Magdy F. Iskander

Propagation prediction models for wireless communication systems

A comprehensive review of the propagation prediction models for terrestrial wireless communication systems is presented in this paper. The classic empirical models are briefly described and the focus is placed on the application of ray-tracing techniques to the development of deterministic propagation models. Schemes to increase the computational efficiency and accuracy are discussed. Traditional statistical models are also briefly reviewed for completeness. New challenges to the propagation prediction are described and some new approaches for meeting these challenges are presented.

A Dual-Polarization Slot Antenna Using a Compact CPW Feeding Structure

A dual-polarization coplanar waveguide (CPW)-fed slot antenna is proposed in this letter. By exploiting the even and odd modes of a CPW structure, two orthogonal polarizations can be excited in a slot aperture by the same feeding CPW, which results in a compact dual-polarization antenna design with very good isolation between the ports. The -10-dB reflection coefficient bandwidths of two polarizations are 670 MHz (27.9%) for one polarization and 850 MHz (35.4%) for the other, and the isolation between the two ports in the WLAN band is better than -32.6 dB. The radiation pattern and efficiency of the proposed antenna are also measured, and radiation pattern data are compared with simulation results.

A Compact Hepta-Band Loop-Inverted F Reconfigurable Antenna for Mobile Phone

A folded loop-inverted F reconfigurable antenna for mobile phone applications is designed and the obtained results are discussed in this communication. It is shown that loop antenna mode and an inverted F antenna (IFA) mode are controlled by only one p-i-n diodes with simple bias circuit. The impedance can be matched by adopting a matching bridge for both the loop and IFA modes. In a compact volume of 60 × 5 × 5 mm3, the proposed antenna operates in hepta-band, including GSM850, GSM900, GPS, DCS, PCS, UMTS and WLAN, with the return loss lower than 6 dB. A prototype of the proposed antenna is fabricated, measured, and obtained results including return loss, efficiency and gain, are presented.

A ray-tracing method based on the triangular grid approach and application to propagation prediction in urban environments

This paper presents a fast ray-tracing procedure based on triangular division of the propagation environments. Unlike other accelerating methods that are mostly based on pre-establishment of visibility, this method does not require knowledge of the position information of the base station and/or receiving antennas and is thus more general. Although the triangulation is done in a two-dimensional (2-D) plane, this method is suitable for three-dimensional (3-D) simulations when a proper data structure for buildings is constructed. Validation results show good agreement between calculated and measured data from the European COST 231 project. The improvement in the computational efficiency is clearly demonstrated in examples.

Optical scattering and absorption by branched chains of aerosols

We utilize the Volume Integral Equation Formulation (VIEF) and the method of moments to calculate the electromagnetic scattering and absorption of aerosol particles with branched-chain structures. Two kinds of polarization of the incident electromagnetic wave were considered: the cross- and end-fire polarizations. The numerical results of internal electric field distribution, absorbed power, and extinction and scattering cross sections, obtained from the VIEF, show excellent agreement with the Mie theory for the special case of spherical particles. Comparison between the results of the VIEF and Iterative Extended Boundary Condition Method for very long oriented (elongated) chains of particles also showed good agreement. After validating the accuracy of the VIEF, the absorption characteristics of three branched-chain structuressimulated from microscopic pictures of coagulated smoke aerosol particles were calculated. Results showed that the ratio of absorption in the two polarization cases, P(cross-fire)/P(end-fire), for very long oriented chain structures is as high as a factor of 4 at lower frequencies (lambda =10microm). While in the higher frequency (lambda = 0.5-microm) case, the ratio Of P(cross-fire)/P(end-fire) is reduced to 2.0. For branched-chain structures, the ratio Of P(cross-fire)/P(end-fire) decreased with the increase in the number of the side branches. These observations show that the frequency, polarization, and structure factors play important roles in determining the optical characteristics of branched chains of aerosol particles.

A new procedure for improving the solution stability and extending the frequency range of the EBCM

The extended boundary condition method (EBCM) has been frequently used to obtain the absorption and scattering characteristics of axisymmetric dielectric objects. For applications involving relatively high-loss dielectric objects, however, the method was usable only at frequencies below resonance. In this paper a new procedure for improving the stability and extending the frequency range of the EBCM is presented. This new procedure has two main features: 1) it is iterative, since it starts with a known solution that approximates the scattering problem, and 2) it involves separate field expansions in each of the overlapping subregions which describe the total interior volume of the object. For example, for high-loss dielectric objects, such as the biological models of humans and animals, the first step in the procedure is to replace the lossy dielectric object with a perfectly conducting one of the same shape and solving the scattering problem to determine the current density on the surface of the conductor. This surface current is then used to calculate the induced field expansions inside the dielectric object. It is shown that the numerical stability of the solution is further improved by dividing the interior region of the object into overlapping subregions, in each of which a separate field expansion is assumed. The electric and magnetic surface currents so obtained from the solution of the internal problem are then used to improve the initial estimate of the current density on the surface of the object. The iterative procedure continues until convergent values of the surface currents and the fields are obtained. Numerical results illustrating the improved stability of the iterative EBCM (IEBCM) solution at higher frequencies as well as its accuracy in calculating the absorption characteristics of a spheroidal model of man in the resonance and the postresonance frequency range are presented.

Dual-band WLAN dipole antenna using an internal matching circuit

A dual-band dipole antenna for wireless local area network (WLAN) is designed and experimentally tested at both the 2.4 and 5 GHz (IEEE 802.11b/g and 802.11a) WLAN bands. The design procedure involves obtaining a full resonance frequency in the 2.4 GHz band and then using a matching network to achieve a secondary resonance at the 5 GHz band. It is shown that by correctly designing the dipole, the matching network can be simplified to only one series inductor. The design was experimentally verified by constructing a dipole on a FR4 board (12 mm*45 mm*0.45 mm) and measuring its input impedance and the radiation characteristics at both bands. The measured VSWR 2:1 bandwidth in the 2.4 GHz band is 710 MHz, and the bandwidth in 5 GHz band is wider than 1 GHz. The VSWR 3:1 bandwidth is more than 3.6 GHz and it covers from 2.32 GHz to above 6 GHz. It is significant that the designed dual-band dipole maintained good radiation efficiency values at both bands. Specifically, and based on the measured radiation patterns, an efficiency value of 85% /spl sim/ 87% is obtained at 2.4 GHz and a value in the range of 55 /spl sim/ 64% is obtained in 5 GHz band.

16-term error model and calibration procedure for on wafer network analysis measurements (MMICs)

Vector network measurements are enhanced by calibrating the measurement system over the entire band of interest. This is done using a 12-term error correction model. Many measurement systems, including open air devices such as MMIC wafer probes, contain leakage and coupling error terms not modeled in current calibration systems. All error terms in such a system are included in a new 16-term error model and calibration procedure. Corrected measurements using the 16-term calibration procedure are compared with thru-reflect-line (TRL) and 12-term calibration measurements, and excellent agreement is observed for a nonleaky system. For a leaky system, the 12-term model is shown to break down, while the 16-term model retains its accuracy. The results validate the accuracy and viability of the calibration procedure for MMIC wafer probe measurements and other measurement systems containing leakage. >

Comparative study of high-performance GPS receiving antenna designs

A major factor in the performance of a differential Global Positioning System (DGPS) ground station is the performance of the antenna. The article analyzes and compares the performance of different GPS antenna designs. The specifications for the DGPS ground station antenna include hemispherical coverage and good multipath rejection. Good multipath rejection can be achieved by using an antenna that presents circular polarization and sharp drop-off at low elevation angles. In more detail, the specifications for the high precision GPS antenna include right hand circular polarization with a minimum of 15 dB of cross polarization rejection, hemispherical coverage presenting a variation of less than 3 dB over the main beam and a drop-off rate larger than 1 dB/deg for elevation angles from -5 to 5 deg. These specifications should be satisfied at the frequencies of 1.227 GHz and 1.575 GHz. The antenna designs examined in our study include patch antennas, helical antennas and conical spiral antennas. The numerical results from a successful conical spiral antenna design were verified experimentally.

Design optimization of interstitial antennas

The radiation characteristics of multisection insulated antennas in conductive tissue are discussed. The effects of varying the diameters and lengths of the center conductors in the various sections of the antenna and the diameter and type of the insulation on the electromagnetic power deposition pattern and input impedance characteristics were examined. An approximate numerical model which calculates the current distribution and the radiation characteristics of multisection insulated antennas was developed. The numerical predictions were verified in a qualitative way experimentally by mapping the various near- and far-field components of the antennas. On the basis of these results, design tradeoffs are identified and quantified and guidelines for optimum designs are specified. In particular, it is shown that an insulation-to-center-conductor diameter ratio between 1.5 to 2.0 is optimum for uniform Teflon insulation, and that a multisection arrangement with the thinnest insulation near the antenna tip has superior performance compared with the uniform-insulation or other multisection designs.<<ETX>>