Many bandpass filters operated in different frequency bands and wireless communication systems are required in order to provide various services such as LTE, WCDMA, Wi-Fi, etc. Smart phones provide several communication services using one platform. In considering front-end reconstructions, the case of a frequency tunable filter is used in the platform is better than the case of the number of bandpass filters which are used in the platform in terms of cost and size. Therefore broadband communication systems expecially need a frequency tunable filter.
There are many types of frequency tunable filters such as YIG filters, active filters, etc. YIG filters have a weak point in size and price. Active filters have a disadvantage of power handing capability and need a temperature compensation circuit. This dissertation presents a design and implementation of filter banks for the feasibility test of a cavity tunable filter.
The operating frequency band of 800 MHz ~ 1600 MHz, the frequency band most likely used in mobile communications, is divided into 6 sub-frequency bands for making the filter bank. First the circuit of filter banks is simulated and then the resonator of the circuit of filter banks is converted into cavity resonators. The designed cavity resonators with tuning screws are optimized in physical dimensions with CST Microwave Studio. Measurement results show that the implemented filter bank has the maximum 0.372dB of insertion loss and 20 ~ 40 MHz of bandwidth. And attenuation characteristics measure the range of 19.974 dB ~ 35.285 dB at the frequency of band edge from ±60 MHz apart. Experimental results demonstrate that if the depth of a tuning screw of resonators in the cavity filter cloud be controlled by electrical or mechanical method, cavity tunable filters can be implemented with maintain and the required specifications.