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Properties of a quarter-wavelength coplanar waveguide resonator such as resonant frequency, external quality factor(〓_e)are characterized by a theoretical approach and verified by the experiment. The unloaded quality factor(〓_e)of the resonator is also examined experimentally. After new types of combline bandpass filter(BPF)made of these resonators are realized, their transmission and reflection characteristics are examined theoretically and experimentally. A new combline BPF having attenuation poles are also realized. A simple method to produce two-port equivalent circuit of these BPF is presented in this paper. The transmission characteristics including such as the control of attenuation poles of these filters are explained by the created equivalent circuit with the concept of even and odd modes. A new method of describing attenuation poles is estabilished.