Tham khảo tài liệu 'advances in satellite communications part 2', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 4 Advances in Satellite Communications Although an analytical approach can sometimes provide a fast approximation of helix radiation properties Maclean Kouyoumjian 1959 generally it is a very complicated procedure for an engineer to apply efficiently and promptly to the specified helical antenna design. Therefore we combine the analytical with the numerical approach i. e. the thorough understanding of the wave propagation on helix structure with an efficient calculation tool in order to obtain the best method for analyzing the helical antenna. In this chapter a theoretical analysis of monofilar helical antenna is given based on the tape helix model and the antenna array theory. Some methods of changing and improving the monofilar helical radiation characteristics are presented as well as the impact of dielectric materials on helical antenna radiation pattern. Additionally backfire radiation mode formed by different sizes of a ground reflector is presented. The next part is dealing with theoretical description of bifilar and quadrifilar helices which is followed by some practical examples of these antennas and matching solutions. The chapter is concluded with the comparison of these antennas and their application in satellite communications. 2. Monofilar helical antennas The helical antenna was invented by Kraus in 1946 whose work provided semi-empirical design formulas for input impedance bandwidth main beam shape gain and axial ratio based on a large number of measurements and the antenna array theory. In addition the approximate graphical solution in Maclean Kouyoumjian 1959 offers a rough but also a fast estimation of helical antenna bandwidth in axial radiation mode. The conclusions in Djordjevic et al. 2006 established optimum parameters for helical antenna design and revealed the influence of the wire radius on antenna radiation properties. The optimization of a helical antenna design was accomplished by a great number of computations of various antenna .
