Research And Design Of Miniaturized Functional Filter Based On LTCC Technology

With the rapid advancement of 5G commercialization work,human beings are about to move from “mobile internet” to “internet of everything”,and the demand and requirements for functional filters in the communications industry are also rising.Low Temperature Co-fired Ceramics(LTCC)technology can easily achieve small,high-performance microwave components with its unique multi-layer 3D integration capability.At present,functional filters are widely used,among which balun filters are commonly used in wireless communication fields such as Bluetooth and wireless LAN,common mode filters are often used in the field of squelch,and absorptive filters are commonly used in high-gain power amplifier circuits and sensitive receiving circuits.However,how to realize the miniaturized high-performance functional filter has always been a research hotspot in the microwave field.This paper focuses on the LTCC miniaturized functional filter.The main research results are as follows:(1)The resonant characteristics,coupling characteristics,phase-shifting characteristics of the comb-line structure are analyzed in detail.On this basis,a comb-line balun filter is proposed.For the insufficiency of insertion loss and working bandwidth,the coupling technology through connecting lines is introduced to improve without affecting the size of the device.The performance of the new balun filter is greatly improved,and the size is only 4.5mm*3.2mm*1.5mm.After processing and testing,the effectiveness of the coupling technique achieved by the connecting lines is verified.(2)Combined with the working principle and software testing method of common mode filter,a stacked spiral common mode filter is designed.On this basis,the common mode rejection of the new common mode filter is further improved by reducing the Q of the device and loading the grounded capacitance at the two output ports without increasing the device size,and the insertion loss of the differential mode is slightly increased.The final size is only 2mm*1.25mm*1.2mm.(3)The coupled cancellation principle of the absorptive bandpass filter is analyzed in detail.According to the theory,the designed fourth-order comb-line bandpass filter,eighth-order comb-line bandpass filter and 3dB orthogonal directional coupler are combined to realize two absorptive bandpass filters,each with wide absorptive bandwidth,high stopband suppression and low insertion loss.The final sizes are 8.4mm*5mm*2.5mm and 12.8mm*5mm*2.5mm respectively.The former was processed and tested,and the results proved the effectiveness of the design.