This paper presents an improved approach for the propagation of electromagnetic (EM) fields along a helical dielectric waveguide with a circular cross section. The main ob jective is to develop a mode model for infrared (IR) wave propagation along a helical waveguide, in order to provide a numerical tool for the calculation of the output fields, output power density and output power transmission for an arbitrary step's angle of the helix. Another objective is to apply the inhomogeneous cross section for a hollow waveguide. The derivation is based on Maxwell's equations. The longitudinal components of the fields are developed into the Fourier- Bessel series. The transverse components of the fields are expressed as functions of the longitudinal components in the Laplace plane and are obtained by using the inverse Laplace transform by the residue method. The separation of variables is obtained by using the orthogonal- relations. This model enables us to understand more precisely the influence of the step's angle and the radius of the cylinder of the helix on the output results. The output power transmission and output power density are improved by increasing the step's angle or the radius of the cylinder of the helix, especially in the cases of space curved waveguides. This mode model can be a useful tool to improve the output results in all the cases of the hollow helical waveguides (e.g., in medical and industrial regimes).

Electromagnetic inverse scattering problems are compu- tation intensive, ill-posed and highly non-linear. When the scatterer lies in an inaccessible domain, the ill-posedness is even more severe as only aspect limited data is available. Typical algorithms employed for solving this inverse scattering problem involve a large scale non-linear optimization that generates values for all pixels in the investigation domain including those that might not contain any useful information about the ob ject. This communication is concerned with the local- ization in the investigation domain prior to inverse profiling of buried 2-D dielectric pipelines having circular cross section. A custom defined degree of symmetry is computed for each transmitter position, which is a measure of the symmetry of the measured (synthetic) scattered field vector. The degree of symmetry vector computed for a scat- terer is found to exhibit unique features for the geometric and electric properties of the dielectric pipeline. A probabilistic neural network is trained with the degree of symmetry vectors computed for different ob ject configurations. It classifies the test degree of symmetry vec- tor of the unknown scatterer presented to it into one of the classes that indicate the localized region in the investigation domain in which the pipeline is located. The Distorted Born Iterative procedure is em- ployed for imaging the pipeline that has been localized. The reduction in the investigation domain reduces the degrees of freedom of the in- verse scattering problem and the results are found to be much superior to those when the entire investigation domain is employed.

This research concerns offline identification of acoustic characteristics of enclosures with second-order resonant dynamics and their modeling as linear dynamic systems. The applied models can be described by basis function expansions. The practical problem of acoustic echo in enclosures is used as the target problem to be addressed. It has been found out that the classical filters are ineffective filter structures for approximating an echo generating system, due to their many required parameters. In order to reduce the number of estimated parameters, alternative methods for modeling the room impulse response need to be investigated. Out of various available techniques impulse response identification is utilized. With the help of given experimental data, the enclosures' impulse response is modeled using special orthonormal basis functions called Kautz functions. As another improved approximation, hybrid multistage system identifiers have been used in which the simplicity of classical filter structures and fast convergence of orthonormal structures is utilized as an advantage.

This second part will be devoted to the development of a bistatic synthetic aperture processing method for radar imaging. Indeed, we establish various process that the received signal must undergo in order to estimate the target reflectivity in the bistatic case. High resolution image is obtained by two treatments on the table image of the bistatic received signal developed in the companion paper. The detail of the image reconstructing by a BISAR will be presented in this paper. The interest of this model is important, because it permits for a defined scenario generation of radar data which can be used in signal processing algorithms for target detection, identification and mapping. We present the simulation results for various scenes. These results are obtained by using two algorithms developed for BISAR imagery. Then we present the experimental results.

Bistatic Synthetic Aperture Radar (BISAR) is an active imaging system for which the transmitting and the receiving antennas are located on separate platforms. During its motion, the transmitting antenna emits towards the ground a burst of pulses at a frequency called Pulses Repetition Frequency. Every pulse affects an area of the ground after a propagation time proportional to the distance transmitter-scene. The bistatic receiving antenna receives a signal from the ground after a propagation time proportional to the distance scene-receiver. A communication link between the transmitter and the receiver is necessary to measure the phase of the received signal with respect to that of the transmitted signal. This paper presents, initially, the modeling of a moving polarimetric radar working in bistatic configuration. We propose to write the received signal as a function of time for the general case where the transmitter, the target and the receiver are moving. As BISAR and MONOSAR (Monostatic Synthetic Aperture Radar) geometry differ substantially, the BISAR temporal requirements are examined in detail. The radiolink is completely modeled. The companion paper is devoted to the development of two processing methods for bistatic radar imaging. Simulation and experimentation will be presented.

This paper investigated comparatively the characteristics of four types of artificial magnetic conductor (AMC) surface, including a mushroom-like (electromagnetic band gap) EBG, uniplanar compact EBG (UC-EBG), Peano curve, and Hilbert curve, as a ground plane for a low-profile antenna. The AMC surface structures are designed to have an in-phase reflection property for a plane wave of normal incidence in the vicinity of 2.45 GHz. The bandwidths of the in-phase reflection for the AMC surfaces and return losses, radiation patterns, and gains of the horizontal wire antennas on the AMC ground planes are all measured and compared with each other. The measured data show that all the AMC surfaces act as good ground planes for a low- profile antenna, yet the bandwidth and gain of the mushroom-like EBG structure are broader and larger, respectively, than those of the other structures.

The paper is concerned with the development and mathematical justification of the methodology for applying the time- domain methods in the study of spectral characteristics of open electrodynamic resonant structures.

A completely automatically near-field mapping system is developed within IRSEEM (Research Institute for Electronic Embedded Systems) in order to determine electromagnetic field radiated by electronic systems. This test bench uses a 3D positioning system of the probe to make accurate measurements. The main element of this measurement tool is the probe. This paper presents a characterization of the open-ended coaxial probe which is used to measure the normal component of the electric field.

The diffraction of E-polarized plane waves by an impedance loaded parallel plate waveguide formed by a two-part impedance plane and a parallel half plane with different face impedances is investigated rigorously by using the Fourier transform technique in conjunction with the Mode Matching Method. This mixed method of formulation gives rise to a scalar Modified Wiener- Hopf equation, the solution of which contains infinitely many constants satisfying an infinite system of linear algebraic equations. A numerical solution of this system is obtained for various values of the surface impedances and waveguide height.

A Gaussian beam is an asymptotic solution to Maxwell's equations that propagate along a curve; at each time instant its energy is concentrated around one point on the curve. Such a solution is of the form

E = Re{e^iPθ(x,t)E₀(x, t)},

where E₀ is a complex vector field, P >0 is a big constant, and θ is a complex second order polynomial in coordinates adapted to the curve. In recent work by A. P. Kachalov, electromagnetic Gaussian beams have been studied in a geometric setting. Under suitable conditions on the media, a Gaussian beam is determined by Riemann-Finsler geometry depending only on the media. For example, geodesics are admissible curves for Gaussian beams and a curvature equation determines the second order terms in θ. This work begins with a derivation of the geometric equations for Gaussian beams following the work of A. P. Kachalov. The novel feature of this work is that we characterize a class of inhomogeneous anisotropic media where the induced geometry is Riemannian. Namely, if ε, μ are simultaneously diagonalizable with eigenvalues ε_i, μ_j , the induced geometry is Riemannian if and only if ε_iμ_j = ε_jμ_i for some i ≠ j. What is more, if the latter condition is not met, the geometry is ill-behaved. It is neither smooth nor convex. We also calculate Riemannian metrics for different media. In isotropic media, g_ij = εμδ_ij and in more complicated media there are two Riemannian metrics due to different polarizations.

The reconstruction of the frequency-dispersive constitutive parameters of general bianisotropic media is achieved by an optimization approach. The constitutive parameters are optimized in order to match the measured reflection and transmission data for plane wave incidence onto bianisotropic slabs. Two optimization methods, in our case the differential evolution (DE) algorithm and the Nelder-Mead simplex method, are used for the reconstruction at low frequencies. The Nelder-Mead simplex method is then used to obtain the solutions at higher frequencies, where the initial guess is obtained by the linear extrapolation of the solutions at previous frequencies. The proposed reconstruction method is tested with both noiseless and noisy data, and is proven feasible and robust.

In this paper, the regular microstrip-fed dipole antenna with simplified balun is modified to improve the usable bandwidth by increasing the stability of the radiation patterns. The presented antenna consists of two parallel dipoles of different lengths to obtain two main resonances. The distance between the two dipoles is adjusted to reduce the return loss between the two main resonances. A wide usable bandwidth of more than 84% is obtained with high radiation pattern stability. The proposed antenna is simple and small in size. The results of a modified two-element array configuration from this antenna show that it is very good candidate for wideband phased array applications.

An effective approach is suggested for calculating the Green's function of an axially symmetric sheet magnetic current placed on a circular cylindrical metal surface. Upon improving convergence of the available Fourier transform, it has been possible to explicitly develop the Green's function logarithmic singularity at the source. Also, the Green's function behavior at the branch point in the spectral domain has been considered, ending up with the singularity extraction in the space domain. It is shown that this branch point singularity (pole) corresponds to the cylindrical quasi-TEM mode of the cylinder exterior. Finally, the rest of the Green's function is effectively numerically calculated.

A vectorial modal analysis of two-dimensional (2-D) dielectric grating is presented. The transmission and reflection from the 2-D dielectric-grating slab are computed by combining the generalized scattering matrix and the modal analysis. New insights on the boundary conditions between two grating structures are presented to be suitable for two-dimensional gratings. The results obtained using the present analysis are verified with published experimental and numerical results for both one- and two-dimensional dielectric-grating slabs. The present approach provides fast convergence and provides good agreement with other numerical techniques. This technique is used to study the effects of different parameters for designing a wide band FSS composed of multilayered 2-D grating slabs.

A new method to improve the gain of circular waveguide array antenna with metamaterial structure is presented. The electromagnetic characteristics of metamaterial and circular waveguide antenna with metamaterial structure are studied by using numerical simulation method, which are also compared with those of the conventional circular waveguide antenna. The simulation and experimental results show that this method is effective and metamaterial structure can realize congregating the radiation energy, so the gain of the antenna increases while the side lobe level decreases.

The design of a compact, single feed, dual frequency dual polarized and electronically reconfigurable microstrip antenna is presented in this paper. A square patch loaded with a hexagonal slot having extended slot arms constitutes the fundamental structure of the antenna. The tuning of the two resonant frequencies is realized by varying the effective electrical length of the slot arms by embedding varactor diodes across the slots. A high tuning range of 34.43% (1.037-1.394 GHz) and 9.27% (1.359-1.485 GHz) is achieved for the two operating frequencies respectively, when the bias voltage is varied from 0 to -30 V. The salient feature of this design is that it uses no matching networks even though the resonant frequencies are tuned in a wide range with good matching below -10 dB. The antenna has an added advantage of size reduction up to 80.11% and 65.69% for the two operating frequencies compared to conventional rectangular patches.

In this paper a programmable beam-switching algorithm for planar phased array antenna is presented. Using micro-controller the planar array can be steered over 49 directions over the complete hemisphere. Each element is connected to delay lines and switching module. The bits at micro-controller output after being amplified by driver circuit are fed to the switching modules which control the insertion of fixed phase tapering. Switching is performed on a unique set of delay lines to steer the beam in particular direction in the horizon. For high frequency application PIN diode is used as switch. In total 12 bits are used to select 49 beam positions with some bit patterns being redundant.

In this communication a comprehensive study of the dielectric properties of human breast milk at microwave frequencies is reported. The samples are collected at weekly intervals following child birth. Measurements are made at the S -band of microwave frequency employing the rectangular cavity perturbation technique. The dielectric constants of the breast milk samples are found to increase as weeks elapse, which is attributed to the reduced fat content and increased lactose concentration. The conductivity of the breast milk samples is similarly found to increase due to the increased dilution.

A general method is proposed to frequency domain analysis of inhomogeneous two-dimensional periodic gratings. Each component of electromagnetic fields is expressed by several spatial harmonic plane waves. Then, two differential equations are obtained for the reflection and transmission matrices, using wave-splitting approach. Solving these equations gives us the co- and cross-polarized reflection and transmission coefficients. The method is studied using some examples.

In the present paper a simple model has been given to simulate the signal propagation through two cross orthogonal microstrip lines in two different layers of the PCB board. First the structure has been analyzed using full wave software like HFSS, then a simple and suitable lumped equivalent circuit is proposed for the cross talk region and its parameters are obtained. Finally the sparameters of this equivalent circuit compared with the results of full wave simulations. The results show good agreement up to some GHz.