Study On Miniaturized Helical Antenna System

In recent years, the application of near field communication has become more and more widely. There are some new transmission technology such as RFID and UWB which have higher demands on the antennas. The antennas are required to miniaturize, especially in handheld system.Based on equipment needs, three dual-band antennas are designed: non-equidistant helical antenna, circular ring microstrip ring antenna and ferrite helical antenna. The structure of non-equidistant helical antenna is proposed based on the traditional helical antenna. The size of normal mode helical antenna is very small, so it is a better choice and the simulation results are also very well. In this paper, the size of microstrip antennas are reduced by the load short-circuit point and the slot lines. From the simulation results, load short-circuit point and the slot lines can change the direction of the antenna surface current, so it change to increase the size of the antenna and decrease the resonant frequency about 80MHz, achieving a small size. A set of spiral antenna structure loaded ferrite are proposed in order to make further reduce the size of helix antenna. The magnetic field can be concentrated in the internal helical antenna by using ferrite, which increases the inductance of the coil and reduces the size of helical antenna, then make the size of helical antenna smaller. From the results of simulation, this structure reduces by half the number of laps, well realized miniaturization.Finally, the miniaturized pitch helical antenna and ferrite loaded helical antenna are fabricated, which are measured by the vector network analyzer. A test system is set up to verify the transmission performance of the antennas by transporting square wave signals of different frequency.