The Design Of Microstrip Antenna And Impedance Matching Networks

With the rapid development of the technology of wireless communication in the whole world, microstrip antenna has been widely used in different fields for it has a lot of merits such as a small volume, light in weight, stabilization in structure, flexible feed manner, easy for batch production.At first, four analysis approaches of microstrip antenna are involved, then radiation principle of rectangular microstrip patch antenna by transmission line model theory which brings the design formula of rectangular microstrip patch antenna. According to the design formula, the initial parameters of 800MHz rectangular microstrip patch antenna are calculated. But there are a little difference between the initial parameters and the real antenna parameters so that the initial parameters should be rectified. The antenna's model is set up in HFSS which is an electromagnetic simulation software. The antenna's radiating character is simulated by HFSS, so we can adjust the antenna's parameters until its radiating character fits in with the designing demands. The antenna's optimization parameters are gained in this way.From the antenna's input impedance simulation chart, its impedance is not consistent with the antenna's feed line characteristic impedance when there are some power reflecting in the termination of feed line, which leads to that the antenna could not gain the most power. In the next process of impedance matching, this paper proposes two methods: Capacitors and Inductors, Microstrip transmission line. The essence of two methods both make use of Smith chart method. ADS - (Advanced Design System) software is applied to design the matching network for the antenna's input impedance. Finally, from the Smith simulation chart in ADS, input impedance is very close to the antenna's feed line's characteristic impedance, as makes the conclusion that the result meets the deigning demands.Finally, two 800MHz rectangular microstrip patch antennas are built as the receiving antenna and transmitting antenna which are used in the Reader and Writer of RFID. The result of practical measurements shows that the antennas have a good feature on radiation distance and radiation lobe.