This study analyzes polarizability properties of spherically layered small inclusions that possess negative permittivity. Conditions for invisibility to external electric fields are derived. The complementary principle for two-dimensional scatterers is used to derive special properties of self-complementary inclusions. A singular behavior between the limits of invisibility and infinite response is underlined for a hollow circular shell. A similar,although not as drastic,phenomenon is shown to take place for the three-dimensional hollow sphere.

Metamaterials with small electrical size are more feasible to be described by the macroscopic parameters and treated as an effective homogenous media. By using geometric optimization, we experimentally realize a metamaterial composed of crankled S-ring resonator,whose electrical size is 2.5 times smaller than the conventional S-ring resonator. The overall effective capacitance of the unit structure is greatly increased when viewed from an equivalent circuit model point of view,so the resonant frequency is decreased, and the metamaterial works at a much longer wavelength regime. In addition,w e summarize two kinds of other methods that could be used to reduce the electrical size of the structures. Experimental and simulation results are presented,sho wing the effectiveness of these methods in the metamaterial homogenization.

An efficient metal-insulator-metal (MIM) capacitor simple scalable model for use in monolithic-microwave integrated circuit (MMIC) design is presented in this paper. This model is based on transmission-line theory. Analytical expressions based on physical parameters have been given in detail. Nine different physical dimension capacitors are fabricated to verify the validity of the proposed model. A good agreement between measured result and simulated data is obtained.

This paper studies the performance appraisal of radiation performance of ultra low sidelobe level Active Phased Array Antennas in presence of Multilayer Flat Sandwich Radome. Further, the effect of errors introduced due to amplitude/phase quantisation and planarity of the array surface, on the radiation performance has been studied. Based on these errors, manufacturing tolerances of the Flat Sandwich Radome have been suggested to control the deterioration of radiation performance within tolerable limits. This work is expected to be useful in development/manufacturing of radomes for Active Phased Array Radars and similar applications where ultra low sidelobe levels are required to be maintained.

This paper presents an optimum design technique ofan asymmetric V-dipole antenna and it's a three-element Yagi-Uda array using Genetic Algorithm (GA). The optimization parameter for the V-dipole is the directivity and that for the Yagi-Uda array are the input impedance and directivity. The theoretical analysis has been done using a Moment-Method technique in a very simple step-by-step way, and subsequently the GA is applied for obtaining the optimized parameters. Comparative results are provided for 3-elements straight dipole Yagi and V-dipole Yagi array. Further, analysis for directivity with respect to included angle is given for the GA based optimization problem that gives an important aspect in the design of V-Yagi.

In this paper, a new tapered beamforming function for side lobe reduction in the uniform concentric circular arrays (UCCA)is proposed. This technique is based on tapering the current amplitudes of the rings in the array, where all elements in an individual ring are weighted in amplitude by the same value and the weight values of different rings are determined by a function that has a normalizedgaussian probability density function variation. This novel tapering window is optimized in its parameters to have the lowest possible side lobe level that may reach 43 dB below the main lobe and these optimum weights are found to be function of the number of elements of the innermost ring and the number of rings in the array. The proposed tapering window can be modified to compensate the gain reduction due to tapering when compared with the uniform feeding case.

A general circuit model is proposed for 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 and two boundary conditions are obtained for the electric and magnetic vectors. Finally a circuit model is introduced for the obtained equations. The circuit model consists of loaded and excited nonuniform coupled transmission lines (CTL).

A generalized equivalent circuit model for waveguide transverse slots is proposed for the efficient analysis of waveguide transitions and waveguide slot antennas and slot-excited antennas. The transverse slots on the broad and end waveguide walls analyzed in this paper are decomposed into three structures: two apertures and an auxiliary waveguide section. The slot aperture in the host waveguide is modeled as an inductance-capacitance-transformer (LCT) combination, for which the equivalent inductance and capacitance are determined by first considering the case of zero-thickness slot, then the transformer turns ratio is calculated for the slot on a finite thickness wall. The effect of the wall thickness is accounted for by a waveguide section having cross-sectional dimensions equal to those of the slot, and length equal to the wall thickness. The loaded slot aperture is modeled along with the external load as a lumped load impedance. Expressions for the inductance, capacitance and transformer turns ratio are obtained in terms of the slot length and width. The obtained expressions facilitate the design of a variety of structures, including waveguide couplers, feeding networks and radiators. The equivalent circuit model proved to be accurate compared to the method of moments solution over a wide frequency band. Comparison of the scattering parameters obtained from the circuit analysis, the method of moments, and the finite-difference time-domain solutions exhibit very good agreement.

A kind of microstrip array double-antenna (MADA) and its corresponding radar front-end are presented in this paper. The double-antenna comprises two individual 4-patch arrays which are coplanar in a round substrate with 25mm diameter and are used as receiver antenna and transmitter antenna respectively in 36 GHz radar front-end. Both simulation and test results of the antenna are exhibited, which shows better isolation between two arrays below −42 dB in a wide band. Test results of radar front-end with MADA are also presented, from which we can see perfect performance the system has. With improvement of radar system, a more compact MADA with 18.6mm diameter is designed, fabricated and measured, which shows a good response.

This paper discusses the analysis of a novel two-segment rectangular dielectric resonator antenna (DRA) for broadening of the impedance bandwidth. In the proposed configuration, two rectangular dielectric sections are used which are separated by a metal plate. With this configuration, it is possible to excite two adjacent resonant frequencies. Utilizing the two-segment thin DRA and skillfully varying its aspect ratio, an appropriate structure is obtained that illustrates more than 76.8% impedance bandwidth (for S₁₁>10 dB) at 3.32- 7.46 GHz frequency band.

In this paper, a new structure is proposed for microwave filters. This structure utilizes a waveguide filled by several dielectric layers. The relative electric permittivity and the length of the layers are optimally obtained using least mean square method. The usefulness of the proposed structure is verified using an example.

In the present paper the response of V transmission line to electromagnetic illumination has been obtained. Also in order to determine the VTL frequency operation band for both TE and TM modes a Gaussian pulse source has been applied to the structure. The VTL structure has received considerable attention in high frequency and microwave IC packaging. The purpose of this study is to determine high frequency design considerations in order to reduce the effects of electromagnetic interference (EMI) on the VTL structure and maintain the desired performance. It was observed that the effect of incident EM waves on the V lines performance is considerably lower than conventional microstrips, however the V lines are more sensitive to sources at close proximity. In addition, although the V lines show lower dispersion at higher frequencies, their frequency operation band is limited by a resonance like behavior which is directly related to the V groove dimensions. The full wave analysis is carried out using the Yee-cell based 2 Dimensional Finite Difference Time Domain method (2D-FDTD), while enforcing a very stable and efficient mesh truncation technique.

Space division multiple access (SDMA) is a promising can- didate for improving channel capacity in future wireless communication systems. Considering that discrimination performance of the user in the spatial domain depends on the array arrangement, and as a result the optimum element arrangement for SDMA should be defined, beam- forming play a very important role providing fundamental theory of design procedure. However the pattern of antenna array is determined by array geometry. Two-dimensional (2-D) spatial filters that can be implemented by microstrip technology are capable of filtering the re- ceived signal in the angular domain as well as the frequency domain. This paper focuses on various geometries of eight and nine elements antenna arrays using circularly patch elements as well as hexagonal ar- ray with seven elements. The network throughput is further analyzed to determine if using a fully adaptive pattern (LMS algorithm gener- ated pattern) results in a higher throughput with or without presence of mutual coupling effects.

The interaction of a helical antenna,moun ted on a mobile handset, with a human head phantom is investigated in this paper. Using the Genetic Algorithms (GA) technique combined with the Method of Moments (MoM), an optimization of the antenna structure is achieved regarding the input impedance at the operating frequency. The Finite Difference Time Domain (FDTD) method is then applied to simulate the handset's function in the close region of a spherical homogeneous and heterogeneous head phantom. A formula, based on an application of an existing model proposed by Kuster and Balzano for dipole antennas,pro vides a rather accurate prediction of the induced Specific Absorption Rate (SAR) values in the human head due to the radiating helical antenna. The concept of relating the SAR to the current on the antenna is used in this study to formulate the final expression. Moreover,using the theory of regression, the results of the calculated peak or average SAR are correlated with the distance between the antenna and phantom and with the standing wave ratio (SWR) at the antenna feed point. Thus,the conception that the SAR is indeed related to the antenna operational parameters is reinforced by the outcome of the current study.

In this paper, a new structure is introduced to design resonators with very short length and without any discontinuity.The introduced structure, called Nonuniform Impedance Resonator (NIR), is an open- or short-circuited Nonuniform Transmission Line (NTL).To synthesize NIRs, strip width or the characteristic impedance function of the microstrip NIRs is expanded in a truncated Fourier series, first. Then, the optimum values of the coefficients of the series are obtained through an optimization approach.The usefulness of the proposed method is verified using some examples.

In [9], scattering problems of plane and beam wave incidences were presented. In that study, it was found that the target configuration together with beam width have a major effect on the laser RCS (LRCS). This conclusion was proved for horizontal incident wave polarization (E-polarization) in free space. The polarization of incident waves is one of the key parameters in the scattering problems and in particular in the resonance region where the target has a comparable size with the wave length. In this work, we extend our study and investigate the impact of vertical incident wave polarization (H-polarization) on the LRCS of large size targets and compare it with RCS of targets with plane wave incidence.

A moment method analysis of a broad wall slot coupled crossed rectangular waveguide junction has been presented in this paper. The coupling slot is longitudinal/transverse and offset from the centre lines of the guides. The integral equations, governing the characteristics of the device, have been obtained using Multiple Cavity Modeling Technique, taking into account of the finite wall thickness and the TE00 mode at the slot apertures and have been solved using Moment Method to obtain the aperture distribution. The normalized resonant lengths/complex S-parameters have been calculated from this field distribution for different guide height/slot offsets/slot widths/slot thickness of the longitudinal/transverse slot over the frequency band. Numerical data, thus obtained, have been compared with measured/literature available/CST Microwave Studio Simulated data. The theory has been validated by the reasonable agreement obtained between them. It has been shown that, neglecting the TE₀₀ mode at the slot apertures can adversely effect the estimation of the resonant frequency and equivalent network parameters.

In many cases it is desired to have both high capacity and small antennas in wireless communication systems. Unfortunately, the antenna performance deteriorates when the antennas get electrically small. In this paper, fundamental limitations from antenna theory and broadband matchingare used to analyze fundamental limitations on the spectral efficiency of an arbitrary antenna inserted inside a sphere.

Cellular communications using high altitude platforms will predominate the existing conventional terrestrial or satellite systems. Radio coverage of HAPs is an important issue that affect the cellular system design, therefore a deep analysis of the HAP cell footprint will be presented in two coverage models and the cell parameters are also deduced for subsequent cellular design. In the design stage, a cell generating algorithm is introduced to define their locations more accurate. When deploying the cellular system with such algorithm, the cells have proper overlap and interspacing.

Cellular communications using high altitude platforms (HAPs) will predominate the existing conventional terrestrial or satellite systems but requires some optimization especially in the cellular radio coverage design. The design of HAPs cellular system suffers from increasing cell area when directing the same beam to cover lower elevation regions and therefore requires some modification in its location. In this paper either spot-beam antennas or antenna phased arrays are used in the radio coverage which are optimized in directing their beams to satisfy mostly uniform cellular layout with minimal coverage problems such as coverage gaps between cells or excessive cells overlap. The cells locations determination is done through proposed algorithm that takes into consideration the cell area increase at lower elevation angles and provides mostly uniform radio coverage especially at the cell edges.