Study And Design On Novel Planar Differential Bandpass Filter

With the rapid development of modern wireless communication system,RF front-end devices play a more and more important role in the communication system,and the filter as an important part of RF front-end circuit,its performance directly affects the performance of the whole communication system.Compared with the traditional two-port circuit,the differential circuit has a stronger suppression effect on all kinds of environmental noise,so the differential filter has a wide application prospect.This thesis designs three novel differential bandpass filters,the main contents are as follows:Firstly,a single-frequency microstrip differential bandpass filter was designed based on the microstrip-slotline conversion structure.It consisted of a Folded stub load resonator（FSLR）structure and a pair of folded parallel coupling lines to realize the filtering characteristics.In particular,the loading of the folded parallel coupling lines make the filter generates an extra transmission zero,which improves the selectivity of differential mode passband.At the same time,the improved microstrip-slotline structure is applied to the feed structure of microstrip differential bandpass filter,and good common-mode suppression performance is achieved.Second,a dual-frequency differential band-pass filter was designed based on the Substrate Integrated Waveguide（SIW）structure.Based on the traditional rectangular SIW resonator and circular SIW resonator,a new structure combining two resonators is adopted.Two differential mode passbands are obtained by using TE₂₀₁ mode and TE₄₀₁mode of cavity.Two coupling windows are opened on the common rear wall of cavity1 and cavity 2 to realize the coupling between resonators.By adjusting the position and size of the coupling window,the center frequencies and bandwidths of the two bands can be determined.At the same time,the slotline structure is etched on the metal layer,the common-mode suppression performance is enhanced without affecting the differential mode transmission characteristics.Third,a double-layer differential bandpass filter was designed based on Circular SIW Resonator（CSIWR）.Two different modes of CSIWR laminated structure are used to realize the two differential mode passbands of the filter.First,two elliptic coupling vias are etched in the intermediate metal layer to realize the coupling between the two circular resonator,and to a certain extent,the common mode signal can be prevented from coupling to the next layer of resonant cavity.Then four metal perturbation vias are introduced to adjust the frequency ratio of the two passbands.Finally,the slotlines are etched on the surface of the upper and lower metal layers to further improve the common mode suppression.The thesis has 61 figures,7 tables and 98 references.