Niksa Burum

Study of Mutual Coupling Between Circular Stacked-Patch Antennas on a Sphere

A rigorous mathematical analysis is given of spherical stacked-patch arrays with emphasis on the physical interpretation of mutual coupling mechanisms present in doubly- curved convex structures. The analysis method is based on electromagnetic field representation in terms of spherical harmonics where each harmonic has the same angular variation as the spectral source component. To obtain the spectral representation the vector-Legendre transformation is applied to currents and fields. A novel approach to the mutual coupling calculation within the method of moments analysis of spherical arrays is applied. By expressing the patch current in terms of two suitable potential-like auxiliary functions, it is possible to avoid the use of Eulers formulas for coordinate system rotation and the related lengthy integrations. Instead, the rotation of antenna elements and corresponding current distributions can be done in closed form with the help of Vilenkins addition theorem for associated Legendre functions. It is shown that the new approach results in significant acceleration and improved accuracy of the analysis of spherical patch antenna arrays. The algorithm is successfully tested against a commercially available electromagnetic software and measurements performed on the developed laboratory model, confirming its accuracy for both input impedance and mutual coupling calculation and with only a small difference between the predicted and measured resonant frequencies, due to limitations in the experimental model. The influence of the structure parameters on mutual coupling level is extensively investigated, including all coupling mechanisms and leakage of energy due to curvature of the structure. It is shown that stacked-patch antennas can have reduced coupling level comparing to single patch antennas with possible deep nulls above the antenna resonant frequency.

Performance Analysis of Spherical Stacked-Patch Antennas

The interest for spherical arrays is based on their possibility to direct single or multiple beams through complete hemisphere. In this article, circular stacked-patch antennas embedded in a multilayer spherical structure are analyzed using the spectral-domain approach and the moment method. The influence of structure radius on input impedance, mutual coupling and radiation pattern is investigated. It is shown that the properties the most affected by the variation of structure radius are the resonant frequency and the mutual coupling level. The results confirm the importance of rigorous analysis of curved patch antennas. Furthermore, a laboratory model is built to validate the developed program. The agreement between measured and calculated results is good

Radiation pattern of spherical array of rectangular microstrip patches

A program for calculating the radiation pattern of spherical arrays consisting of quasi-rectangular patches is presented. The problem is solved in the spectral domain, i.e. for each value of spectral variable only a one-dimensional problem has to be solved. A general algorithm for calculating Greens functions is used in the program, therefore the patches can be printed on or embedded in a multilayer spherical structure. Two different types of array grids are investigated: icosahedron grid and quasi-rectangular grid.

PSO and ACO algorithms applied to location optimization of the WLAN base station

The main goal of this work is to show the use of evolutionary computation techniques. The particle swarm optimization (PSO) and ant colony optimization (ACO) in indoor propagation problem. These algorithms employ different strategies and computational efforts, but also they have something in common. Therefore, it is appropriate to compare their performance with the genetic algorithm (GA). We have demonstrated their ability to optimize base station location using data from neural network model of wireless local area network (WLAN). The results show that PSO has- better properties compared to ACO algorithm. The ACO algorithm needs further work to optimize the algorithm parameters, improve analysis of pheromone data and reduce computation time. However, the ant colony based approach is utilizable for solving such problems.

Moment method analysis of rectangular microstrip antennas on spherical structures

The interest for spherical arrays is based on their possibility to direct single or multiple beams through a complete hemisphere. Arrays of rectangular microstrip patches embedded in a multilayer spherical structure are analyzed using the spectral-domain approach and the moment method. In order to avoid numerical problems a modified vector-Legendre transformation and normalized Legendre polynomials are defined and applied to the solution procedure. The influence of structure radius on the input impedance and the resonant frequency of the spherical rectangular microstrip patch antenna are studied. A laboratory model is built to test different configurations of patches and to validate the calculated results.

A comparison of neural network models for indoor field strength prediction

This paper presents a comparison of the field strength prediction in indoor environments based on ray tracing, multilayer perceptron and radial basis function networks. It has been already shown for neural networks as powerful tool in RF propagation prediction. It is very important to choose proper algorithm for training a neural network, so we compared several training algorithms for the case of multilayer perceptron model. As the case used a corridor of university building in Dubrovnik, for which calculation, simulation and measurement of signal strength were obtained. The results show an improvement in field strength prediction with neural models over conventional models if training algorithm and neural network architecture are carefully chosen. The best results are obtained by the radial basis function neural network model.

Location Optimization of WLAN Access Points Based on a Neural Network Model and Evolutionary Algorithms

In this article we intend to show the use of well-known evolutionary computation techniques—Particle Swarm Optimization (PSO) and Ant Colony Optimization (ACO) - in an indoor propagation problem. Although these algorithms employ different strategies and computational efforts, they also share certain similarities. Their performance is compared with a genetic algorithm (GA), which is used as reference in this case. The ability of these algorithms to optimize access point locations using data derived from the neural network model of a particular Wireless Local Area Network (WLAN) is demonstrated. Better results are obtained by the PSO algorithm compared to the ACO algorithm. Although the ACO algorithm requires further work to optimize its parameters, improve the analysis of pheromone data and reduce computation time, the ant colony-based approach is useful for solving propagation problems.

Input impedance and mutual coupling of spherical rectangular microstrip patch antennas

The input and mutual impedances of rectangular microstrip patches mounted on a spherical structure are studied in the paper. The analysis approach is based on the moment method where the elements of the moment method matrix are calculated in the spectral domain. In order to avoid numerical problems a modified vector-Legendre transformation and normalized Legendre polynomials are defined and applied to the solution procedure. An approximate method is developed to calculate coupling between basis and test functions located on different patches. A laboratory model is built to test different configurations of patches and to validate the calculated results.

Analysis of Spherical Lens Antennas - Comparison of Three Analysis Methods

The paper presents a comparison of three approaches for analyzing spherical lens antennas - spectral-domain method, ray-tracing method, and time- domain finite integration technique (FIT) implemented in commercial software CST Microwave Studioreg. The spectral-domain method takes advantage of transforming the three-dimensional problem into a set of one- dimensional problems. The spherical lens antenna is rigorously taken into account by implementing the Greens functions for the multilayer spherical structures. The ray- tracing method is a general analysis method that can be applied to all kinds of lenses with general (non-symmetric) shape. Finally, FIT implemented in commercial software is general purpose full-wave method. The results of the analysis are compared with measured radiation pattern of a 12 layer Luneburg lens antenna.

Analysis of spherical lens antennas - comparison of two approaches

The paper presents a comparison of two approaches for analyzing spherical lens antennas - spectral-domain method and ray-tracing method. The spectral-domain method takes advantage of transforming the three- dimensional problem into a set of one-dimensional problems. The spherical lens antenna is rigorously taken into account by implementing the Greens functions for the multilayer spherical structures. Different types of feeding antennas can be easily included in the analysis method by calculating the vector-Legendre transformation of the equivalent or physical currents that represent the considered feed. The ray-tracing method is a general analysis method that can be applied to all kinds of lenses with general (non-symmetric) shape. The results of the analysis are compared with measured radiation pattern of a 12 layer Luneburg lens antenna.