Ａ Method for Improving Out-of-Band Characteristics of a Wideband Bandpass Filter in an LTCC Substrate

Recently, compact wireless modules using low temperature co-fired ceramic (LTCC) technology are widely used for the wireless systems such as mobile phones, Bluetooth, and wireless local-area networks(Lin et al.,2004; Wang et al.,2005). Fig.1 shows the general structure of the compact wireless modules using the LTCC technology. The modules consist of an LTCC substrate, integrated circuits, chip components, a shield, and passive components embedded in the LTCC substrate (e.g., the bandpass filter, coupler and balun). The embedded components in the LTCC substrate are fabricated by using the multilayer structures based on thin ceramic sheets and conductor patterns. It becomes possible to produce very compact modules compared to those with a general printed circuit board substrate, because a number of passive components can be embedded in the substrate. To adapt this technology for ultra wideband (UWB) wireless systems, a wideband bandpass filter in the LTCC substrate is one of the most important technology because it decreases the influences from other wireless systems. Various wideband bandpass filters have already been presented(Ishida & Araki, 2004; Saitou et al.,2005; Li et al., 2005; Zhu et al.,2005; Horii