Attenuation pole type dielectric filter for duplexer

The mobile terminal duplexer consists primarily of transmitting/receiving filters and a branching circuit. The filter consists primarily of a semicoaxial resonator, which is made of material of a high dielectric constant for compact components. A dielectric filter with attenuation pole and a novel branching circuit which have been developed by OKI for compactness and higher performance are introduced. The attenuation pole is implemented by connecting an additional circuit based on a capacitive-coupled bandpass filter. Three circuits are discussed: a circuit comprised of three-resonators with an attenuation pole on each of the lower and higher frequency sides of the passband, exhibiting symmetrical characteristics; a circuit with an attenuation pole only on the higher frequency side of the passband; and a circuit with an attenuation pole only on the lower frequency side of the passband. The filter features compactness (25% smaller, as compared with older models), and small insertion loss.<>