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Narrow-band performance is obtained with inductive loads and with series or parallel resonance circuit loads. In Figure 2 is shown the dispersion curves in the case of an inductive load and with series and parallel resonance loads. Negative values of 0 d 3 ᑬ͕1/␣͖ can be realized with resonant loads. In the same curve we find backward wave region, also called "left-handed" region, when the group velocity is negative. It is possible to reach the desired optimum performance or tune the waveguide properties by changing the h/d ratio. The results show that we can have large qd values, thus making strong spatial variations in field along the array. Extremely slow waves and resonant modes exist. At a certain frequency, when the group velocity v g is zero but the phase velocity v p is nonzero, a standing wave in the array is observed, and therefore a resonator can be realized. Formulas (3.6) and (3.7) are extremely useful when one analyses resonance structures because the functions are well behaved and rapidly converging. This saves computer time and the formulas can also be expressed in a compact form. REFERENCES 1. V.S. Veselago, The electrodynamics of substances with simultaneously negative values of and .

BPF. A three-stage BPF is fabricated in order to further improve the skirt at the outband performances in both lower and upper stopbands. All design parameters are the same those of the onestage filter except w 3 ϭ 0.1 mm, w 4 ϭ 0.24 mm, and w 6 ϭ 0.23 mm. The total length except 50-⍀ feed line is 23.48 mm. Figure 5 shows the measured and predicted frequency responses of the three-stage BPF. The skirt performance at the outband is sharper than that of the one-stage. Its measured and predicted maximum insertion loss are both less than 2.4 dB and the measured group delay varies between 0.27 and 0.73 ns with a maximum variation of 0.46 ns over the UWB band. CONCLUSIONSIn this letter, a novel UWB BPF using a DUC-EBG unit cell with multiple-mode resonance is presented for size reduction. This proposed filter has been demonstrated by various experiments and analyzed using the equivalent circuit of the DUC-EBG cell. The distributed L-C component values of the DUC-EBG cell are found using curve-fitting with the measured S-parameters. Moreover, a three-stage filter is designed and fabricated to improve the skirt performance. This design is very useful for UWB applications as the compactness is needed. REFERENCES