Some Techniques Of Smart Antenna Arrays

Smart antenna is known as one of the key techniques in the third generation wireless communication systems. Due to the importance of antenna arrays in smart antenna systems, the study of the array techniques is urgent and important. Associated with three research projects, this work is mainly concerned with array elements, array structure and calculations of array impedances versus operating frequencies. In the dissertation, the author's major contributions are as follows: A new types of array structure, known as circular reflection array, is proposed and studied. A detailed analysis to the new structure with two cases is presented. The radiation patterns of 4-elements and 6-elements circular reflection arrays in different distances between the active element and the passive element, and different length of the passive element are calculated, which shows that the additional passive elements can improve the pattern of the circular array, and decrease the differences between beams, and produce several equal wavebeams. A method known as asymptotic waveform evaluation (AWE) is firstly employed to analyze the array impedances versus the operating frequencies. The input impedances of the array in several different structure are calculated. By using the AWE ,the calculation time is much smaller than that by using MOM. The impedances of the array in different distances between the active element and the passive element and different length of the passive element are calculated and analyzed. The method is efficient and fast in analyzing the wideband characteristics of the arrays. The radiation characteristics of an array with elements in a medium and the radiation space in another medium are studied in detail, and the maximum and minimum radiation conditions are firstly deduced. Finally, the radiation patterns of two kinds of special arrays are presented. A microstrip array is designed to meet the needs of the technical specifications. A hybrid method with the full wave, FFT and biconjugate gradient (BCG) is used to calculate the current distributions on the microstrip. The simulated results show that the method can improve the analysis efficiency and speed up the calculation speed. A hybrid method which combines the MOM with the method of wavelet is used to calculate the current distributions along a wire antenna. By using this method a square loop antenna and a sleeve antenna are analyzed. The simulated results show that the hybrid method is faster than the traditional MOM method.