A Wideband Bandpass Filter With Ultra-Wide Reflectionless Range For 5G Applications

With the development of modern wireless communication system,the demands for wideband bandpass filters(BPFs)with broad stopband are increasing for high data rate and rejecting interference from other wireless systems.However,conventional BPFs reflect the signals of stopband back to the source,which cause the intermodulation interference and gain fluctuations in the mixer and high gain amplifier for practical wireless communication applications,especially the 5G wireless communication.In recent years,many reflectionless filters based on various methods and structures have been proposed by the academia.Nevertheless,the reported reflectionless filters implemented by lumped-element or microstrip-line suffer from the fundamental limitation of narrow bandwidth and poor stopband performance.Therefore,the design of wideband bandpass filter with broad stopband and ultra-wide reflectionless range still remains a great challenge.Moreover,such filter is attractive for the application of 5G wireless communication.In this dissertation,a wideband bandpass filter with broad stopband and ultra-wide reflectionless range is proposed for 5G applications.Firstly,the theoretical analysis of two channels with duplexer architecture combination is carried out.According to the conditions of reflectionless and bandpass,the S parameters of each channel can be calculated.Secondly,the microstrip T-junction and the defected ground structures(DGS)are utilized to realize the main channel with bandpass and broad stopband frequency response.Thirdly,the hybrid ring slot/microstrip loaded-stub are used to achieve the auxiliary channel with band-stop and wide passband frequency response.Finally,the spur-line is utilized for stopband performance enhancement.The measurement results illustrated that the passband range of the filter is 3.3-5.0GHz,covering the n77 and n79 frequency bands of the 5G New Radio,and the minimum insertion loss is 1d B.In addition,the stopband rejection level of 30 d B is extended to 27.4GHz,and the reflectionless range(return loss greater than 10 d B)is 10MHz-26 GHz.With such good performance,the proposed reflectionless filter is attractive for 5G applications.