| In recent years, mobile communication develops rapidly. The technologies in satellites, multimedia and networks also come into use, with the appearance of many kinds of new services, such as GPS, mobile TV broadcasting, mobile internet connection, etc. Great changes appear from communication theory to software and hardware realization, from satellites to terrestrial networks, from base stations to mobile terminals. Mobile TV broadcasting is very popular for its largest target group. In 2006, China set CMMB as the industrial standard of mobile multimedia broadcasting, which also made the related researches more and more attractive.In this thesis, receiving plans of CMMB satellite signals for vehicle use and the design of corresponding antennas are studied. Receiving antennas with polarization diversity are used. Two kinds of dual-CP, wide beamwidth antennas are designed. The impact of some structures on antenna performance is analyzed. Besides, studies on the widely used base station array antennas are carried out. Two kinds of directional array antennas for TD-SCDMA base stations are designed, which simplify the structure and satisfy the requirements.Firstly, an overview of backgrounds and significances is given, together with the introduction of antenna types for satellite signals reception, and diversity techniques and latest developments. Normal types of base station antennas and basic theories of smart antennas are also briefly described.Then link budget is made for CMMB system to get the radiation pattern's coverage and gain requirement. Fading channel and basic propagation models are discussed to demonstrate the necessity of terrestrial compensation network and corresponding analysis. Ray tracing method is used to analyze multipath propagation. Expression of the dual-path signals and change of polarizations are given using GTD and reflection theories, based on which the easy change of CP waves'polarization direction and axial ratio (AR) are analyzed. Thus the plan, which uses a diversity antenna with dual-CP and wide beam features, is given, also proved by a correlation analysis, with comparisons and selection of the combination methods.Specific design of the antenna is studied. An aperture coupled dual-CP microstrip antenna with a parasitic patch and a large ground reflector is proposed, based on the diversity plan, antenna requirements and the vehicle condition. Fundamental mode and high mode antennas are designed respectively, with good matching and isolation features. The beamwidth with good gain and AR features are large enough to satisfy the requirements. The fundamental mode antenna gets a beamwidth of 148°, in which AR is less than 3dB, while the second-order mode antenna has a radiation pattern or AR pattern exactly pointing to the corresponding region. The effects of the parasitic patch and ground size are analyzed in details to demonstrate the improvement of antenna performance especially the AR feature.Besides, specific design of TD-SCDMA base station antenna is presented. An orthogonally placed rectangle patch dipole and a slotted ellipse patch dipole are proposed to realize a simplified structure, a lower profile, an improved current distribution and a higher gain. Two plans, combined with different feeding and calibration networks, are designed, fabricated and tested, realizing good matching, with gains higher than 15dB, an exact tilt down angle, a 3dB beamwidth larger than 7°in E-Plane and larger than 90°in H-Plane and a front-back ratio approaching 30dB. |
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