Design Of Electronically Tunable Filters Based On Microstrip Open Loop Resonators

Along with the rapid development of modern wireless communication systems, frequency spectrum has become more and more crowded. In order to improve the usage of frequency spectrum, the spectrum technologies such as multi-band, hopping frequency, spread spectrum and dynamic frequency allocation have been widely used, which has greatly promoted the development of fast electrically tunable or configurable filters. In military communication systems, to meet the requirement of anti-jamming, microwave electrically tunable filters are applied for fast frequency hopping.In this thesis, research on the design of electrically tunable filters is performed based on the microstrip open loop filter theory. The major work done can be categorized as follows:1. A summarization is done to the various tuning devices used for electrically tunable filters and different tuning technologies are compared.2. The design of electrically tunable dual-band filters is studied. Centrally loaded varactors are employed to obtain the tunable second pass-band with the first pass-band fixed.3. The design method of harmonic-suppressed tunable band-pass filters is presented. Varactors are attached at the two ends of open loop resonators, making the center frequency of the pass-band tunable. However, due to the change of even-mode response, it is quite difficult to suppress the harmonics. In this thesis, two methods are proposed to suppress harmonic response, which are centrally loaded resistor and capacitance, and portly loaded inductance and capacitance.Based on the proposed method, co-simulation is made by implementing tools like IE3D and ADS for fast and accurate design. Two filters mentioned above are fabricated and tested. Simulation and measured results are compared. Good agreement is obtained which validates the design method discussed in this paper.