A new type duplexer with strip line filter

As one of the important technologies for mobile communications equipment, (especially portable telephones), filter technology is the key which provides high performance, compactness and lighter weight. The short-circuit of the λ/4-resonator made of high dielectric constant ceramics have been used in the case where sharp attenuation characteristics are required. SAW filters have been used where power conservation is not required. LC filters are examined from the point of compactness, lighter weight and lower cost. This paper proposes the configuration of a multi-substrate coil (MSC) in order to realize the characteristics of air-core coil in the LC filter by a multi-substrate with a low dielectric constant. Subsequently this paper reports the prototype filter for antenna couplers using this coil and an air-core coil in portable telephones in which high performance characteristics are required. The practicality of the MSC is also proved