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. >