Design And Fabrication Of SIW Filter Based On LTCC Technology

Filter,as an important part in the front end of modern communication system,has a continuously expanding demand market because of the upcoming fifth generation communication system.The function of microwave and millimeter-wave circuit system is becoming more complex.The index is getting higher,while the volume is turning into smaller.Therefore,miniaturization,high performance and integration become the development trend of modern filter.Substrate Integrated Waveguide(SIW)structure,inherits both the advantages of the traditional metal Waveguide,such as high Q value,low loss and the merit of microstrip circuit such as small size,easy package,low cost at the same time.Low Temperature co-fired Ceramics(LTCC)technology has the characteristics of high density package,excellent high frequency performance,fine wiring structure and three-dimensional integration.The combination of LTCC technology and SIW structure provides an effective foundation for filter's miniaturization,high performance,and integration.Based on the SIW structure and LTCC technology,a series of multilayer miniaturization and high performance SIW filters are studied.(1)A kind of third-order multilayer compact Chebyshev bandpass filter was designed adopting the high dielectric SICCAS-K70D material(?_r=66,tan?=0.002)based LTCC for S band fourth generation communication.The frequency of the S band filter in the design is 2.6 GHz.The bandwidth under the 20 dB return loss is 125MHz.The relative bandwidth is 4.82%.The insertion loss is 1.82 dB.And the dimension is 25.9mm×15mm×2mm.The filter was fabricated using LTCC multilayer processes.The measured performance of filter and the simulated performance of the designed filter are in good agreement except the frequency shift.This work showed the feasibility of the structure of LTCC multilayer miniaturized SIW filter and the advantage of high dielectric LTCC material in miniaturization.(2)The Ka band third-order bandpass filter is proposed by introducing the coplanar waveguide vertical transition to solve the signal connection between different layers and adopting SICCAS-K5F3 LTCC material(?r=6.2,tan?=0.002)for Ka band fifth generation millimeter wave communication application.The simulated filter has a center frequency of 27.95 GHz and an insertion loss of about 1.73 dB,and a 3 dB bandwidth of about 11%.The fabricated filter shows a center frequency of27.73 GHz and an insertion loss of about 1.74 dB.And the 3 dB bandwidth is about10%.The consistency of the simulated and measured results is good,which verifies the good frequency characteristics of LTCC materials under millimeter wave and the structure of multilayer miniaturized SIW filter.(3)Aiming to the high performance LTCC device with low insertion loss,different types of SIW cavity were studied.Two different bandwidth rectangular SIW filter and a circular SIW filter were designed under millimeter-wave frequency.Increasing the thickness of single-layer dielectric substrate,a rectangular SIW filter with center frequency of 25.7 GHz,and 20 dB relative bandwidth of 7.9%,the insertion loss of 0.52 dB is achieved.The center frequency of the circular SIW filter is26.5 GHz,and the relative bandwidth of 20 dB is 4.9%,and the insertion loss is 0.77dB.The insertion loss of the SIW filter is reduced from nearly 2 dB to lower than 1dB.The results prove that improving the Q value of the SIW cavity can significantly reduce the insertion loss of the filter to achieve the practical application requirements.(4)The Q value of air-filled SIW cavity is analyzed and compared with the unfilled SIW cavity.The Q value increased nearly three times by using the air-filled SIW cavity.The air cavity is introduced into the planar SIW filter to makes a further improvement of the filter's performance.The insertion loss of the 26 GHz bandpass filter decreased from 1.49 dB to 0.69 dB,which further validate the high Q features and good potential in millimeter wave application of the air-filled SIW.