Victor G. Kononov

Analysis, Simulation and Measurements of CBS Antennas Loaded With Non-Uniformly Biased Ferrite Material

When ferrite materials are used in the design of the CBS antennas, they are usually magnetized by the applied magnetic field produced by an electromagnet or permanent magnets. In modeling of such antennas, it is common practice to ignore the actual distribution of the applied field and assume it is uniform. We demonstrate that such an assumption leads to inaccurate results when the applied field is severely non-uniform. In contrast to the previous formulations, a formulation presented here leads to accurate modeling and simulated results compare very well with measurement for both uniform and non-uniform field distributions. The utility of the proposed approach is especially evident for the case when the applied magnetic field is severely non-uniform.

Non-Uniform Field Modeling of Ferrite-Loaded Cavity-Backed Slot Antennas

This communication presents a method that accurately models the non-uniformities of the magnetic field present within the ferrite material that is subjected to an externally applied magnetic field. Two major factors that influence this field are the applied magnetic field and the demagnetizing factor. Most of the formulations reported prior to this work ignored the non-uniformity of the applied magnetic field by assuming that this field is constant and unidirectional everywhere in the cavity. In addition to this, the demagnetizing factor was also assumed to be either of the ballistic or diagonal form. The approach presented here removes both of these approximations by determining the nonuniform field distribution using the finite element method and considering the full tensorial form of the demagnetizing factor. Predictions based on the approach presented here are compared with measurements and previous data predicted based on the uniform applied magnetic field along with the ballistic form of the demagnetizing factor.

Exponentially tapered helical antennas

This paper takes the idea of structure tapering and investigates the general effect of such tapering on the performance characteristics of the antenna. In particular, the effect of height, apex radius, and degree of exponential tapering on ellipticity, cross polarization rejection, and reflection coefficient is investigated.

The Impact of Non-Uniform Bias Field on the Radiation Patterns of Ferrite-Loaded CBS Antennas

Modeling of ferrite-loaded CBS antennas often makes use of the simplifying assumptions which involve some kind of averaging of the magnetic bias field. Simulations and measurements presented here demonstrate that failure to account for the non-uniform magnitude, as well as direction, of the bias field leads to inaccurate predictions of not only the input impedance, but also of the amplitude radiation patterns.

Field distribution modeling and measurements of ferrite-loaded CBS antennas

When computing the permeability tensor of the ferrite material, it is often assumed that the internal magnetic field is uniform. In this paper we compare simulations and measurements of the input impedance of a ferrite-loaded CBS antenna based on the non-uniform field distribution with those based on the uniform field distribution.

Multipath scattering by cylinders and spheres

Scattering problems with multiple canonical scatterers, like cylinders and spheres, may be modeled by utilizing the orders-of-scattering approach. This method provides an exact solution; however, being iterative in nature, the accuracy of the solution depends on the number of iterations; in other words, the number of higher-order scattered fields taken into account. The orders-of-scattering solutions were compared against the numerical solutions, obtained using a commercial software such as WIPL-D, and an excellent agreement is indicated. This technique has a potential for modeling dynamic multipath environments of multiple scatterers, such as those found in wireless communication environments, provided that the environment can be approximated by objects of canonical shape. The obtained results can then be compared with statistical models to shed more physical insight into the scattering process.

Magnetic field modeling of a reconfigurable cavity-backed slot antenna

This paper investigates the nonuniformity of the applied magnetic field and presents the comparison between the measured field, finite element method data, and the analytical formulation obtained by solving Biot-Savarts equation.

Wideband, multi-frequency ferrite-loaded CBS antennas with non-uniform bias

Simulations and measurements of the input impedances and radiation patterns clearly demonstrate that approximating a severely non-uniform internal magnetic field with the uniform distribution is unacceptable and it leads to very inaccurate predictions. On the other hand, the Non-uniform approach, which does not perform such averaging, yields very accurate predictions, especially when compared with measurements. In addition, it is shown that if some of the significant components of the internal magnetic field are omitted, the predictions become very inaccurate and do not compare well with measurements.

Multipath modeling using canonical scatterers

Multipath modeling is presented using infinitely long cylinders. It is shown that the known stochastic fading models, Rayleigh and Rician, can be obtained by treating multipath deterministically, that is, by solving the electromagnetic scattering problem.

Analysis and Simulation of the Propagation Channel Complexity on Signal Fading

Radio propagation environment with scatterers restricted to the far-zone is analyzed to demonstrate how signal fading is affected by the complexity of the environment. To simulate signal fading, an approximate model based on infinite perfectly conducting (PEC) cylindrical scatterers is used and simulated. Depending on the scattering environment, the simulated data match the classical models of Extreme value, Gamma, Rayleigh, and Generalized Gamma.