Advanced Materials and Technologies High-temperature superconductors (HTS), ferroelectrics, micromachining or microelectromechanical systems (MEMS), hybrid or monolithic microwave integrated circuits (MMIC), active filters, photonic bandgap (PBG) materials/structures, and low-temperature cofired ceramics (LTCC) are among recent advanced materials and technologies that have stimulated the rapid development of new microstrip and other filters. This chapter summarizes some of these important materials and technologies, particularly regarding the applications to microstrip or stripline filters. . | Microstrip Filters for RF Microwave Applications. Jia-Sheng Hong M. J. Lancaster Copyright 2001 John Wiley Sons Inc. ISBNs 0-471-38877-7 Hardback 0-471-22161-9 Electronic CHAPTER 7 Advanced Materials and Technologies High-temperature superconductors HTS ferroelectrics micromachining or microelectromechanical systems MEMS hybrid or monolithic microwave integrated circuits MMIC active filters photonic bandgap PBG materials structures and low-temperature cofired ceramics LTCC are among recent advanced materials and technologies that have stimulated the rapid development of new microstrip and other filters. This chapter summarizes some of these important materials and technologies particularly regarding the applications to microstrip or stripline filters. SUPERCONDUCTING FILTERS High-temperature superconductivity is at the forefront of today s filter technology and is changing the way we design communication systems electronic systems medical instrumentation and military microwave systems 1-4 . Superconducting filters play an important role in many applications especially those for the next generation of mobile communication systems 12-17 . Most superconducting filters are simply microstrip structures using HTS thin films 18-44 . For the design of HTS microstrip filters it is essential to understand some important properties of superconductors and substrates for growing HTS films. These will be described in the following section. Superconducting Materials Superconductors are materials that exhibit a zero intrinsic resistance to direct current dc flow when cooled below a certain temperature. The temperature at which the intrinsic resistance undergoes an abrupt change is referred to as the critical tem- 191 192 ADVANCED MATERIALS AND TECHNOLOGIES perature or transition temperature denoted by Tc. For alternating current ac flow the resistance does not go to zero below Tc but increases with increasing frequency. However at typical RF microwave frequencies in the
