Out of band antenna characterization.
Date of Issue2014
School of Electrical and Electronic Engineering
The aim of this project is to study the out-of-band performances of the antennas and from there, understand the electromagnetic compatibility of different systems when working together in this electromagnetic rich environment. During the preparation of this research project, the structural parameters, performance characteristics and antenna measurement theory has been studied. Literature review on antenna out-of-band characteristics and electromagnetic compatibility has been done as the references of this research work. The airborne L, S, and C band blade antennas are the objects of research of this project. The blade antennas are all monopole antennas which consist of an RF port at the bottom, a metal radiator, a Teflon cylinder load and a dielectric radome covering the antenna. The dielectric radome is found to change the omni-directional monopole antenna into a directional aircraft blade antenna. The pattern measurement on the blade antennas is done to obtain the far-field radiation pattern measurement. Simulation results of the L, S and C band blade antennas are well matched with the anechoic chamber measurement data. It was found that the blade antennas have both in-band frequencies and higher out-of-band frequencies. Gain and radiation pattern of the blade antennas are found to be influenced by the ground plane and dielectric radome in a way that the blade antennas have two main lobes in the forward and backward directions of the antenna at most of the frequencies. Equations were built for each antenna to illustrate the relationship between their dimensions and the in-band and out-of-band resonant frequencies. Based on the individual equations, a general equation was derived to predict the out-of-band resonant frequencies with known dimensions of the blade antennas. This will provide a good reference for future blade antenna design in consideration of avoiding electromagnetic interference at out-of-band frequencies. Except the relationship between antenna dimensions and the resonant frequency, the maximum gain of the blade antennas at frequencies below 1GHz was found to increase with the frequency by 40dB per decade. A general prediction model has been developed to describe the maximum gain of the blade antenna from the lower out-of-band frequency up to higher out-of-band frequency. The effects of the dimensional parameters including the antenna length, Teflon cylinder load length, Teflon cylinder load position and the dielectric radome height are investigated as the last part of this research. The impacts of these parameters on the resonant frequency have been studied. Based on the investigations on individual parameters, the resonant frequency equation has been derived to characterize the frequency performance of the blade antennas and reduce the effort in testing simulation models. At the end of this thesis, recommendations have been made to suggest that more considerations should be put into the relationship between the dimensional parameters and the out-of-band frequency of the blade antennas. It is found that the antenna gain varies sinusoidally with the length of the Teflon cylinder load. However, it is suggested that the relationship between the dimensions and the antenna gain should be studied based on the in-band relationship. At last, although the resources may be limited, it is suggested that the future research in antenna, electromagnetic compatibility and interference should be based on both simulation and measurement in real scenario to obtain better results.
DRNTU::Engineering::Electrical and electronic engineering