Distributed-Element Absorptive Bandpass Filter with A Broadband Impedance Matching

In this paper, we present a new method for designing absorptive bandpass filters using coupled lines. The new design method and filter structure allow an absorptive bandpass filter to have good impedance matching performance over a wider frequency range in comparison with distributed-element absorptive filters reported in the literature. Closed form design equations are provided so that a filter can be designed in a way to produce a target frequency response. For verifying the presented design approach, a second-order absorptive bandpass filter centered at 2 GHz having 10% fractional bandwidth has been designed, fabricated, and measured. The measurement shows that the return losses (S
11
and S
22
) are overall larger than 10 dB from DC to 3
$f_{0}$
.