The zero at DC is imposed by the end-coupled line whilst the higher-frequency transmission zero is generated by the above DGS pattern. Thus, additional stubs and DGS elements are required toobtain the needed bandpass response; for example the ones with two finite zeros near the proximity of the passband edges. In this paper, a novel open-loop dumbbell-shaped DGS unit isproposed. It offers a quasi-elliptic bandpass characteristic bounded by dual finite controllable transmission-zeros. It is found that these two zeros can be controlled by the DGS dimensions, so that BPFs with different center frequencies and bandwidths can be easily designed. To examine the usefulness of the proposed DGS unit, two quasi-elliptic BPFs centered at 1.5GHz using one and two units are designed and compared with the traditional bandpass type DGS BPF as well as ideal quasi-elliptic bandpass model, respectively.
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