A miniaturized ceramic bandpass filter for cordless phone systems

Miniaturized band-pass filter, which size is 3.0 mm/spl times/2.0 mm/spl times/1.5 mm, was developed by two different dielectric ceramics with low and high permittivities. The filter was constructed by putting strip line made by high permittivity ceramics (/spl epsi//sub r/=75) between micro strip line made by low permittivity ceramics (/spl epsi//sub r/=15). As its filter characteristics, two attenuation poles were observed at the lower frequency and higher frequency than the pass band. The reason for two attenuation poles´ appearances was discussed using the theoretical equivalent circuit.<>