Multiple-arm Slot Circular Antenna

With the application and development of Compass II Navigation Satellite System, more and more attention is paid to the circular polarized antenna, especially those having advantages of wide frequency band and low profile. In this dissertation, planar multiple-arm spiral slot antennas are studied with emphasis on the effect of characteristic parameters.The main works accomplished are as follows:1. The electrical performance of the single-arm Archimedean spiral slot antenna is studied as well as the feeding structure of this single-slot antenna, which shows good impedance matching. Then the double-orthogonal-arm Archimedean spiral slot antenna is proposed to improve circular polarization in this dissertation. Detailed analysis is made of antenna parameters and the features of the double-arm spiral slot antenna. It can be seen from the results that the circular polarization can be achieved with a 3-d B axial ratio bandwidth of 18 MHz and a maximum gain of 5.69 d B.2. A four-arm spiral slot antenna is designed to improve the axis symmetrical characteristic of the radiation pattern. Microstrip slot coupling mode is used for feeding the radiation slots, and shorted cylinder is introduced between the end of the microstrip feed line and the spiral slot planar. Electrical parameters, especially those of the feed line are studied in detail to clarify their influence on the impedance matching and circular polarization features. The results show that the antenna working at the center frequency of 1.268 GHz has a 10-d B return loss bandwidth of 105 MHz, broad 3-d B AR bandwidth of 25 MHz and high gain of 6.39 d B. What is more important is that only little variation in amplitude of pattern can be seen as the change of Azimuth angles, thus a desirable radiation pattern can be obtained.3. Based on the above research, an improved type of four-arm spiral slot antenna is presented. The antenna consists of different value of spiral growth rate and gap width with an opened microstrip feedline. It is seen that the impedance bandwidth of the antenna can reach 74 MHz, the AR bandwidth is 19 MHz and the peak gain is designed to be 6.33 d B.