International Journal of Smart Grid and Clean Energy Analysis and Application of MEMS Microshield Line in Millimeter Filters Yue He, Jingfu Bao*, Yijia Du, Junwen Jiang School of Electronic Engineering, University of Electronic Science and Technology of China, Chengdu 611731, China Abstract This paper introduces the conformal mapping method for analyzing the quais-TEM characteristic of MEMS microshield line in detail. The conformal mapping method is an accurately method based on the Schwartz-Christoffel transformation which could invert the complex structure of the microshield line to the conventional plate capacitance. In this paper, the characteristic impedance Z 0 and the effect permittivity ε eff of the microshield line in wide dimension range are obtained. Making use of the simulation result, three filters are designed in millimeter frequency. Furthermore, the S-parameter of the filter indicates the filter designed by the line has good performance, low insertion loss and good out-band suppression. Keywords: Microshield line, millimeter wave, low dispersion 1. Introduction With the development of the communication system recently, the device in the system is required with the feature of low dissipation, small dimension and high performance in millimeter wave band, or higher frequency. But, the conventional coplanar transmission line, such as the microstrip line and the coplanar waveguide, exhibits bad performance in the millimeter wave band, especially in terahertz band. So, the performance of the device designed by the conventional transmission line is limited. In 1991 [1], a new transmission line, the microshield line, was introduced to make up the disadvantage of the convention line in high frequency band. The microshield line has superiority of low dissipation and dispersion in wide frequency range. Hence, the devices designed by the line have a good electrical performance. For investigating the characteristic parameter, in this paper, a conformal mapping method is introduced based on the Schwartz-Christoffel transformation [2]-[4]. Recently, some filters were designed by the coplanar waveguide [5],[6]. Because the conventional coplanar waveguide is similar to the microshield line in structure, so, in this paper, three filters is designed using the similar way to design filters by the former. Making use of the analysis result about the characteristic impedance Z 0 and the effective permittivity ε eff , three different filters are presented designed by the line. From the simulation result, the three filters have low insertion loss less than 1dB and good out-band suppression. The structure of the microshield line is shown in Fig. 1. The line consists of the upper wafer, the low wafer and the conductor line supported by a thin membrane (1.4 um Si 3 N 4 ). A cavity exists in the interior of the upper wafer with the metalized wall. Because the line is surrounded by the air, the wave propagation on the line could be treated as a pure TEM mode. It is the reason that the line would have good electromagnetism property in wide frequency range. * Manuscript received July 16, 2012; revised August 25, 2012. Corresponding author. Tel.: +86-028-61830365; E-mail address: baojingfu@uestc.edu.cn.