Research On Broadband RF Filters In Next-generation High-speed Wireless Communication Systems

In recent years,the high-speed wireless communication systems,represented by the fifth generation(5G)mobile communication system,have attracted much attention.As one of the key devices of wireless communication system,the performance of the filter has a significant impact on the performance of the whole system.Hence it has become a hot research topic of the field of millimeter-wave.Substrate integrated waveguide(SIW)is widely used in filter design owing to its low insertion loss,high quality factor and easy integration with planar circuits.Therefore,this thesis investigates SIW filters in the three potential frequency bands of the 5G communication system and the terahertz band,respectively.The main work is as follows:Firstly,two small broadband planar filters are designed with a passband range of 9-15 GHz and 25-30 GHz for potential 5G communication system,respectively.In order to overcome the shortcomings of the conventional SIW filters,such as the large size in low frequency and the limited bandwidth,the parallel-coupled stripline is used as the main structure which is enclosed in the middle layer by SIW to reduce the radiation loss in this paper.The designed filters have a low insertion loss owing to the self-packaged structure.Experimental results show that the proposed filters have good performance.Secondly,a planar Q-band bandpass filter is designed by using SIW technology in this paper.The Q-band is also one of the candidate band of 5G communication system.The bandpass filter is presented by cascading a low-pass and a high-pass filter,the high-pass is designed by utilizing the high-pass behavior of the SIW and the low-pass filter is realized by using five millimeter-wave lump-element resonators.The proposed bandpass filter has a center frequency of 42.5GHz and a fractional bandwidth of 11.76%.The measured results show that the designed filters have the advantages of low-insertion loss,high selectivity and a flexible bandwidth.This work has been accepted by Wiley,Microwave and Optical Technology Letters and is being published.Finally,a G-band bandpass filter based on electromagnetic bandgap(EBG)structure is developed.A low-pass filter with a cutoff frequency of 190GHz is investigated by using the stop-band characteristic of the periodic EBG structure,and then a bandpass filter range from 180GHz to 190GHz is developed by cascading the designed low-pass filter with a high-pass filter with a cutoff frequency of 180GHz which is designed by the high-pass performance of SIW.At last,the designed filters are connected with the fine-line transition and fabricated by using low cost Printed Circuit Board(PCB)process to verify the design.This work has been submitted to IET Electronic Letters and is under review.