Realization of Integrated Miniature Ceramic Filters for 900 MHz Cellular Mobile Radio Applications

This paper discusses development work aimed at designing and manufacturing small integrated ceramic band-pass filters to be used in portable 900 MHz mobile radio telephone sets. Interdigital and comb-line types of filters investigated were made of Ba2Ti9020 (¿r=37) and Ba (Sm, Nd)2Ti5O14 (¿r=78) ceramics. Miniaturization of the filters was possible by using irregular structures such as grooves or cuts between the resonators and by optimizing the number of band pass and band stop resonator elements. The simulated and measured responses of the filters after trimming were in reasonable good agreement. During the design small size, simple structures and low manufacturing costs of the filters were emphasized.