Research On Miniaturized Planar Passive Microwave Filters In Wireless Communication Systems

In recent decades,with the rapid developments in wireless communication technology and consumer electronic products,there is an ever-increasing need for the miniaturization of the systems.As the key frequency-selectivite components in the communication system,the volume and frequency response of microwace filters have a significant impact on the system's performance.With the feature of flexible design,compact-size and low cost,the microstrip filters have become one research hotspot in the wireless communication technology.The main work of this dissertation is as follows:First of all,the cross coupling matrix synthesis theory and frequency dependent coupling matrix synthesis theory are illustrated in this dissertation.The theory of genetic algorithm and gradient optimization algorithm on the optimization of the frequency dependent coupling matrix is discussed in this papar.The validity of the algorithms are verified by serveral examples.The extraction methods of the electromagnetic coupling coefficient and the external quality factor are illustrated.Second,a series of trisection frequency dependent filters based on the frequency dependent coupling matrix theory and embedded design idea are discussed and studied.Based on the uniform impedance resonators,an embedded type trisection frequency dependent filter is designed and studied in this dissertation.In this filter,the frequency dependent coupling between the first and the third resonator is achieved by separate electronic and magnetic couipling paths.The second resonator is embedded in aera between the first and the third resonator and coupling with them.This new trisection topology can generate two transmission zeros in the stopband of a filter.These transmission zeros effectively improve the selevtivity of a filter.The embedded structure compacts the filter which occupies an area of 6.1 mm×8.8 mm.Subsequently,a ring-like stepped impedance resonator(RSIR)is proposed in this paper,and the characteristics of the resonator are studied.The area inside the ring can be taken by other microstrip structures,which keeps the volum of filter unincreased along with the improvement of the performance.Based on the RSIR,the embedded design idea and the trisection frequency dependent topology,a trisection frequency dependent filter with embedded half-wavelength dual-spiral resonator,a trisection frequency dependent filter with sourceload coupling and a trisection frequency dependent filter with embedded half-wavelength ring-like stepped impedance resonator are designed and studied in this paper.There are 3 or 4 transmission zeros in the stopband of frequency response of the three filters which improve the frequency selectivity of the filters.The embedded structure makes the filters' compact volume.The area of the circuits is 10 mm×5 mm,10 mm×5 mm and 13 mm×8 mm,respectively.Then,a series of dual-band bandpass filters are designed and studied in this paper.First,an open stub loaded uniform impedance resonator is proposed in this paper.Based on the resonator,a dual-path frequency dependent coupling dual-band filter is designed.There is one transmission zero located near each side of the two passband of the filter,which improves the frequency selectivity.The filter is compact with a circuit area of 8.5 mm×8.5 mm.Secondly,an open stub dissymmetrically loaded RSIR(SL-RSIR)which based on the RSIR is presented in this paper.The stub and loaded point of the SL-RSIR can be arbitrarily chosen which make the design of the resonator very flexible.Meanwhile,due to the the dissymmetry,the traditional method to study a stub loaded ring-like resonator can not be used to analyze the SL-RSIR.A circuit network analysis method based on the two-port network theory is introduced to study the SL-RSIR.A frequency dependent coupling filter and a full specification coupling filter using the SL-RSIR are designed and studied.The frequency selectivity of the two filters are superior due to the transmission zeros located at edge of passbands.Meanwhile,the loaded open stubs of the resonators are folded into the ring parts of the filters,which makes the filter very compact.The area occupied by the fiters are 4 mm×8 mm and 6 mm×15 mm,respectively.At the end of this section,the RSIRs mentioned in the last part are used in designing an embedded type dual-band filter with the feature of high frequency selectivity and compact circuit size.The final part of this dissertation involves the application of the frequency dependent coupling filters in the power dividers(PD).Combining filters and PD can make a filtering PD.The filtering PDs have the feature of frequency selecting and power dividing at the same time which can miniaturize the size of the system.Two filtering Wilkinson PDs which have improved frequency selectivity,low insertion loss,high isolation and compact size are designed in this paper.