Research On Balanced Filter Based On SIW Structure

In recent years, bandpass filters have played important role in rapid development with wireless communication systems, which have received more and more attention. The substrate integrated waveguide (SIW) structure has stimulated an interest in academia due to its inherent characteristics, just naming a few:low loss, high quality factor, high power-handling capability, low profile, easy fabrication, good integration, etc. In order to reduce the size of SIW structure, a new guide wave structure named ’half mode substrate integrated waveguide (HMSIW)’is proposed. Balanced bandpass filters (BPFs) have recently attracted special attention because of good signal to noise ratio characteristics in wireless communication systems. Balanced bandpass filters based on microstrip structure have been deeply and widely researched, whereas which can not work in millimeter waves. However, the SIW and HMSIW structures can be employed in millimeter waves effectively. In this dissertation, the author has proposed several balanced filters based on SIW and HMSIW structures, which have multiple functions and outstanding common-mode suppression for potentially commercial applications.After the basic theory of the SIW structure, design of SIW and microstrip line transition structure and introduced the transmission zeros are summarized, then the field distribution of cavity has been analyzed. The TE102- and TE202-modes can effectively transmit the differential-mode signal and reject the common-mode signal. The slotlines are etched on the top metal of cavity, which can improve the common-mode suppression in the resonance frequency of TE201-mode and the second differential-mode passband. In final, dual-band balanced bandpass filter based on SIW has been designed. The dual-band balanced bandpass filter with improved the common-mode suppression has also been presented. The measured and simulated results are in good agreement.In addition, high selectivity balanced bandpass filter and dual-band balanced bandpass filter based on HMSIW structure have been also proposed. The field distribution of TE102-mode of HMSIW structure is similar to the TE102-mode of SIW structure, which also effectively transmit the differential-mode signal and reject the common-mode signal. Firstly, the basic balanced filter based on HMSIW should be designed. Secondly, the slotlines and EBG structure should be added in basic HMSIW balanced bandpass filter to realized the high selectivity and dual-band response, respectively. Compared with SIW structure, the size of HMSIW structure will be greatly reduced. The experimental results are in good agreement with theoretical and simulated results.