Research of 3 poles MCF commercialization

Mobile communication equipment including cellular phones are becoming smaller and lighter together with better performance. Monolithic crystal filters (MCF) have been designed as 2-poles MCFs in such a way that two pairs of electrodes are mounted on a crystal wafer. It is necessary to design a 4-poles tandem-connected MCFs which require the vertical connection of 2-poles MCFs even if the 4-poles attenuation is not required, for the purpose of improving the IF-stage frequency selectivity. In this case, these requirements adversely influence the design of MCF in terms of compactness and light weight as a turning circuit is required between filters in addition to the necessity to use 2-poles MCF. For this problem solving purpose, as trial design, 3-poles MCF was made and feasibility was studied if it could realize 1.5 times better attenuation compared with 2-poles MCF at same terminating impedance. As a result, it was confirmed that frequency adjustment of 3-poles MCF is possible by using Network Analyzer