Research Of High Performance Dielectric Ceramic And Its Application In Small GPS Antenna

Portable mobile communications devices tend to requires not onlyminiaturization，but also temperature stabilization and reliable performance. It iseffective to gain desirable performance and realize the miniaturization by improvingdielectric constant, quality factor Q value and temperature coefficient of resonantfrequency, which are the keys that can make sure the dielectric ceramics resistinterference wave efficient and adapt the environment well. As it is applied more andmore widely in modern communication field, developing microwave dielectricceramics of high performance is imminent.Usually, the higher the dielectric constant the more serious the dielectric loss is,which are contradicted with our goal of high dielectric constant and low dielectricloss. Besides, often its temperature coefficient of resonant frequency cannot reachusing requirements. So it is very difficult to meet the need of all the three. As so far,some frontier work is being down surround this problem, which is concentrated onthree aspects. One is to develop new material system of higher dielectric constant（>100or even>150）, the dielectric ceramics whoes dielectric constant is more than100are scarely reported. Moreover, its production repeatability is rather bad. So itcan hardly been commercialized. The other is to improve the quality factor Q to ahigher value （>3000）. The third is to make sure the temperature coefficient ofresonant frequency close to0（＜±30ppm/℃）.In this paper, high dielectric constant materials with plus and minus temperaturecoefficient are compounded to prepare dielectric ceramics of perovskite. By this way,we could adjust the temperature coefficient properly under the condition ofunchanging its high dielectric constant. Besides, we could improve the quality factorQ under the condition of low dielectric loss.This paper prepared high performance dielectric ceramics of CaTiO_3-(Li_1/2Sm_1/2)TiO₃by traditional solid phase method which is relatively mature with a small amountof Ca²⁺replaced by Nd³⁺, then sintering in air atmosphere.We also study the influence of process conditions on the performance. By addingseveral oxides and additives, the sintering temperature could be cut down. Finally, wedetermined the best technical parameters, under the condition of which, we gain thedielectric ceramics with εr≥120，Qf＞4200GHz，-15ppm/℃＜τf＜15ppm/℃, which can be applied in small GPS antenna. Besides, this dielectric ceramics have goodproduction repeatability. It has met the national requirement of high dielectricconstant microwave dielectric ceramic.As so far, the market has put forward higher request to the design andpreparation process of small GPS antenna. Most of them are imported.Miniaturization will lead to reduce of antenna gain and axial ratio, and finally worsenthe performance of antenna. Nowadays, the size of the widely used antenna is12×12×4mm. In the same ceramic body size of the reflection of the situation, itsantenna gain is-2dB and axial ratio is about5, which can be easily influent byenvironment.By determining the GPS antenna size, feed position, silver surface sizeparameters, this paper designed and prepared a kind of small GPS antenna with highperformance microwave dielectric ceramic we developed used in it. Besides, wedeveloped the method to control GPS antenna performance parameter. When theceramic body size is same and the size of the reflection is equal to the ceramic body,gain index can reach0db, and axis ratio can reach less3, the antenna performance areimproved and can work steadily and reliably in different environmental temperature.It realized the miniaturization of antenna on the conditions of guaranteeing thesensitivity and reliability of the antenna, which surpass the imported ones. Besides, ithas good production repeatability which suggested that it has the good foundation ofindustrialization.