Research And Design On Electrical Tunable Filter

The modern wireless communication industry develops rapidly and spectrum resources are increasingly scarce.In order to improve the utilization of spectrum resources,Multi-pass band,dynamic frequency allocation and frequency hopping and other technologies are widely used,This trend makes the receiver more and more demanding of the filter,The electrically tunable filter can respond to the system requirements quickly and support multi channel communication.Therefore,more and more attention has been paid to the study of electrically tunable filters.The main task contains:1.The resonant characteristics of a 1/4 wavelength step impedance resonator(SIR)are investigated.The traditional SIR resonator is transformed,and a 5-bit frequency reconfigurable filter is designed and fabricated.The filter resonances at 2GHz,2.4GHz,2.6GHz,2.8GHz,3GHz,and a multi-bit frequency reconfigurable scheme is proposed based on the structure.2.The theory of mixed electric and magnetic coupling is introduced,and the key technology of the electrically tunable filter with constant absolute bandwidth is studied.An electrically tunable filter with the center frequency can be adjusted continuously from 2.5GHz to 3GHz is designed and manufactured,the absolute bandwidth keeps 150 MHz constant.And the method of extracting the external quality factor of the filter is introduced,a tunable filter with 100 MHz constant absolute bandwidth is designed,center frequency can be adjusted from 2.2GHz to 3GHz.3.The method of introducing the transmission zero point of the filter is introduced,a novel high-band rejection lowpass to bandpass switchable tunable filter is designed and fabricated,by introducing the transmission zero point by means of input-output loading open-circuit and mixed coupling.The design and introduction of zero point are discussed,and the reason of extra transmission zero point of the filter is analyzed.