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.

Smart Antenna system analysis presented with multipath and null constraint for reducing interference and efficient use of spectrum with the help of LMS algorithm for GPS (Global Positioning System) System. A new simple DOA (Direction of Arrival) estimation method by rotation of antenna plane proposed. Simulated Result obtained using MATLABTM.

Stacked microstrip antennas deserve special attention due to their advantageous properties like dual frequency operation and wide bandwidth. In the present communication a theoretical model for single stacked microstrip disc antenna is proposed using extended cavity model. The method of analysis by this model is easier and intuitive than the full wave analysis. Single stacked microstrip disc antenna with co-axial feed locations at different radial positions is analyzed with this model taking different ratios of patch sizes. Antenna properties like return loss, input impedance, gain and radiation efficiency are calculated with the proposed model different cases and compared with the simulated and experimental results. The results are in fairly good agreement.

In this paper we propose a new method to enhance the gain of rectangular waveguide antenna arrays using the double negative medium (DNG) structure composed of strip wires (SW) and split ring resonators (SRR). The electromagnetic parameters of the DNG structure are retrieved and the rectangular waveguide antennas with and without the DNG structure are studied using numerical simulation method. The simulation results show that the DNG structure can congregate the radiation energy when the index of refraction approximates zero,since that the gain of the antenna arrays is enhanced and the radiation performance of the antenna arrays is effectively improved. Far-field radiation patterns are measured, which indicate that this method is effective to enhance the gain.

In this paper an edge coupled microstrip coupler with defected ground structure is presented. A normally 7 dB coupler designed on Alumina substrate is converted into a 3 dB coupler by cutting single rectangular slot in the ground plane encompassing the two transmission lines. Other properties of backward wave coupler remain the same, except for a tighter coupling. With this method of design optimization, it will be possible to fabricate a 3 dB coupler in compact form without strain in fabrication process. The structure is analyzed considering magnetic and electric coupling between the two transmission lines. Simulation based studies show reasonable agreement between analytical results and corresponding simulation results.

In this paper a simple model has been introduced to simulate the propagation of signal in a so called edged microstrip transmission line (EMTL). EMTL is a transmission line in which the signal strip is laid on the edge of the structure (Fig. 1). First a simple structure of EMTL is modeled with an ordinary MTL with improved per unit length inductances and capacitances, and an additional resistance to represent the radiation from the edges. This method is then applied to model a multilayer cross orthogonal EMTL structure as shown in Fig. 2. The model is finally validated using full wave analysis simulator, HFSS. The S-parameters of our model show good agreement with the results of the full wave analysis (HFSS) up to some GHz.

This paper presents an effective medium approach to calculate the attenuation and phase constants of modes in a 3D connected wire medium both below and above the plasma frequency. Physical and nonphysical modes in the structure are identified for all the important lattice directions. According to this, the medium behaves as an isotropic material in the vicinity of the plasma frequency. These results were compared with the numerical simulation and it was observed that the wave spreads below the plasma frequency along all the important lattice directions with the same attenuation constant. This implies isotropic behavior of the 3D wire lattice below the plasma frequency, and thus this medium can be considered as an isotropic negative permittivity medium.

Standard spectral-domain method (SDM) is one of the popular approaches to analyze frequency selective surfaces (FSS). However, it is inherently incapable of handling normal incidence because of its dubious definition of excitation fields, reflection and transmission coefficients using z-component of vector potentials. Moreover, as far as the author knows, it has never been applied to analyze FSS with gangbuster arrays. In this paper, an improved SDM, the vector spectral-domain method, is presented. By proving the equivalence of the spectra of unit cell current and element current, the scattered field from FSS structures is formulated in terms of spectraldomain element current instead of spectral-domain unit cell current. Galerkin's method is applied to obtain the unknown induced surface current. Well-established definition of excitation fields, reflection and transmission coefficients is adopted. Extensive experimental validation has been conducted.

Concentric circular antenna array (CCAA) has interesting features over other array configurations.A uniform arrangement of elements is assumed where the interelement spacing is kept almost half of the wavelength and the array parameters such as the steering matrix and gain are determined.The array performance such as beam power pattern, sidelobe level and beamwidth are discussed in two cases of central element feeding.The two cases are compared showing the reduction in the sidelobe level to more than 20 dB in the case of central element feeding without extra signal processing especially for smallsized arrays that have smaller number of elements and rings.

A rigorous semi-analytical solution is presented for electromagnetic scattering from an array of circular cylinders due to an obliquely incident plane wave. The cylinders are illuminated by either TMz or TEz incident plane wave. The solution is based on the application of the boundary conditions on the surface of each cylinder in terms of the local coordinate system of each individual cylinder. The principle of equal volume model is used to represent cylindrical cross-sections by an array of circular cylinders for both dielectric and conductor cases in order to proof the validity of the presented technique.