| With the rapid development of wireless communication and the increasing demands for information, nowdays, more and more wireless service equipments are needed for cars, especially for luxury cars. They have systems not only for standard AM-/FM-reception but for TV-reception, keyless entry, remote control functions, satellite navigation, mobile phone, and in future, digital radio as well. So a lot of radio systems come into being for these service equipments. Antenna as the front-end equipment of radio systems, it plays a vital role in the whole system, its performance directly affects the level of reception system.Micro-strip antenna has many profits. These are low volume, light weight, thin profile configuration which easy to be made conformal and easy to be integrated with microwave circuit. So it is widely used in various radio systems. In order to realize invisibility, the paper makes efforts to make the antennas into micro-strip structures to integrated conformal with car body.Firstly, this thesis looks back to the history of car antennas, briefly introduced the current research and the trend in the future. Then summarized the design methods of car antenna at present, explained the radiation mechanism of micro-strip antenna.Secondly, many common methods to achieve miniaturization were researched, such as adopting special materials, loading technology, winding current technology, fractal technology and some other special structures.Finally, this thesis designed three types of novel micro-strip antenna aimed at the application of car. One is a 2.4GHz super thin micro-strip antenna, the thickness is just 0.4mm and it can be applied to wireless toll system, vehicle management system and so on. The main structure of the antenna proposed is consisted of a cirque patch on the top of the substrate and a ring patch on the bottom. And in the bottom, also there is a micro-strip which is connected to the cirque patch. The feed point is on the side of the ring patch. The length of the gap between the cirque patch and the ring is about half wavelength. The whole structure is very simple and it can be easily installed on many positions of a car. Between 2.4GHz and 2.4835GHz, VSWR is belowl.3. The second one is a vehicle telephone antenna. The radiator of the antenna is an ellipse ring and the ground was adopted a trapezoidal structure which can reduce the sizes. Whole structure was printed on the both sides of a PCB board. A gradual changed micro-strip connected the feed point and the radiator to make the impedance matched. VSWR of all bands is below and the peak gain reaches to 4.06dBi. So it can apply for mobile telephone net. The third is a GPS antenna. Basic structure of that is a hexagon on one side of the PCB board and the ground on the opposite side. On the ground, two pairs of slots which are different length were dug out. The slots not only changed the path of current for achieving the goal of reducing sizes, but also realized circular polarization. After continuous optimization, the proper position for the feed point was found on the diagonal. So the antenna gets better performance. In the 1575.42±5MHz band, VSWR is belowl.3 and the gain is about 2dB. This antenna can installed on the top of a car or integrated with car sunroof. So it can get good invisibility. All the three antennas proposed above can satisfy the demand of the applications, so they have many application prospects. |
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