| With the development of wireless communication system,mobile satellite communication plays a more and more important role in our life.Portable mobile communication equipment has become a research hotspot.The equipment's antenna is required to have good performance in radiation,and its size should be as small as possible.The microstrip antenna and spiral antenna have good circular polarization performance,and they have been widely used in mobile satellite communication.In this paper,two mobile satellite communication antennas are designed for different terminals,and the miniaturization and portable design of the antennas are studied.The main research contents are as follows:1.Design of a S band portable circularly polarized microstrip antenna array.The methods of dual-feed and multilayer dielectric coupling are used for improving the impedance and axis ratio bandwidth of the antenna element,and the array is formed by the sequential-rotated feeding technique.Then we design a network of phase shift and power division.The feed network is composed of three 3-d B hybrid couplers and a delay line with length of λ/4.In order to adapt the array to the terminal,the folding design is used for miniaturizing the antenna array,and the flexible coaxial line is used to transmit signal at the folding point,so that the size of the array is reduced by half compared with the ordinary array when carried.The measured impedance bandwidth of the array in S band is more than 10.5%;the maximum gain can reach to 10 d Bi;and the top of the antenna's axial ratio is less than 3 d B.So the antenna array has good circular polarization performance.2.Design of a portable multi-frequency circularly polarized antenna for satellite communication.The combined antenna is designed with two kinds of spiral antennas,which can work in both UHF band and S band.In general,the UHF band antennas are of large size and difficult to carry,so a retractable quadrifilar spiral antenna working in UHF band is designed,which is improved on the basis of quadrifilar spiral antenna.And the radius of spiral arms of the antenna varies sinusoidal with height.In order to increase the bandwidth of the spiral antenna,a set of short coupling arms are added next to each spiral arm,so that the antenna can work in dual-frequency,and a miniaturized network of phase shift and power division is designed for it.The antenna in S band is designed with a quadrifilar spiral antenna printed on a cylindrical flexible substrate.Finally,The measured results show that the VSWR of the combined antenna is less than 2 both in UHF band(344-351.3MHz,389-396.3MHz)and S band(1.98GHz-2.01 GHz,2.17GHz-2.2GHz),and the gain is more than 2 d Bi during the elevation angle from 55° to 90°.So the combined antenna has great radiation performance in UHF and S bands. |
