Miniature Ltcc Dual-band Filter

With the rapid development of the wireless communication technology, the dual-band communication system operating at two different bands simultaneously is more and more important. As the key component of the dual-band communication system, the dual-band bandpass filter, whose size and performance have a significant impact to the whole dual-band communication system, is widely used in WLAN (Wireless Local Area Network) and dual-band portable cellphone.RF(Radio Frequency) passive components account for a large space in the system because of the inherent characteristics. Planar integrated technology is used to reduce the size, but still can not meet the stringent requirements. LTCC (Low Temperature Co-fired Ceramic) technology using three-dimensional multi-layer integration technique, makes it possible the realization of RF passive components with small size, high performance and low cost. This research is mainly about the miniaturized LTCC dual-band bandpass filter.There are already many researches about dual-band bandpass filter, however, most of them are based on planar integrated technology, which makes the relatively large size a problem for miniaturization. The research of the miniaturized dual-band bandpass filter with LTCC technology is more and more important, but the difficulty are the complexity of microwave passive device integration and the realization of highly density circuit, which are big challenges of this study.Considering the two passbands of the dual-band bandpass filter have influence with each other, matching network consisting of two inductors and two capacitors is introduced to realize impedance matching. A novel dual-band bandpass filter structure burying two stripline-type bandpass filters and the simple matching network in a single LTCC module is discussed. Thus two stripline-type dual-band bandpass filters are designed. The 2.4GHz/5.2GHz dual-band bandpass filter for WLAN, whose size is only 2.5mmx5mmx2.2mm, has the first passband of 2.35GHz-2.55GHz and the second passband of 5GHz-5.4GHz. Another 715MHz/1680MHz dual-band narrow bandpass filter has two passbands of about 4% bandwidth, and its size is 3.2mmx7mmx2.8mm.As the extending part of this research,a LC-type dual-band narrow bandpass filter operating at 4GHz/7GHz and a mixed-type dual-band bandpass filter combining with two different structure operating at 1.3GHz/2.4GHz are designed.To meet the stringent requirements, which include high stopband suppression,low insertion loss and good VSWR(Voltage Standing-Wave Ratio) in passband, high isolation between two passbands and high integration, small size, good performance, low cost and so on, transmission zeros used to realize high stopband suppression, high isolation between two passbands are introduced through cross coupling,besides matching network is used to realize the impedance matching of the two single-band bandpass filters. The dual-band bandpass filter consisting of two single-band bandpass filters in shunt and matching network is redesigned through inside structure adjustment and volume compression to realize the further miniaturization, thus two stripline-type dual-band bandpass filters are designed. In addition, a LC-type dual-band narrow bandpass filter and a mixed-type dual-band bandpass filter are discussed and designed. Comparing with each other, the advantage and disadvantage in size and performance of these different dual-band bandpass filters are discussed. This study not only has significant reference value for the research about miniaturized LTCC dual-band bandpass filter,but also can be referred for the integration of other LTCC RF passive components.