Lst-4 Wideband Crystal Filters Developed

The crystal filter is a kind of device with selectivity to frequency signals. It plays a crucial role in communication system. The performance of crystal filter directly affects that of communication system. In recent years, more and more wide-bandwidth crystal filters are required with the growing communication signals bandwidths. But the bandwidth of quartz crystal filter is limited by the crystal resonator used. To design wide-bandwidth crystal filters can satisfy the requirements of modern communication system and widen the operation fields of crystal filters. So the design of wide-bandwidth crystal filter is significant to the development of crystal filter.The dissertation describes the background of this subject and the application; expatiates the development of crystal filter in history and nowadays; introduces the theory of crystal filter; mainly interprets the design principle of crystal filter; introduces the design and manufacture of wide-bandwidth crystal filter in details.In this dissertation, theory analysis was preceded with wide-bandwidth crystal filter and it was simulated. This thesis work can be summarized as follows:1. By using the theory of network, we analyzed the relationship between the filter bandwidth and the zero-pole spacing of crystal resonator. The comparison of zero-pole spacing in theory and practice are given.2. By expressing formula of resonant frequency adding an inductor in series, we induced the relationship between frequency deviation and the value of adding inductor. That is helpful to compute crystal frequency in filter design.3. By using the ADS simulation software, the wide-bandwidth crystal filter was simulated. The S-parameter simulation results were presented. The products designed with simulation are in agreement with the required technique item.I took the responsibility of designing and manufacturing the crystal filter in most aspects of this project. The project lasted more than two years before the products had been measured and the project passed expertise appraisal. It achieved the research demand and gained good performance expected before.