Compact wideband-balanced bandpass filter with high-selectivity and wideband CM suppression

A wideband-balanced bandpass filter is presented using two half-wavelength transmission lines, two coupled lines and one-stepped impedance stub. Compared to the reported wideband-balanced bandpass filters, the proposed one shows the advantages of small total length, high-frequency selectivity and wideband common-mode (CM) suppression. The bandwidth of CM suppression and differential-mode transmission, and the positions of transmission zeros are controllable by the parameters. One prototype was designed, fabricated and measured with the total length of 2λ g (λ g is the guided wavelength at the centre frequency f 0), 3 dB fractional bandwidth of 61% and 15 dB CM suppression bandwidth of 3.67f 0.