Design Of Broadband Bandpass Filters Using LTCC Technology

This paper mainly presents the methodology of the design of fully embedded broadband filters realized by LTCC technology based on introducing LTCC manufacturing process and the methods of designing high-frequency circuits in LTCC technology. For the need of the design of high frequency LTCC circuits, the structures of lumped inductors and capacitors are established in the software HFSS. Their equivalent-circuit models are obtained and the values of the various components in the equivalent-circuit models are extracted directly by the simulated parameters. The magnitude and the phase of S11 and S21 generated from the equivalent circuit models are compared with the three-dimensional inductors and capacitors, it can be seen that the equivalent circuit models for three-dimensional inductors and capacitors embedded in the multilayer LTCC substrate can catch higher frequency than the SRF, the effective bandwidth is wide. The method of optimizing the performance of three-dimensional lumped inductors and capacitors is proposed through the simulation of various structures of three-dimensional inductors and capacitors and analysis of the effective values and Q values in HFSS. The performance parameters of various structural parameters of lumped capacitors and inductors in LTCC are extracted and the effects of the structural parameters on performance parameters are found.According to the theory of the tapped combline filter, a five-order Chebyshev bandpass filter is designed with a center frequency of 15.5GHz, with a bandwidth of 1GHz, with the insertion losses in the passsband less than 1.6dB and the return losses more than 30dB. The volume occupied by the filter is 4.3mm×2.8mm×0.95mm. According to the principles to design a bandpass filter, the ideal circuit model of the filter is obtained by using Ansoft Designer. Based on equivalent-circuit models, three-dimensional physical circuits of the filter are established by rational placing the lumped capacitors and inductors in the multilayer LTCC substrate, and a five-order lumped-element Chebyshev bandpass filters was designed after optimizing the structural parameters of the lumped capacitors and inductors, the volume occupied by the filter is 7mm×4mm×1.14mm. The center frequency of the bandpass filter is 2GHz, the bandwidth of it is 1GHz, the insertion losses in the passsband less than 1.3dB and the return losses more than 15dB. The performance of the filter meets all the requirements.