Reseach On Tightly Coupled, High Gain Broadband Dipole Antenna Array

Recently, tightly-coupled antenna array has become a hotspot. Compared to the design technology of traditional arrays, which tend to avoid the mutual coupling between antenna units, this method is to make full use of the effects to broaden the impendence bandwidth. Thus, the attenuation of the surface current at the end of the units is under suppression. In addition, dipole is often employed as the unit of arrays, because of its simple structure, good polarization and easy-to-form-array characteristics. Based on the tightly coupled antenna array theory, the related research about the array is developed. The main works of the thesis are as follows:Firstly, the research background and meaning, with the current status of study, are presented. Then, the related theory of arrays and the operating principle of tightly coupled antenna arrays are summarized.Secondly, a wideband dipole with low cross polarization characteristic is designed. Both side of each arm of the dipole is folded. This operation, on the one hand, decreases the physical dimension of the dipole to achieve miniaturization; on the other hand, broaden the bandwidth via the capacitive from the folded parts. Additionally, a microstrip balun structure is presented. Thus, the impendence balance-unbalance transmission is achieved. As a result, the dipole shows a good performance both in impendence and radiation characteristics. The impendence bandwidth reaches 71.78%, the cross polarization is below -20dB, and the average gain obtain 3dB. The measured result matches well with the simulated result.Thirdly, the dipole designed above is employed as the unit of the array. According to the interlacing "Z" shape arrangement, a wideband, tightly-coupled, high gain 4-element array is presented. After adjusting and optimizing the distance of crosswise and endwise between the unit cells, the bandwidth is broadened according to the tightly coupled effects. In order to achieve directional radiation characteristics, an arc shape reflector is designed. The function of the baffler at the upside and downside of the reflector is to decrease the side lobe and back lobe created by the electromagnetic wave diffraction effects. After simulating and optimizing the antenna array model, the results show a good performance. The impendence bandwidth of the array is 85.25%. The main lobe width on the E-plane radiation pattern achieves 20° and the average gain of the array reaches 15dB.