Essam E. Hassan

Field solution and propagation characteristics of monofilar-bifilar modes of axially slotted coaxial cable

The electromagnetic problem of an infinite, axially slotted coaxial cable is solved. The monofilar and bifilar eigenmodes are obtained with good accuracy and previous conflicting results are discussed. Further, a field solution satisfying the proper boundary conditions is obtained and shown to be essentially azimuthal. >

Field Solution, Polarization, and Eigenmodes of Shielded Microstrip Transmission Line

Application of the reciprocity theorem leads to a variational expression for the propagation constant of the fields inside shielded microstrip-like transmission lines. The resulting equation involves both the propagation constant and the tangential fields at the air-dielectric interface. Using the Rayleigh-Ritz optimization technique, both the propagation constant and the fields are completely determined. The calculated results of the propagation constant compare well with other available data. Moreover, the field solution obtained is presented in the form of a polarization ratio relating the axial to the transverse electric field. Results cover both low and high frequencies, and the technique proves valid at both frequency ranges. The method may be extended to other configurations of planar striplines by proper adjustment of the integration limits.

Simplified expression for the expected error span recovery for variable length codes

An expression in the form of a series expansion for the error span recovery for variable length codes is presented. Numerical results for both the error span recovery and its standard deviation show complete agreement with those obtained via the complex exact functions. The expression is simple and can be applied to any model where the exact expression is prohibitively complicated.

Sidelobes Level Reduction Using Spatial Optimization of the Array Factor

A new technique based on the analogy between the transfer function of the digital filter used in Sigma-Delta modulation and the target array factor of an antenna array is attempted. The technique is based on optimizing the array factor within the finite angle of the main lobe using direct power minimization outside this lobe. The method achieves better results when compared to a number of optimization techniques available in the literature. Some of the theoretical results are simulated using FEKO commercial software with results compared well to the theoretical findings.

Multiple scattering of plane electromagnetic waves by two dielectric coated conducting strips

This paper describes the scattered field from two dielectric coated conducting strips. The electric and magnetic fields are described here as solutions of Helmholtz wave equation of unknown coefficient in each region due to a plane wave incidence. The unknown coefficient can be obtained by enforcing the boundary conditions. The application of the boundary condition requires the use of the addition theorem of Mathieu function. Results obtained for this problem of along with applications will be presented in the conference.

Time domain energy maximization of the Nyquist pulse shape

Abstract A simple solution to the problem of designing a Nyquist pulse shape with maximum energy within any particular period in the signal impulse response is presented. Such design is important in minimizing timing error at the sampling time in the receiver. Further, the problem of controlling the frequency response pattern of the pulse to conform with specific requirements is solved and an example of emphasizing the high frequency contents is given.

3D Beam Scan Using Ferrite Loaded Circular Waveguide Antenna

Phased or parasitic array antennas with complex feed mechanism are widely used to realize beam scanning. This letter presents a simple magnetized ferrite-loaded circular waveguide antenna with three-dimensional (3-D) scan characteristics. Professional software is used to optimize the dimension and biasing requirement of the antenna. The required magnetizing fields (H0) are tabulated to realize 60° of maximum beam scan in elevation plane for eight different azimuth regions covering 360°. A prototype of the high-power waveguide antenna is fabricated to experimentally verify some of the simulated scan characteristics. Using LTCC technique, embedding the biasing coils within the ferrite cylinder can considerably reduce the H0 values needed for 3-D beam scan.

Exact and numerical solutions for the radiation from slotted cylinder embedded in cylindrical capped corner reflector

A corner reflector antenna, fed through slotted cylinder Embedded in caped corner reflector is considered. An exact solution to a two dimensional problem is developed using the modal expansion solution for TM case. Also, an integral equation is formulated for the current distribution on slotted cylinder and the reflector surface. The moment method is used to obtain the current distribution on the antenna conducting surfaces. The radiation pattern of the antenna is then calculated using both methods for different corner angles. The exact solution considers infinite reflector surface while the numerical solution consider it finite.

A novel mathematical model for complex humidity profile variation with elevation

Free space propagation of communication signals under anomalous weather conditions is unpredicted and may result in very strong signals at certain locations and almost complete blackout at others. This is due to the abnormal refractive index prevailing in the area as a result of the variation of the humidity levels with altitude. In this paper, existing models describing the variations of the humidity profile with altitude which are crucial in predicting the signal strength in space are presented and discussed. It is shown that these models cannot properly describe complex profiles such as those prevailing in high humidity areas like the Caribbean or the Arabian Gulf area. A new mathematical model is suggested to meet the needs for such complex profiles and it is shown that this new model is capable of representing any natural humidity profile accurately without creating false inversion layers as is the case with other models. The new model is applied to the problem of space wave propagation and locations of field strength and weakness are identified.

Radiation from Axial Slot on an Infinitely Long Conducting Circular Cylinder Eccentrically Coated with Dielectric and Partly Embedded in a Ground Plane

An analytical formulation is developed for an axial slot on an inflnitely long conducting circular cylinder eccentrically coated with dielectric and partially embedded in a ground plane. A computer program has been developed based on the resulting formulation. The problem is highly signiflcant since the ground plane could be the body of an aircraft, a ship, or any other mobile system. The efiect of the ground plane can be used to enhance the radiation characteristics in some cases. It is also a support for the antenna instead of using other mechanical mounting supporting system. Numerical results for difierent antenna conflgurations are illustrated. The results show that how one may shape the pattern by ofisetting the slotted cylinder from the center of the dielectric coating.