Design Of The Microwave Filters Based On LTCC Technology

With the development of wireless communication technology, microwave passivedevices are developing toward the direction of smaller, lighter, high-performance andlow-cost. Most of the traditional process technology cannot meet the demand of theminiaturization of devices, while the low-temperature co-fired ceramic (LTCC)technology makes small and high-performance microwave passive components possible,because of its stack process and the layout way of three-dimensional.Small size microwave filters based on the LTCC technology are studied in this paper.Firstly, it extracts the valid values, quality factors and self resonant frequencies of theburied inductors and capacitors. The influences of the geometric size, shape, dielectricconstant and other parameters to the valid values, quality factor and self resonantfrequency of the buried inductors and capacitors are researched. Based on the analysisof microwave filters’ basic theory, it introduces the design methods of low pass, bandpass and high pass filters. Finally, this paper designs three types of microwave filters,the step-impedance and lumped LC type low pass filters with the cut-off frequency of1.5GHz; step-impedance type bandpass filters with center frequency of1.9GHz andlumped LC type band pass fitlers with center frequency of1.2GHz, with the bandwidthof500MHz; the high pass filter with the cut-off frequency of900MHz and thebandwidth greater than2GHz. What’s more, this paper uses the HFSS software tosimulate and analyze the filters designed above. The simulation results show that theinsertion loss in the pass-band of the lumped LC low pass filters is less than1.3dB, andthe suppression in the range of1.8GHz to6GHz is greater than35dB. For the high passfilter, the pass-band VSWR is less than1.3, and the suppression is greater than20dB inthe range of500MHz to700MHz and greater than40dB in the range of DC to500MHz.In addition, all of the microwave filters meet the design requirements well, and thelumped LC type filters have a dimension of smaller than4.8mm×3.2mm×1.5mm. Sothese filters achieve the goal of the miniaturization to microwave passive devices.