Design And Research Of Microwave Miniaturized Filters And Diplexers

With the rapid development of 5G technology,multi-mode and multisystem signals coexist.In order to ensure the stable operation of the communication system,filters and diplexers with the function of isolating electromagnetic interference are widely concerned.At the same time,to meet the development needs of smart terminals under the 5G background,it is an important research direction to use integrated circuit technology to achieve both miniaturization and high performance of radio frequency(RF)front-end chips.In this thesis,two miniaturized dual-band bandpass filters based on low-temperature cofired ceramic technology(LTCC)operating at Sub6GHz and one miniaturized two-dimensional diplexer based on printed circuit board(PCB)technology operating at Wifi frequency band are studied for RF devices with the value of application in the 5G era.The details are as follows:1.A LTCC dual-band bandpass filter based on lumped elements is proposed.On the basic of the traditional bandpass filter,a dual-band bandpass filter with independent controllable transmission zeros is constructed through resonator transformation.This design also has the ability to expand to a three-pass filter structure.The even-/odd-mode circuit method is used to analyze the dual-band bandpass filter and determine the transmission zeros and poles.A dual-band filter chip operating at Sub-6GHz with a 3-dB fractional bandwidth of 25.45%/14.20%can be realized by taping out,and the size is 11.4 mm×6 mm,the insertion loss is only 1.38 dB/1.53 dB,and the return loss is 28 dB/23 dB.2.A miniaturized low insertion loss planar diplexer is proposed.In the ideal circuit,based on the Chebyshev bandpass filter prototype,a new K inverter is used to add the transmission zero and improve the roll-off.The structure diagram is realized by inter-digital capacitors and microstrip section inductors.The coupling effect is used to add the transmission zeros near the opposite channel and at the low frequency stop band without increasing the circuit size,and the isolation and stop band suppression are optimized.The two bandpass filters are connected by T-junction,and the final size is only 14.6 mm×10.48 mm.Based on the low-cost FR4 substrate,the insertion loss is only 1.67 dB and 1.58 dB,and the isolation between the two channels is better than 25.8 dB.3.A distributed dual-band bandpass filter chip with controllable bandwidth based on LTCC is proposed.A dual-band filter structure is constructed by using the T-type coupling lines and two short transmission lines.In order to verify the realization of controllable bandwidth,two dualband filters with different fractional bandwidths are designed,which operate at Sub-6GHz and Wifi frequency bands respectively.The correctness of the theory is verified by the even-/odd-mode half-circuit analysis method.The plane size after taping out is only 6.91 mm×7.2 mm,and 6.06 mm×5.76 mm,with excellent filtering performance and out-ofband suppression effect.