Design Of Low Profile High-gain Circularly Polarized Array Antenna

Through analyzing the development of the antenna in the wireless communication, this paper recognizes that possesses the radiation property of high-gain, circular polarization has become a trend. Focusing on two of the most widely used antennas- helical antenna and microstrip antenna, we elaborate their basic theory, advantages and disadvantages.Afterwards, two array antennas-4 units helical antenna arrays and 12 units microstrip antenna arrays which have character of low profile, high gain, better circular polarization performance is proposed for S-band. Main contents details as follows:Firstly, using the good characteristics of the axial mode, a 4 units helical array antenna is designed according to the proposed design requirements. In the design process, its low profile is achieved by using short helical antenna, the array adopt a 1×4 structure to solve the problem which the existing helical arrays have larger size. In order to optimize the circular polarization of the array, the units are rotated placement and were fed with incentive which equal in amplitude and difference of 90? in phase. Then the array antenna is fabricated and tested, the results show that in the desired band, the array have the features of VSWR <1.5, AR <2d B, axial gain greater than 12 d Bi, the size of350mm×100mm×30mm, simulation and physical tests meet the design requirements.Secondly, a 12 elements microstrip array antenna is also proposed in this paper. Its design requirements are that VSWR <2, AR <3d B, axial gain is greater than 13 d Bi in the operating band of 1980-2200 MHz and design size is 380mm×280mm×15mm. By analyzing the design requirements, its low-profile feature is ensured by employing microstrip antenna, double coupling mode is adopted to broaden the bandwidth,specifically, on the one hand, its feed use a L-type probe; on the other hand, a circular patch is coupled on the under square patch, they are resonant at high and low frequency point. This manner solves the problem of narrow bandwidth property in the existing microstrip antenna. The physical array antenna is made and tested, the results show that it’s height of 12 mm, VSWR<1.5 and other properties should comply with the design requirements.The two array antenna can be used in wireless communication systems in this paper. The further study based on this article should be expanded from the aspect of low side-lobe character of the array, other mode of helical antenna, and the structure and feeding method of microstrip antenna,etc.