Terminal Antenna Design For Satellite Mobile Communications

The satellite mobile communication system (SMCS) has the advantage of wide coverage area, flexible networking, insensitive to topography, uninfluenced by the natural disasters, therefore well suited to remote area communication, special industry application, frontier and costal defense, overseas communication and the emergency communication in the natural disasters. Firstly, this dissertation explains the dimension design of the substrate integrated coaxial line (SICL), then develop the dual-band SICL branch-line coupler design and its compact version design. Ultimately, a dual-band antenna for the SMCS, using the SICL branch-line coupler as the feeding network is presented. The dissertation is organized as follows:Firstly, two dimension design methods for the SICL are proposed based on the theory of transmission lines. The first method is based on the field distribution and the second one uses the equivalent capacity of the transmission line. Then, the relations between the cut-off frequency and the dimensions of the SICL are derived. And the relations between the characteristic impedance and the dimensions of the SICL are also obtained. Using these two methods, the dimensions are computed. The SICL can be equivalent to the rectangular coaxial line with same characteristic impedance, which has a simpler structure. Simulation results validate the proposed methods.Next, dual-band SICL couplers with the conventional and compact structures have been designed, fabricated and measured at 1.60 GHz and 2.50 GHz as the operating frequencies. Both the EM simulation and measurement results of these two couplers have been provided. The proposed SICL coupler with the compact structure has comparable performance and a 66% size reduction rate compared to the SICL coupler with the conventional structure.Finally, a dual-band dual circularly polarized (CP) antenna fed by a dual-band 3-dB substrate integrated coaxial line coupler is designed, fabricated and measured. The proposed antenna is excited by two planar L-probes which are connected to two output ports of the coupler. This dual-band dual-CP antenna effectively covers L-band of 1.62 GHz and S-band of 2.50 GHz, respectively. Simulation and measurement results show that, considering reflection coefficient, gain, and axial-ratio together, the relative bandwidth is about 10% at lower band and about 4% at upper band. The maximum measured antenna gains are 8.5 dBi and 8.2 dBi, respectively.