Design of Balanced Bandpass Filter Using Composite Right/Left-Handed Resonator With Attractive Common-Mode Rejection

In this paper, a balanced bandpass filter (BPF) with a wide CM suppression is designed by using the modified composite right/left-handed (CRLH) resonator. The differential-mode (DM) circuit and common-mode (CM) circuit of the proposed resonator are investigated by employing the even- and odd-mode method. In order to better analyze the resonant characteristics of the proposed CRLH resonator, an equivalent circuit model is established. Through proper design, a good CM suppression in a wide range of 1-10 GHz is finally achieved without loading additional circuits. The center frequency of the balanced BPF is 2.47 GHz and the FBW is 4.5%. Besides, by loading a quarter-wavelength open stub resonators on the feed microstrip line, additional transmission zeros are generated on the right side of the DM passband and such that the selectivity of the passband and the attenuation in stopband are improved. Finally, the effectiveness of the design method is verified by simulation.