Design Of Antenna Array Based On The Tightly Coupled Structure

The tightly coupled antenna array is a current research focus. Compared with the traditional design process of antenna array, in which the mutual coupling between the antenna elements is considered as a negative factor, the tightly coupled antenna array utilizes the mutual coupling to extremely broaden the frequency bandwidth and reduce the profile height. However, in practical engineering applications, the truncation effect and the design of feeding balun are two bottlenecks, which limit the frequency bandwidth of the tightly coupled antenna array to be further broadened. Aim at the two problems above, in this thesis the related studies on tightly coupled antenna array are developed. The main work of this thesis includes the following sections:1. The truncation effect to finite tightly coupled antenna array, especially to the array with a small number of elements is studied. First of all, through the study of existing structures, the double-sided printed dipole with overlapping end between adjacent elements is designed as the element of tightly coupled antenna array, and a superstrate is introduced to further broaden the frequency bandwidth. Then an analysis of truncation effect to the designed finite tightly coupled antenna array with 6 ′6 elements is given by the methods of finite array and semi-infinite array. The results show that the E-plane truncation effect mainly affects the impedance characteristics in the low-frequency band of the array. To compensate the truncation effect which deteriorates the performance of antenna array, two methods of termination are proposed. By the use of appropriate termination, the caused impedance mismatch is alleviated and the antenna array can work at the frequency band from 200 MHz to 500 MHz, while the profile height is only 0.15 times of the maximum wavelength.2. A feeding balun structure which is used for the tightly coupled antenna array is designed. By the analysis and simulation of different balun structures, we find it is difficult to transform the impedance from 50 ohm to 200 ohm with a low-profile height balun in the band from 200 MHz to 500 MHz. Therefore, a CPW to parallel two-wire line transition structure with Chebyshev impedance transformer is proposed to achieve the transformation from the 50 ohm unbalanced end to the 100 ohm balanced end. Then, the adjacent antenna elements are parallel fed with the parallel two-wire line structure.Eventually, the impedance transformation from 50 ohm to 200 ohm is realized with the profile height only 0.11 times of maximum wavelength.