The Analysis Of Sequential-Phase Fed Circularly Polarized Antenna

Antennas play an important role in the whole wireless communication systems. The circularly polarized antenna is widely employed in satellite communication and navigation systems owing to its numerous advantages. With the development of satellite systems, the low cost, easy processing, high performance circularly polarized antenna is an important research direction in the field of antennas. The dissertation focuses on the sequential feeding circularly polarized antenna and a slot helix antenna with a simple and efficient feeding network for satellite communications and global positioning system(GPS) applications is presented. The dissertation mainly includes the following aspects:First, the principles of N elements circular array are studied. The radiation field of any element is decomposed into a right-hand circular polarization component and a left-hand circular polarization component. The superposition of radiation field components results show that the circularly polarized radiation can be realized by setting every array element equal amplitude and 2p/N phase difference between adjacent elements. For higher frequency microstrip traveling wave fed array applications,the length of microstrip is set to gm ×l instead of gl because of the limited space, the number of elements N should be equal to the divisors of m-1 and not equal to the divisors of m+1. The circularly polarized radiation can be realized if this condition is met.Then, according to the above theory, a slot helix antenna is designed and analyzed. This antenna has a similar radiation pattern with traditional quadrifilar helix antenna but its feeding network is much simpler and four or more slot radiating elements can be equipped. The feeding network includes a circular transmission line which connect to ground plate by a loaded resistor, six slotted openings couple energy from transmission line. Good circularly polarized radiation is achieved by adjusting the fan-shaped slots to make sure every slot have equal amplitude and appropriate phase difference between adjacent slots. The experimental results show that the antenna works at GPS L1 band and has a relative bandwidth of 9.23%, 3-dB axial ratio bandwidth is about 3.2%, ranging from 1.553 to 1.604 GHz and the peak gain is about 4.77 dBic at the centre frequency.