Study On The Microstrip Array At The Ku Frequency Band

Dual-polarized microstrip antennas not only have the advantages of low profile, low cost and mass production, but also can maximize the received signal and reduce the detrimental effects caused by the multi-path fading. Antennas with dual-polarization can be widely applied in satellite communications systems and mobile communication systems, and they have important theoretical meaning and practical application value.The basic theory of the microstrip antenna, methods of realizing dual-polarized antenna, analyzing and synthesizing the circular loop array antenna, designing microstrip feeding networks, related measured results and improvement of the feeding structure are studied in this paper. The primary contribution is as follow:1. The theory analytical models of microstrip antenna, transmission line and cavity model are described. Based on these methods, dual-polarized microstrip antennas, improved feeding methods and other dipole-like dual-polarized antennas are proposed. And the antennas with bi-directional radiation applied in WLAN systems are also presented. Single and multiple concentric-ring-array-antenna, meanwhile, the circular aperture are analyzed. In order to realize the low side-lobe in array antenna, taylor distribution is adopted. By using the coding and computing software Matlab, high gain and low side-lobe array antenna is synthesized.2. The feeding network and sum-difference device of monopole radar microstrip array antenna are analyzed and designed in detail with parallel and series structure. The related passive devices such as loop coupler, branched directional coupler, Wilkins power divider and series connection branch are designed. Appling these practical methods, dual-polarized microstrip array of eight loops is designed accordingly, and simulated results are also obtained. The proposed eight loops dual-polarized microstrip array antenna is fabricated and measured. The measured results are mainly included S parameters of every port and the radiation patterns of sum and difference.3. On the basis of measured results, the array shows the disadvantages of low gain and asymmetrical radiation patterns. To find the reasons, the further researching work is carried out. In the end, radial waveguide feeding structure is proposed to improve the shortcomings of low efficiency and high insertion loss of the microstrip line or stripline. Based on the design methods of planar radial waveguide array, coupling probe-fed microstrip antennas of four and eight circles are proposed for linear polarization. Simulated results show that the radial waveguide can minimize insertion loss of the feeding network effectively.