Design Of LTCC Bandpass Filter Used In ISM Band For Wireless Communication System

High performance and miniaturization are the current trends in the wireless communication systems. Therefore, new technological approaches are required to address the integration of passives. One of the important means today for integrating passives, particularly for RF functional passive modules, is low-temperature cofired ceramics (LTCC).The bandpass filter is considered as one of the most important components in the RF front-end. It can select favored signals in the passband and immunize other signals in the stopband. This paper mainly about the design methods and process of LTCC filters. The main contents and innovations are as follows:1. Research of traditional filter design method. Based on the traditional filter design theory, by changing the resonators to obtain transmission zeros, and gives the design formulas. This paper also lists some typical types of lumped circuit of bandpass filter.2. Design of embedded LTCC components. The expressions of inductor and capacitor were analyzed and concluded. 3D structures and their each equivalent circuit models of inductor an capacitor had been simulated by AWR and HFSS respectively. Then introduce the stepped-impedance resonators (SIR), and proposed a new structure of SIR. This new SIR has a good realization of the resonator mentioned above.3. This paper proposes a third-order bandpass filter using low temperature co-fired ceramic (LTCC) technology. The filter employs two grounding inductors, connecting the two parallel LC resonators, to provide a transmission zero in the upper stopband. A feedback capacitor between input and output is also used to generate two transmission zeros. With the help of stepped-impedance resonators (SIR), the filter has a compact size of 2.5mm×2.0mm×0.9mm. The insertion loss is less than 1.3dB from 2.40GHz to 2.50GHz in passband.