A method aiming to widen the upper stopband in a microwave bandpass filter based on two-conductor suspended-substrate stripline resonators is described in this letter. Applicability of the method is illustrated by simulating and fabricating fourth-order filter that has a very wide upper stopband: Δfstop/f0=7.92 measured at a level -50 dB, which is achieved because the widths of the inner resonators in the structure are 1.4 times greater than that of the outer ones.
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