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|Microwave Filters for RF/Microwave Circuits|
|Keywords: Microwave Filter, Microwave Circuits, Multilayer Ceramics|
|Passive RF filters, such as lumped, cavity, coaxial ceramic, microstrip/stripline and multilayer ceramic, SAW and BAW filters have been used in telecommunication, telemetry and other electronic applications. Most lumped, cavity and coaxial ceramic filters can be designed into SMT package format however; they are usually much larger than the SAW, BAW and multilayer ceramic filters. Cavity filters are the largest in size, but having very low loss today they still find many applications in wireless base stations. Coaxial ceramic filters are much smaller than cavity. Since the loss can be still low, it has been used in many areas from high power low loss to small size low cost applications. Lumped is mainly used to build lowpass or highpass filters although bandpass is also available. For CPE or hand held devices, multilayer ceramic, SAW and BAW are the only choice due to the cost and size constraints. Multiple layer ceramic filters are usually wide band filters due to the low Q of individual elements. SAW and BAW filters are electromechanical devices. Microstrip and stripline filters are mostly designed on the system board and used in higher frequency applications. As higher dielectric constant ceramic material becomes available, microstrip and stripline can extend applications toward lower frequency easily today. This paper emphasizes mainly on coaxial ceramic filter and microstrip and stripline filters. Coaxial ceramic filters are versatile since each resonator can be changed individually and coupling between resonators can be adjusted independently. Resonator numbers are adjustable. The cost and size are very reasonable. All these make it a good technology for prototype and medium quantity build. Ceramic multilayer, microstrip and stripline filters can be integrated into ceramic packaging more easily since the processes are compatible. Microstrip and stripline filters have wide band width and allow very wide stopband rejection to be achieved in small enclosures without the appearance of reentrant spurious passbands.|
|Edward Liang, President / CEO
MCV Technologies, Inc.
San Diego, CA