequency bands have been used to identify the transition from corona discharge to dry-band arc discharge. The 800 MHz-900 MHz emission band has also been used to monitor the condition of the insulator. These findings highlight the potential for RF sensing in the identification of partial discharges and insulator condition monitoring.
In this work, the enhancement in photonic band gap (PBG) in a dielectric-semiconductor photonic crystal (DS PC) is investigated. We consider two possible schemes that can be used to enhance the PBG in the near-infrared region. The first scheme is to add an ultrathin metal layer into the DS PC such that a structure of ternary metal-dielectric-semiconductor (MDS) PC is formed. The second scheme is to make use of the heterostructured PC. In scheme 1, it is found that the addition of metal layer will significantly move the left band edge to the shorter wavelength position, leading to an enlargement in the PBG. This enlargement can be extended as the thickness of metal film is increased. In addition, a pronounced enhancement in PBG is achieved when the metal with a higher plasma frequency is used. In scheme 2, we find that the PBG can be significantly enlarged compared to scheme 1. In addition, the increase in the band extension is shown to be four times larger than that in scheme 1. The results illustrate that, in order to enhance the PBG, the use of scheme 2 is superior to scheme 1. The enhancement of near-infrared (NIR) PBG is of technical use in the optical communications.
In this paper, a new method to analyze arbitrary shaped microstrip patch antennas is introduced. This method uses the multiport network model (MNM) together with a mathematical approximation called the "Pade approximation" such that the antenna input impedance obtained from the multiport analysis is approximated as a rational function of polynomials. Then, the roots of the denominator of this rational function are used to determine the antenna resonant characteristics. This new method is more time efficient than the standard multiport analysis because the evaluations are made at a single frequency. In the standard method, evaluations are made at multiple frequency values throughout the analysis. Results obtained by the new method are verified using the examples of rectangular and slot loaded compact microstrip patch antennas. Computational efforts for both procedures are presented.
This paper investigates the radial force characteristics of a novel two-phase dual layer switched reluctance generator. The proposed generator consists of two magnetically dependent stator and rotor layers, where each stator set includes four salient poles with windings wrapped around them while, the rotor comprises of two salient poles. In this paper, the radial and tangential force components and their trends in healthy condition under different load levels are assessed with the respect to critical rotor positions. One of the most important problems seen in the industrial applications of generators which have concerned users is the rotor eccentricity which may conclude the unbalanced distribution of flux linkage as well as acoustic noise and vibration due to the radial forces produced during the rotation of machine's rotor. In this regard, in this paper, it is attempted to obtain and evaluate the radial force components resulted from different degrees of eccentricity faults.
In this paper, we propose Modified Interpolated Spatial Smoothing (MISS) algorithm that solves the problem when the inhibition gain generated by Interpolated Spatial Smoothing (ISS) algorithm is not sufficiently high in virtual antenna adaptive beam forming to suppress coherent interference. Using the subspace projection concept, this paper establishes an interference subspace spanned by the interference steering vectors of the virtual antenna array, and then the interference direction information can be imported into the transformation matrix by projecting the transformation matrix into the subspace, which will make the interference components in virtual smoothing covariance matrix enhanced as it is demonstrated by theoretical analysis. Employing the Minimum Variance Distortionless Response (MVDR) beam forming method, the interference inhibition gain and Signal to Interference and Noise Ratio (SINR) performance can be significantly improved.
This paper describes the performance characteristics and comparison results of three different types of two-phase switched reluctance motors (SRM). This collection includes conventional, stepped rotor and slanted rotor two-phase SRMs. These motors have four stator poles and two rotor poles, named 4/2 configuration. The main difference between these configurations is their rotor structures. The number of turns and areas of all stator pole faces jointly involving in torque production mechanism in the motors are taken to be equal. The terminal inductance per phase, flux linkage of each stator pole winding, and components of leakage inductances are determined and plotted for different rotor positions and excitation currents. Finally, the static torque for different forced current levels and rotor positions are also presented for each motor.
In this paper, a compact notched ultra-wideband (UWB) bandpass filter with improved out-of-band performance using quasi electromagnetic bandgap (EBG) structure is proposed. Firstly, a UWB bandpass filter based on a stepped-impedance stub-loaded resonator (SISLR) is combined with quasi-EBG structures, which suppress the undesired spurious bands to improve the out-of-band performance. In order to eliminate the interference caused by WLAN, a notched band is introduced at 5.2 GHz, which is implemented by adding a folded stepped-impedance resonator (SIR) near the stub of the SISLR. At last, the proposed filter is fabricated and measured. Good performances of the UWB filter have been demonstrated both in the simulated and measured results.
In this paper, an analytic frequency domain method based on Taylor's series expansion approach is introduced to analyze inhomogeneous planar layered chiral media for an arbitrary linear combination of TM and TE polarizations. In the presented method, electromagnetic parameters of inhomogeneous chiral media and also the electric and magnetic fields are expressed using Taylor's series expansion. Finally, the validity of the method is verified considering some special types of homogeneous and inhomogeneous chiral media and comparison of the obtained results from the presented method with the exact solutions.
A wave-based inversion algorithm for the recovery of deviation in he values of elements of discrete lossless inductance-capacitance and capacitance-inductance ladder networks from their nominal values is formulated. The algorithm uses ultra wideband source excitation over the frequency range where forward and backward voltage and current waves propagate along the network. Employing a weak type scattering formulation renders the voltage wave reflection coefficient to be a Z transform of the sequence of perturbation in the value of the elements. Inversion of the reflected date from the transformed domain to the spatial domain by Fourier type integration yields the element's perturbations and consequently, the actual elements of the network. Demonstrations of the algorithm performance on several test cases show its efficacy as a non-destructive testing tool.
In this paper, a new method is proposed to estimate the simultaneous switching noise (SSN) directly from the power delivery network (PDN) frequency-domain impedance in order to reduce the time-domain simulation of SSN and computational burden, which is based on the periodic characteristics of the switching current and the SSN produced by one current pulse. The frequency-domain impedance is approximated with several single resonance circuits, which can capture the resonance characteristics of the PDN. The parameters of each resonance circuit are calculated with the rational function. It is also found that the SSN can be suppressed through adjusting the resonant frequencies and the period of switching current. Compared with the single resonance lumped circuit model and multi-resonance distributed circuit model, the performance of the new method for estimating the SSN is verified, which is more accurate than the target impedance method.
Split-field finite-difference time-domain (SF-FDTD) meth-od can overcome the limitation of ordinary FDTD in analyzing periodic structures under oblique incidence. On the other hand, huge run times of 3D SF-FDTD, is practically a major burden in its usage for analysis and design of nanostructures, particularly when having dispersive media. Here, details of parallel implementation of 3D SF-FDTD method for dispersive media, combined with total-field/scattered-field (TF/SF) method for injecting oblique plane wave, are discussed. Graphics processing unit (GPU) has been used for this purpose, and very large speed up factors have been achieved. Also a previously reported formulation of SF-FDTD based on the Drude model for dispersive media, is extended to cover Drude-Lorentz model, which is usually needed for materials such as gold. The resulting reduction in the number of variables in this formulation, not only helps in reducing the computational time, but also makes it possible to be implemented in GPU, where its memory limitation is a major concern. As an example for demonstrating the importance of this method in optimization of nanophotonics structures, improvement in the performance of a refractive index sensor, made of an array of nanodisks, using suitable angle of incidence is reported. To the best of our knowledge this is the first report of GPU implementation of SF-FDTD method, capable of analyzing periodic dispersive media under oblique incidence.
Closed-form mixed potential Green's functions (MPGFs) for cylindrically stratified media are derived in terms of quasistatic-wave and surface-wave contributions. In order to avoid possible overflow/underflow problems in the numerical calculations of special cylindrical functions such as Bessel and Hankel functions, a novel form of the spectral-domain MPGFs is developed. Then, a two-level methodology is used for the approximation of the spectral-domain MPGFs. In the first step, the qusistatic components are extracted from the spectral-domain MPGFs, and then transformed into the space domain with the use of the Sommerfeld identity and its derivatives. In the second step, the remaining parts of the spectral-domain MPGFs are approximated in terms of pole-residue expressions via the rational function fitting method (RFFM). The proposed method is efficient and fully automatic, which avoids an analytical cumbersome extraction of the surface wave poles (SWPs), prior to the spectrum fitting. In addition, this method can evaluate the spatial-domain MPGFs accurately and efficiently for both the near- and far-fields. Finally, numerical results for the spatial-domain MPGFs of a two-layer structure are presented and discussed.
Metamaterials are artificially structured electromagnetic materials which can lead to the realization of phenomena that cannot be obtained with natural materials. In the terahertz frequency regime, metamaterials have distinguished performance and open up a new way to design and construct the functional devices. Based on the structure of metamaterials, planar symmetric normal and complementary three-resonance resonators in Terahertz band are proposed in this paper. Simulation and experimental study have been carried out. The results show that the proposed structure has three distinct and strong resonant bands in THz regime and that symmetric normal structure and complementary structure can realize the three stop-resonances and pass-resonances respectively. For the well-separating of different resonances in the terahertz band, these symmetric three-passband and three-stopband resonators will be used in the design of multiband terahertz devices.
This paper presents results of a study to characterise wireless point-to-point channel for wireless sensor networks applications in sport hard court arenas, grass fields and on roads. Antenna height and orientation effects on coverage are also studied and results show that for omni-directional patch antenna, node range is reduced by a factor of 2 when the antenna orientation is changed from vertical to horizontal. The maximum range for a wireless node on a hard court sport arena has been determined to be 70 m for 0 dBm transmission but this reduces to 60 m on a road surface and to 50 m on a grass field. For horizontal antenna orientation the range on the road is longer than on the sport court which shows that scattered signal components from the rougher road surface combine to extend the communication range. The channels investigated showed that packet error ratio (PER) is dominated by large-scale, rather than small-scale, channel fading with an abrupt transition from low PER to 100% PER. Results also show that large-scale received signal power can be modeled with a 2nd order log-distance polynomial equation on the sport court and road, but a 1st order model is sufficient for the grass field. Small-scale signal variations have been found to have a Rice distribution for signal to noise ratio levels greater than 10 dB but the Rice K-factor exhibits significant variations at short distances which can be attributed to the influence of strong ground reflections.