The Research And Design Of Reconfigurable Ultra-Wideband Planar Filter With Small-size

There is an increasing demand for electromagnetic spectrum in society.Wireless communications appliances with multi-functions and faster throughputs are created,which boost the development of dynamic reconfigurable and multi-function systems to utilize existing spectrum resources.Wireless devices in the future are expected to utilize multi-bands and other devices to communicate and fine tune services for customers.Each band may require a separate RF transceiver.This kind of modern multi-band and multi-mode communications systems need compact modules with high performances and highly integrated.Since the Federal Communications Commission(FCC)released the unlicensed frequency band 3.1-10.6 GHz for ultra-wideband(UWB)commercial communications,commercial UWB technology increases dramaticly all over the world.The aim of the article is developing reconfigurable UWB planar microwave filters.Some key problems in developing reconfigurable filters are discussed.These problems are usually emerged in the development and realisation of microwave filters recently.The author analyzes theoretically the realisation of functions of the filter.Two different types of elements to realize reconfigurable frequency are analyzed in this report.These kinds of elements are discrete(such as PIN diodes,optical switch)and continous(varactor diode)types.Equivalent circuits are considered and directly coupled filter structures are adopted.Several topologies with multi-function are developed for futural communication systems.This work consists of three following parts:In the first part,a square ring shape closed loop resonator along with a open-stub in symmetrical plane.In order to realize reconfigurable frequency in the same spectrum.A new method is proposed:the conventional PIN diodes are substituded with silicon wafer activated with near-infrared light.And the new one is compared with the conventional.In addition,in-band interference rejection could be realized from the external coupled T shape resonator structure.Utilizing the inner structure space of resonator could decrease the size of resonator apparently.In order to improve the frequency slectivity of filter,a convenient approach is adopted in the second part.A pair of transmission zeros are created between passband edges and one is created in stopband to reject harmonic.Based on the research in notched-band theory,the method of utilizing square ring shape structure to create single or mutiple notched-bands is proposed.This structure will not influence the performance of filter verified by experiment.This section involves theoretical details of filter designing procedure,simulation,and measurement results.The results of simulation and mesurement are in good agreement,verifying the good pratical performance.In the third part,a new type very compact planar dual-mode resonator has been proposed,with sharp rejections characteristic.The filter has a relative wide tuning range,low insertion loss,and good frequency selectivity.Finally,dual wideband and frequency bandwidth controllable indepently are realized by modifying dual-mode structure.After simulation and measurement,the filter performance is verified.