Fabrication And Optimization Of L Band Tunable Filter

With the development of the information age, communication channel congestion is getting worse. In order to improve the communication quality, a single communication system capable of covering different communication channel is required to realize signal transmission in different frequency(frequency-hopping communication).Then the tunable filter as a core component of the frequency hopping communication equipments, has received widespread attentions from different researchers. Due to the characters of small size, fast response and easy to set up, the ferroelectric tunable filter is the most potential filter for high-performance frequency-hopping communication systems. Based on existing laboratory conditions and previous research, this paper mainly focus on the fabrication and optimization of the BST ferroelectric tunable filter.The main contents and results are as follows:1.By reducing the annealing temperature and cooling rate, we fund that it can effectively avoid cracking of the film due to the thermal expansion coefficient different between sapphire and BST material. According to the test results of the capacitors, the dielectric constant of the BST ferroelectric thin film on sapphire substrate is about 160,the dielectric adjustment rate is greater than 40%(bias is 40V) and the dielectric loss is less than 0.02.2.In the thickening process of the top electrode, the fine structure of the filter can easily cause a short circuit. To avoid this situation, we introduce a new method to thicken the top electrode. In the production process using this method can reduce a lithography process, not only simplifies the process steps and also reduces the production error. To some extent, use this method can improve the quality of the filter.3.A comb-line tunable filter with the resonant frequency of 1.14 GHz has been successfully fabricated on a sapphire substrate. The insertion loss of the filter is reduced about 8dB by thickening the top electrode. According to the measured results of the filter, we optimize the original structure of the filter, finally simulate the new structure.4.The circuit simulation software ADS and electromagnetic simulation software HFSS is used to design a lumped LC tunable band-pass filter with the center frequency of 890 MHz and bandwidth 180 MHz. When dielectric adjustment rate is set to 30%, thecenter frequency of the filter move to 1080 MHz, the center frequency adjustable rate is about 21.3%. DC signals can be loaded directly through the port during use a large capacitance as the bias circuit. By using this method, we can simply the process of dc signal bias. Finally all the designs are verified by the electromagnetic simulation.