Testing electronic equipment for radiated emissions requires the accurate calibration of EMI sensor. The performance of the sensor depends on its Antenna Factor (AF), which is the ratio of the incident electric field on the antenna surface to the received voltage at the load end across 50Ω resistance. The theoretical prediction of the AF of EMI sensors is a very attractive alternative if one takes into consideration the enormous expenditure and time required for calibrating a sensor experimentally. In this work, FDTD is developed to predict the performance of rectangular waveguide for EMI sensors.
The electromagnetic scattering from a conducting object coated with metamaterials, which have both negative permittivity and permeability is derived rigorously by using finite difference frequency domain (FDFD). A formulation for the FDFD method is presented. The scattering from circular and multilayers elliptic cylinder coated by metamaterial are investigated. Also, the scattering from dielectric and metamaterial sphere is depicted. Numerical results are compared with the available data in the literature.
A proposed sensor for landmines detection consists of two parallel microstrip antennas placed on the same ground plane and with corrugated ground surface between the arrays has been investigated. The microstrip patch array with corrugated ground surface has the advantage of a low mutual coupling compared with the classic arrays. The Finite-Difference Time-Domain (FDTD) is used to simulate the sensor for landmines detection.
In this paper, three analytic closed form solutions are introduced for arbitrary Nonuniform Transmission Lines (NTLs). The differential equations of NTLs are written in three suitable matrix equation forms, first. Then the matrix equations are solved to obtain the chain parameter matrix of NTLs. The obtained solutions are applicable to arbitrary lossy and dispersive NTLs. The validation of the proposed solutions is verified using some comprehensive examples.
Setting up ground based antennas for operation in the HF and longer wavelength bands frequently involves clearing large areas of land for the installation of ground mats to provide a high conductivity return path for the displacement currents. In moving from the cleared area to the virgin scrubland beyond, which is assumed to be forested with bushes and small trees, there is the possibility of an abrupt change in surface properties at the boundary resulting from the discontinuity in the vegetation which at longer wavelengths can be modelled as a change in surface impedance. By modelling the trees and bushes as point dipole moments, the aim of this paper is to estimate the significance of any such effect in terms of the gross physical properties of the vegetation. The result is to show that in normal circumstances the effect can be expected to be slight. A solution to this problem has application in helping determine the environmental footprint of the antenna installation, the amount of land that needs to be cleared to satisfactorily accommodate it.
Spatial focusing characteristics of time reversal (TR) electromagnetic waves are studied in this paper. Different antenna arrays are used as a TR mirror and their elements are arranged in one and two dimensions in the horizontal plane. The focused energy density around initial source location is investigated in non-line-ofsight (NLOS) and line-of-sight (LOS) cases, respectively. The results demonstrated that, roughly speaking, under the case of fixed space between two adjacent elements, the more the number of the array elements, the stronger the focused average energy density. However, in the case of fixed TR mirror array aperture, some abnormal phenomena are observed when additional elements are inset into the initial one.
A phase-alignment system is used fully integrate a power amplifier, Cartesian feedback linearization circuitry, and a phasealignment system. The phase-alignment system employs a new technique for offset-free analog multiplication that enables it to function without manual trimming. This paper demonstrates how the phase-alignment system improves the stability margins of the fully integrated Cartesian feedback system. The power amplifier itself, integrated on the same die, operates at 1 GHz and delivers a maximum of 30 dBm of output power into a 50-load. The class AB design for open loop and close loop power amplifier with Cartesian feedback, demonstrated a good linearity of 50 dBc and 80 dBc, respectively. The operating power is 2 W at 1000 MHz frequency.
In this paper, a Medium Access Control (MAC) protocol is proposed to investigate Quality of Service (QoS) for multimedia traffic transmitted over Ultra Wide-Band (UWB) networks and increase the system capacity. This enhancement comes from using Wise Algorithm for Link Admission Control (WALAC) which has three suggested versions. The QoS of multimedia transmission is determined in terms of average delay, admission ratio, loss probability, utilization, and the network capacity. In addition, a new parameter is aroused for the network performance. Comparisons between the IEEE 802.15.3a protocol and the proposed one are done. The proposed protocol shows better results in both sparse and dense networks for real time traffic transmission.
A microstrip 180^{o} phase shifter obtained by a novel design of Microstrip-to-Coplanar Waveguide (CPW)-to-Microstrip transition is presented. The proposed phase shifter is obtained without changing the layer of the second microstrip line. Via holes are used to transfer the current from the top to the bottom substrate layer and vice versa. The presented phase shifter is operating in a wide bandwidth between 5.5 and 18 GHz, with low insertion loss and reflection coefficients. Because the input and output microstrip lines are on the same layer, the presented phase shifter is suitable for a modified class of feeding networks for phased antenna arrays.
In this paper, two new line-fed loaded planar antennas are proposed for ultra-wideband applications. The first antenna is a circular patch with a circular ring as a Defected Ground Structure (DGS). A 50 Ohm microstrip line passes through the antenna which is symmetrical between the feed and the load. The impedance bandwidth of the first antenna with S11 < -10 dB is more than 10 GHz, from 3 GHz to more than 13 GHz, in both simulation and measurement. It will be shown that the antenna has quite a stable radiation pattern and also high gain over its bandwidth. The second configuration is a rhomboidal patch which a 50 Ohm microstrip line passes through it. A rhomboidal DGS ring is employed to widen the bandwidth of the proposed antenna. The impedance bandwidth with VSWR < 2 is more than 10 GHz, from 3 GHz to more than 13 GHz, in both simulations and measurement. The second antenna has also quite a stable radiation pattern and high gain values in its frequency band. For these antennas, a wideband 50 Ohm load has been used. Finally, it should be mentioned that the antennas have very compact structures as well as very simple configurations.
The Goos-Hanchen shift on the surface when an optical beam is obliquely incident from one isotropic right-handed material (RHM) into another biaxial anisotropic left-handed material (BALHM) is numerically studied with the finite difference time domain (FDTD) method based on the Drude dispersive models. The analytical expression of the Goos-Hanchen shift is firstly presented, moreo ver the condition for the existence and the sign of the Goos-Hanchen shift are also discussed. According to the theoretical analysis,sev eral sets of constitutive parameters of BA-LHM are considered. The simulated results are in agreement with theoretical results, which validate the theoretical analysis.
A Neural Network architecture is applied to the problem of Direction of Arrival (DOA) and state of polarization estimation using a uniform circular cross and tri-crossed-dipoles antenna array. A three layer Radial Basis Function Network (RBFN) is trained with input output pairs. The network is then capable of estimating DOA not included in the training set through generalization and the corresponding state of polarization. This approach reduces the extensive computations required by conventional super resolution algorithms such as MUSIC and is easier to implement in real-time applications. The results suggest that the performance of the RBFNN method approaches the exact values. In real time, fast convergence rates of neural networks will allow the array to track mobile sources.
The paper reports on investigations into new schemes for dimensional scaling of the elements of a microstrip reflectarray to obtain a slower slope of the reflected wave phase characteristic. First, the phase response as a function of various shape elements is investigated when only one of their dimensions is varied. Next investigations concern the case when two dimensions or features of the element are scaled in a certain manner simultaneously. In the latter case, it is shown that phase responses of lower slopes with a minimal range reduction can be obtained. The feasibility of this concept is illustrated for dipoles, rectangular patches, and square and circular rings. Comparisons of the obtained results show that twodimensionally scaled square and circular rings offer much better phase responses than those observed for dipoles and patches.
In this paper the simulation of ultra wideband microstrip antenna is considered. Because of the ultra wideband characteristics of this antenna, it is better to use time domain simulation methods. In this work we use three dimensional transmission line matrix method (3D-TLM) and EPML-TLM algorithm for modeling PML boundary condition directly applied to TLM algorithm. Finally simulation results of some kinds of this antenna (e.g., linear tapered slot antenna and modified planar inverted cone antenna) are presented and compared with measurements and some commercial software's output.
The shielding effectiveness (SE) measurements on enclosures with various apertures by both reverberation chamber (RC) and GTEM cell (GC) methodologies are presented. Furthermore, computer simulation through commercial software (CST) is used to compare with the experimental data. Our results show that the SE of the rectangular enclosure with five different apertures from RC is usually larger than those from GC. The reason for this is related to the random polarization and various angles of incidence within the RC, where various polarization and incident angles are averagely and randomly coupled into the EUT. However, as for the GC, the normal incidence with vertical polarization usually corresponds to the worse case, which leads to the worse SE of the enclosure. Surprisingly, an abnormal phenomenon is found from the enclosure with nine periodic rectangles. According to Charles F Bunting's work, moreover, it is still reasonable because many rectangular apertures on the enclosure may lead to a fact that the coupled energy of oblique incidence may be larger than that of normal incidence. Finally, we obtain conclusions about the use of two experimental methodologies in SE measurement.
An effective computational method based on a conventional modal expansion approach is presented for handling a multilayered dielectric grating whose profiles are multilayered and sinusoidally modulated. This structure fabricated by dielectric material is one of the useful photonic crystals. The method is based on Yasuura's modal expansion, which is known as a least-squares boundary residual method or a modified Rayleigh method. In the extended method, each layer is divided into shallow horizontal layers. The Floquet modal functions and approximate solutions are defined in each shallow layer, and the latter are matched with boundary conditions in the least-squares sense. A huge-sized least-squares problem that appears in finding the modal coefficients is solved by the QR decomposition accompanied by sequential accumulation. This procedure makes it possible to treat the case where the groove depths are the same as or a little more than the grating period. As numerical example, we calculate a diffractive characteristic by a multilayered deep dielectric grating and confirm that a common band gap occurs for both polarizations.
In this paper we introduce general numerical analysis for investigation the performance of avalanche photodiodes (APD) while we change the multiplication region mole fraction. We have found that the gain, breakdown voltage, and performance factor, at a given bias voltage, increase while the excess noise factor decreases through the decreases in fraction of Al in Al_{x}Ga_{1−x}As-APDs. For calculation the characteristics of Al_{x}Ga_{1−x}As-APDs we use the dead space multiplication theory (DSMT) and width independent ionization coefficient.
Anew multimodal variational formulation (NVMF) analysis is used for a rigorous analysis of four microwave subsystems with multiple discontinuities: one double-step and one quadruplestep empty-ridged waveguide discontinuity, one iris-coupled cavities filter with four resonators and one impedance transformer. The sparameters of each structure are deduced from its total impedance matrix, without cascading the S-parameters of individual discontinuities as with the most methods based on mode-matching technique; the convergence study versus the accessible modes is no long necessary, which makes this passive microwave circuit's analysis and design tool very efficient.
This paper outlines basic principle of Synthetic Aperture Radar (SAR). Matched filter approaches for processing the received data and pulse compression technique are presented. Besides the SAR radar equation, the linear frequency modulation (LFM) waveform and matched filter response are also discussed. Finally the system design consideration of various parameters and aspects are also highlighted.
This paper, which had been published on Progress In Electromagnetics Research B, Vol. 2, 15{26, 2008, was withdrawn on April 12, 2011 due to confirmed self-plagiarism.
Modifications in the measurement of the complex permittivity are described, based on the transmission and reflection coefficients of a dielectric slab. The measurement uses TRL twoport calibration to bring the reference planes accurately to the sample surface. The complex permittivity as a function of frequency is computed by minimizing the difference between the measured and the ideal scattering parameters. An alternative procedure for determining the complex permittivity uses the fractional linear data fitting to a Qcircle of the virtual short-circuit and/or virtual open circuit data. In that case, the sample must be a multiple of one-quarter wavelength long within the measured range of frequencies. Comparison with results obtained by other traditional procedures is provided.