Compact Dual-Band Bandpass Filter Using Asymmetrical Dual Stub-Loaded Open-Loops

A compact dual-band bandpass filter is proposed using asymmetrical dual stepped-impedance stub-loaded open-loop resonators, where additional transmission zeros are introduced so as to improve its upper rejection. Its mode characteristics and generation of its transmission zeros are analyzed theoretically. In such a filter, double resonators have different configurations, with their individual transmission zeros generated at different frequencies. It is demonstrated that the realized filter has good performance in frequency selectivity and spurious suppression. Also, good agreement is obtained between its simulated and measured S-parameters. Its –20 dB upper stopband is improved up to 2.57 times of the first central frequency, which is much better than its previous dual-band counterparts with small frequency ratios.

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