Erdem Yazgan

New computation of the resonant frequency of a tunable equilateral triangular microstrip patch

A new dynamic permittivity expression is formulated to be used in the cavity analysis to determine the resonant frequency of an equilateral triangular microstrip patch. The proper sidelength extension expressions are given for low and high substrate permittivity cases. Better accuracy with respect to the moment method and other previous models is obtained for various structural parameters and operational modes. The proposed computation is also extended for the analysis of the two-layer structure in order to determine the air-gap tuning effect on the resonant frequency.

Characteristics of a circular patch microstrip antenna on uniaxially anisotropic substrate

Resonant characteristics of a circular patch microstrip antenna on the uniaxially anisotropic substrate are determined via spectral domain analysis. Greens functions of the structure in Hankel transform domain are determined by using Hertz vector formulation. The variations in the resonant characteristics depending on the replacement of the isotropic substrate with the uniaxially anisotropic one are analyzed for different permittivity tensor element cases. The results of the study indicate that resonant frequency and bandwidth characteristics of the antenna can be considerably changed due to proper selection of substrate anisotropy ratio and other structural parameters. Depending on the arrived results, operational performance of the antenna will be improved in future studies.

Pattern optimization of a reflector antenna with planar-array feeds and cluster feeds

We study pattern optimization of a parabolic reflector with planar-array feeds and cluster feeds. The optimization is carried out within the conjugate gradient method (CGM) in which the optimum weight vector of a linearly constrained minimum variance (LCMV) beam former is used as the initial condition. Optimization with the CGM to determine element weights is found to yield better sidelobe suppression and true settlement of desired scan direction compared to the LCMV beam former and conjugate field matching (CFM) techniques for the continuous beam-scanning case. The proposed method is also applied to multibeam reflector-antenna design.

Resonant frequency of an air gap tuned circular disc microstrip antenna

In this study, the formulation and the computation of the resonant frequency of an air gap tuned circular disc microstrip antenna are simplified, with improved accuracy, by using a new and very simple effective permittivity expression which is valid for thin and thick gaps. Very good agreement between the theoretical and the experimental resonant frequency values is obtained for the various structural parameters and operational modes.

Compact space-multimode diversity stacked circular microstrip antenna array for 802.11n MIMO-OFDM WLANs

The support of MIMO communication in OFDM-WLAN systems conforming to IEEE 802.11n standard requires the design and use of compact antennas and arrays with low correlation ports. In this paper, the design and analysis of a compact space-multimode diversity provisioning stacked circular microstrip patch uniform linear antenna array (SCP-ULA) for MIMO-OFDM WLAN systems and the associated spatial and modal correlation, ergodic spectral efficiency and compactness gains with respect to dipole (DP-ULA) and circular microstrip patch uniform linear arrays (CP-ULA) with dominant-mode operation are presented.

Limit and application range of the slope-diffraction method for wireless communications

We investigate the limitations on the use of the uniform theory of diffraction (UTD) slope-diffraction method for propagation past knife edges. The settled field that is diffracted past rows of buildings, as computed by numerical integration, has the characteristics of amplitude and phase variation with a scale length that is large compared to the wavelength and has small amplitude near the edges. Using this field, it is shown that the error in the UTD slope-diffraction method for diffraction past a final screen is connected with the Fresnel width, as compared to the scale length of the settled field.

MODELLING OF SHADOWING LOSS DUE TO HUGE NON-POLYGONAL STRUCTURES IN URBAN RADIO PROPAGATION

AtilimUniversityDepartmentofElectricalandElectronicsEngineeringIncek,Ankara,TurkeyE. YazganHacettepeUniversityDepartmentofElectricalandElectronicsEngineeringBeytepe,Ankara,TurkeyAbstract—Raytracingalgorithmsrelyontwodimensionalorthreedimensional database. They use ray optical techniques referred toas the uniform theory of diffraction (UTD) using building databasegivenaspolygons. Buildinggeometriescanalsobemodelledashavingnon-planar geometries, and this would be important in modeling ofshadowinglossduetocurvedstructuresinurbanradiopropagation.To demonstrate modelling of buildings as non-polygonal geometries,a particular building composition involving 3D cruved geometries ischosen, and shadowing loss for this building composition is studiedvia UTD ray tracing. Building structure considered in this studyinvolves main canonical shapes of non-planar geometries includingcone,cylinderandsphere. Singleandmultipleinteractionofsurfacediffractions,effectofcreepingwavesaretakeninto considerationintheanalysis.

Analysis of Annular Ring Microstrip Patch on Uniaxial Medium via Hankel Transform Domain Immittance Approach

In this study, resonant frequency of annular-ring mi- crostrip patch on uniaxial medium is determined using equivalent mod- els of the structure obtained in Hankel Transform Domain depending on TE and TM mode decomposition. For the simpliflcation of the tensor form formulations, equivalent matrix operators are deflned in cylindrical coordinates instead of the difierential ones. Then, eigen- value problem is solved by the application of the moment method and obtained resonant frequency characteristics are compared with that of the isotropic case for difierent anisotropy ratio values and structural parameters. Equivalent circuit models for the structure having mul- tilayered substrates and superstrates are given in order to be used in the following studies on uniaxially anisotropic circular type microstrip patches.

UTD-based propagation model for the path loss characteristics of cellular mobile communications system

This work presents a UTD-based path loss model for cellular mobile communications system in an urban environment. The model considers multiple building diffraction occurring in cellular environments outside the high-rise urban core. Using a UTD wedge diffraction model, the roofs of the successive building blocks are simulated by finitely conducting wedges so that material properties of the buildings are included.

Bandwidth widening in an annular ring microstrip antennas with superstrate

A theoretical and numerical analysis of an annular ring microstrip antennas with superstrate is performed in order to obtain a wider bandwidth operation. At the same time the complex resonant frequency of the structure is determined. The study is performed by using a full wave analysis and Galerkins moment method in Hankel transform domain by taking surface wave contributions into account. The possibility of achieving larger bandwidth operation with TM/sub 11/ mode which originally shows narrow bandwidth characteristics in single layer annular ring antenna is investigated. Numerical results for different antenna parameters are given. The results indicate that the resonant frequency decreases with increasing superstrate thickness and the bandwidth increases for increasing superstrate dielectric constant values.