Research And Design Of Miniature High Performance Microstrip Bandpass Filter Based On LTCC Technology

In recent years, with the rapid development of mobile communication, national defense electronic systems and satellite communication, high performance, miniaturization and low cost have become important development directions for RF circuits. As the key device of the transmit-receive system, the performance of the filter will have vital impact on the whole system. Therefore, the research and design of filter with miniaturization and high performance is very urgent. In the ordinary course of events, the traditional filter can not meet all the requirements at the same time. However, the development of LTCC (Low Temperature Co-fired Ceramic) technology makes it possible to design a filter which has the performance of all the above.Miniaturization is the focus of the research of integrated circuits, electronic devices and other industries. LTCC technology has become the mainstream technology because it shows outstanding advantages of low impedance metallization, high frequency performance, cost, design diversity, integrated packaging, flexibility, wire line width, line spacing and other aspects of the field. Using LTCC technology, we can process microwave device with small size, high precision, good compactness and little loss. Because of the advantages of LTCC technology in three-dimensional integration, it is widely used in the microwave frequency to manufacture various microwave passive components, so that the high integration of passive components can be realized.In this paper, the microstrip bandpass filter is studied. Because the traditional microstrip line contact the air, the microstrip filter has a large insertion loss. Therefore, in this paper, we use new microstrip line with symmetric structure to improve the traditional microstrip filter, so the insertion loss can be reduced.In this paper, a total of two kinds of bandpass filters are designed, one is distributed microstrip bandpass filter, whose sizes are less than 4mm×3.5mm×0.5mm, and the other is an open-loop microstrip bandpass filter, the size of which is 3.5mm×4mm×0.45mm.Because of the advantages of low cost, small size and high yield, double layer structure is adopted in the design of distributed microstrip bandpass filter. We design two-order, four-order, and five-order filters. With the increase of filter order, the insertion loss of the filter in the pass band also has a certain degree of increase, but the steepness and the rejection of the stop band have increased, too. In order to further improve the performance of the side band and the suppression of the stop band, the four-order filter and five-order filter are improved with a Z-shaped microstrip line added to increase the cross coupling between non-adjacent resonant units, so the transmission zero is introduced near the pass band. At present, these two filters have been completed in processing and testing. At the same time, the open loop microstrip bandpass filter is also studied and designed. The approximation function of the open-loop microstrip bandpass filter is an elliptic function, which has higher resistance, better steepness, and more simple structure.In this paper, all the filters are fully meet the design requirements, with advantages of small size, excellent performance and low cost.