In this contribution, a two step strategy for the inversion of amplitude-only data in microwave imaging applications is analyzed. At the first step of the proposed method, the illuminating source is synthesized according to a line sources model in order to compute the incident field in the investigation domain starting from the values available in the measurement domain. The second step is aimed at reconstructing the profile of the objects under test thanks to the iterative multi-scaling approach integrated with the Particle Swarm Optimizer, an effective evolutionary minimization technique. The reconstruction accuracy of the proposed phaseless retrieval strategy is analyzed using synthetic data concerned with a multiple scatterer configuration and successively further assessed inverting experimental data.

This paper presents comprehensive measurements of radar backscatter from rice crops using a ground-based 6 GHz C-band scatterometer system. The measurements were conducted over an entire season from the early vegetative stage of the plants to the ripening stage with full polarization combinations of HH, VV, HV and VH at the incident angle range from 0^o to 60^o. The objective of this paper is to access the use of the ground-based scatterometer data for the investigation of temporal variation of different incident angle in the rice growth monitoring application. A further study on the angular response for different rice growth stages was also performed in order to have a better understanding of the backscattering behavior of the rice crops and therefore, monitoring of rice crops growth using operational scatterometer system.

In this paper we study the behavior of wave radiation of a horizontal electric dipole antenna with grounded metamaterial substrates formed by using coordinate transformation technology. From theoretical analysis and simulation results, we can find that such metamaterial substrates not only improve the directive emission but also enhance the radiation efficiency as the dipole antenna gets closer and closer to the metallic ground plane. We thus demonstrate that the transformation medium can offer a theoretical basis for designing a compact planar antenna with transformation media as substrates.

New electromagnetic models for the rods and cones that are the photoreceptors at the back of the retina are developed and simulated in order to explain the roles of dimension, geometrical structure, directional sensitivity and visual pigments of the photoreceptors in the reception of visible light. The rods and cones are modeled as uniform and quasi-tapered helical antennas, respectively. The results of the model study show that if the model antennas have the original photoreceptor cell dimensions, the frequency responses of the model antennas and the spectral sensitivities of the photoreceptors would be very close to each other. In addition, it's observed that the spectral sensitivities of L, M and S cones are broadband over the visible light spectrum, and there are secondary peaks beside main peaks in the spectral sensitivity curves of the cones, because of the conical shape of the cones. It's also observed that there is only one main peak in the spectral sensitivity curves of the rods, because of the uniform and cylindrical shape of the rods. Finally, an array of the novel modeled antennas is also discussed to be used in biomedical applications of artificial retinal photoreceptors in medicine, although the main scope is not designing artificial retinal photoreceptor prosthesis.

The Development of numerical techniques enables us to analyze a large number of complex structures such as dielectric resonator (DR) filters and planar passive elements for coplanar monolithic microwave integrated circuits. As for DR filters, numerical analysis of these structure is highly intricate mostly because of their non-homogenous composition (dielectric constant of DR is greater than 80, dielectric constant of the maintainer is less than 2 and dielectric constant of the atmosphere is 1). Hence, numerical analysis of such a structure, either in time domain (TLM, FDTD and . . . ) or frequency domain (FE, moment, mode matching, boundary element, FD and . . . ) is both complex and time-consuming. From one hand, the non-homogenous structure and from the other hand, the high frequency of applications, demand high density meshing in order to achieve accurate response [1-3]. The explained method in this paper enables us to design a Chebyshev band passes filter by coaxially placing high-Q TM_01δ dielectric resonators in a cutoff circular waveguide. In the presented work, discussions are made regarding high-Q resonators and interresonator coupling. It can be used for TE and TM modes of dielectric resonators. The advantages of such a method are simplicity and accuracy. Furthermore, this method is very quick in calculating resonant frequencies of a single dielectric resonator and coupling factor between two dielectric resonators. Compared with HFSS software, the total required time in this method is less than 1 percent. Based on the presented method, a DR filter is designed, implemented and fabricated and the results are provided. The fabricated filter has an exclusive feature, i.e., it contains no screw for frequency tuning and it gives out the desired result without a need to modification.

In this paper, we apply the Shannon wavelet basis functions to the method of moments to evaluate the radar cross section (RCS) of the conducting and resistive surfaces. The problem is modeled by the integral equations of the first or second kind. An effective numerical method for solving these problems based on the moments method and using Shannon wavelet basis functions is proposed. The validity and accuracy of the method is checked on some examples, and the Shannon wavelets are compared with the well-known block-pulse functions (BPFs) from the viewpoint of computational efficiency. The problem of evaluating the RCS is treated in detail, and illustrative computations are given for some cases. This method can be generalized to apply to objects of arbitrary geometry and arbitrary material.

In the present work, a precise optimization method is proposed for tuning the parameters of ITU-R P.1546 recommendation to improve its accuracy in VHF and UHF propagation prediction. In this optimization method, the genetic algorithm is used to tune the model parameters. The predictions of the tuned model are compared with those of the ITU-R P.1546 recommendation and verified in comparison with some electric field strength measurements obtained by utilizing the IS-95 pilot signal in a commercial CDMA network in rural Australia.

In this paper, the region of interest consists of a perfect conductor, coated with the two layer dielectrics under the air. The completed analytical formulas have been derived for the electromagnetic field due to a vertical electric dipole in the four-layered region when both the source point and observation point are located in the upper dielectric layer. Similar to the three-layered case, the trapped surface wave, which is contributed by the sums of residues of the poles, can also be excited efficiently by a vertical electric dipole in the four-layered region. The lateral wave is determined by the integrations along the branch cuts.

Copper-cobalt ferrites with general chemical formula Cu_xCo_1-xFe₂O₄ (with x = 0.0, 0.4, 0.6 & 1.0) were prepared by ceramic method. The solid state reaction was confirmed by XRD patterns. DC conductivity was measured by two probe method. Electrical resistivity is found to increase on lowering of sintering temperature and time. At x = 1.0, the conduction is mainly due to hopping of electrons leading to n-type conductivity while at x = 0.0, conduction is due to holes leading to P-type conductivity. The lowest conduction at x = 0.4 is attributed to the electron hole compensation. SEM micrographs were obtained from JEOL scanning electron microscope. The micrographs reveal that an average grain size increases with sintering temperature and time as a result of decrease in porosity. This leads to the decrease in resistivity with sintering temperature and time. One of the factors for higher conductivity in ferrites is an increase in average grain size and decrease in pore concentration during the heat treatment.

An effective method for improving the characteristics of the microstrip parallel coupled line coupler is proposed. Some grooves are oriented parallel to the strips and just next to them. It can be shown that an appropriate depth of the grooves can be used for equalizing the even- and odd-mode phase velocity in a coupled microstrip lines with proper geometrical dimensions. Sets of design graphs are derived for various depths of grooves as a parameter and with curves that implies phase velocity equalization curves. The simulated scattering parameters for couplers in conventional and proposed topology show the efficacy of the new grooved substrates.

By properly exciting higher order modes at an aperture it is possible to achieve higher aperture efficiencies. High efficiency antennas are mandatory in many applications, as discrete lenses, since the single element efficiency deeply affects the efficiency of the whole lens. In this contribution a genetic algorithm is applied to the mode matching analysis of square horns to achieve high radiation efficiency over a relatively wide band.

Anew wideband and compact bandstop filter using one dimensional (1-D) mushroom-like electromagnetic bandgap (EBG) structures is proposed in this paper. Although the proposed structure can not be fabricated as easy as defected ground structure (DGS) filters, it has several winning features such as more compactness, better characteristics and no backward radiation. A5-cell 1-D mushroomlike EBG filter is compared with 5-cell and 9-cell circular DGS filters. The 1-D mushroom-like EBG filter is found to be more compact as it requires fewer cells for the same characteristics and also as it has 0.44 times shorter cell length. The proposed EBG filter has a 10-dB bandwidth of 39% while the 5-cell and 9-cell DGS filters have 10-dB bandwidth of 20% and 27%, respectively. Also, the 1-D mushroom-like EBG filter is studied for various number of cells and compared with a two dimensional (2-D) structure. The simulated and measured results are found to be in good agreement.

A novel technique to increase the bandwidth of the conventional planar triangular monopole antenna (PTMA) is presented. With two symmetrical corrugations extended from the flat ground plane, a significant improvement on the impedance bandwidth up to about 4:1 can be achieved. The proposed antenna design is a modification from the conventional volcano smoke antenna (VSA) and can be more compact and easily fabricated. The HFSS 3-D EM solver is employed for design simulation. The effects of the ridged ground plane on the impedance bandwidth are studied. A printed PTMA is fabricated on the FR-4 PCB substrate. Measured VSWR of the printed PTMA with the ridged ground plane is less than 2 from 3 to 12 GHz which covers the UWB frequency band. The measured antenna patterns also show the monopole-type omni-directional radiation patterns from 3 to about 10 GHz.

A new technique is proposed to increase the bandwidth (BW) of slot antenna operated at 2.4 GHz and 5 GHz, over the industrial-scientific-medical (ISM) bands and the Hiperlan2 bands. By splitting two side slots of the Z-like slot antenna into two or three fingers, several additional resonances can be created. By properly arranging the geometry of the feeding structure in the multi-slot region, the double-slot and triple-slot antennas have respectively 2.0 and 3.2 times wider bandwidth than the single Z-slot antenna. According to the results, the proposedtriple-slot antenna can provide two separated impedance bandwidths of 672 Hz (about 28.3% centered at 2.4 GHz band) and 2752 MHz (about 53.5% centered at 5.2 GHz band), making it easily cover the required bandwidths for WLAN operation in the 2.4 GHz bandand 5.2/5.8 GHz bands.

In this paper, a novel stochastic approach, i.e., the electromagnetism-like (EM-like) algorithm, is applied to phase-only syntheses of antenna arrays. The goal is to minimize the pattern sidelobe under null-steering constraints by phase-only adjusting. The mechanism of EM-like algorithm results from the Coulomb's Law of Electromagnetics. It does not require gradient calculations, and can automatically converge at a good solution through the virtual charge of each particle. Simulation results show that the EM-like algorithm can well treat the phase-only optimization of antenna arrays. Although the null-steering constraints will affect the optimization in sidelobe reduction, it can be easily included in the EM-like based optimization scheme. The EM-like algorithm can be applied not only to problems of antenna arrays, but also to many other nonlinear optimization problems in electromagnetic waves.

A very small patch type RFID tag antenna (UHF band) using ceramic material and proximity coupled feeding structure mountable on metallic objects is presented. The proposed tag size is 25×25×3 mm. Both of the radiating part and the feeding part of the proposed antenna is located in the same plate for easy implementation. The resistive and reactive components of the input impedance of the antenna can be easily matched to the tag chip impedance from the size of the feed loop and the distance between feed loop and radiating patch. The antenna satisfactorily operates on metal plates, so it is applicable in many applications. The proposed design is verified by simulation and measurements which show good agreement.

A compact ultra-wideband (UWB) band-pass filter (BPF) with highly rejected notched band is proposed in this paper. The proposed UWB BPF is composed of two cascaded interdigital hairpin resonator units. Interdigital hairpin resonator unit with different coupling is theoretically analyzed. The working frequency of the proposed UWB BPF is 3.1-10.6 GHz and notched band is 5.7-5.8 GHz. Finally, measured results are presented, which are in good agreement with the simulation results.

Geometrical analyses of basic equations of electromagnetics waves propagation in anisotropic dielectric materials with magnetic isotropy are presented in two complementary papers (Part I and Part II). In the present one, analysis arises from quadrics associated with relative dielectric tensor (ε) compatible with conical surfaces that represent the general plane wave equation (relation of dispersion). This study systematizes rays propagation in left-handed materials (LHMs) exhibiting dielectric anisotropy and magnetic isotropy. In particular, indefinite dielectric media where dielectric permittivities are not all the same sign, have been investigated. Graphical alternative procedures for ray tracing in these media are presented.

Asymptotic techniques have been successfully applied to compute electromagnetic wave radiation in various high-frequency engineering domains. Recent approaches based on Gaussian beams for tracking fields may overcome some problems inherent to the ray methods such as caustics. The efficiency of these methods is based on the ability to expand surface fields into a superposition of Gaussian beams. However, some difficulties may arise when the surface is curved. In this paper, we propose a new efficient way to expand fields on a curved surface into Gaussian beams. For this purpose, a new beam formulation called Conformal Gaussian Beam (CGB) is used. The CGBs have been developed to overcome the limitation of the expansion into paraxial Gaussian Beams. The analytical Plane-Wave Spectrum and far-field of a CGB are derived and compared with numerical calculations. A brief parameter analysis of the CGBs is realised.

Geometrical analysis of basic equations of electromagnetics waves propagation in anisotropic dielectric materials with magnetic isotropy are presented in two complementary papers (Part I and Part II). In this paper, analysis arises from local properties of dielectric permittivity tensor and Mohr's plane graphical construction compatible with circumferences that represent general plane wave equation. This theoretical study allows to know how rays propagate in left-handed metamaterials (LHMs) exhibiting dielectric anisotropy and magnetic isotropy. Geometrical analysis yields plane graphical procedures for ray tracing, that are extremely easy. In particular, indefinite dielectric media, where dielectric permittivities are not all the same sign, has been investigated and a joint study of materials having the same eigenvalues of ε, but with opposite values of μ_r is performed. The opposite sense of propagation of rays in "opposite media" (media with opposite values of ε_i and μ_r) has been also shown. It must be pointed out that the presented method always allows graphical plane constructions, even when dealing with biaxial media.