Design Of Miniaturized Balun And Filter Based On LTCC Technology

Based on the study of the Balun's principle and the characteristic of even-odd mode impedance of coupling transmission line, two Marchand Baluns with the center frequencies of 1.35GHz and 1.70GHz are designed by LTCC technology respectively in this paper. Through modeling and simulating by HFSS, the width of coupling line that influencing on the function of Marchand Balun is studied, and two methods of changing the even-odd mode impedances of the coupling region are proposed that improved the Marchand Balun's function. Each size of these two Marchand Baluns is 3.2mm×1.6mm×1.3mm and 3.2mm×1.6mm×1.15mm respectively.Regulations and methods of introducing the transmission zeros into lumped filter are studied, and the attenuation characteristics of different types of lowpass filters are analyzed by Designer. Based on the design specification of the filter, an elliptic seven-order miniaturized lowpass filter with the cut-off frequency of 1.35GHz is designed by HFSS. Through optimizing the physical structure of the proposed filter, the performance of the proposed filter is improved by avoiding the parasitic and coupling effects between the internal elements. The simulated results show that the cut-off frequency is 1.35GHz, and the cut-off rate from the passband to stopband is steep, and the suppression from 1.61GHz to 3.10GHz is more than 40dB, and the remote suppression from 3.10GHz to 6GHz is more than 30dB. The characteristic of the proposed filter can meet the requirements of high performance application.