A novel high-selectivity bandpass filter based on a defected ground structure and substrate integrated coaxial line is proposed. Three transmission zeros near the passband are achieved by introducing a divergent-shaped resonator and two spindle-shaped defected ground structures, resulting in a high selectivity. To verify the proposed structure, one prototype with a center frequency of 4.94 GHz is designed and fabricated. The measured results show that three transmission zeros respectively located at 3.92, 4.36, and 6.00 GHz are obtained. The 3-dB passband bandwidth is 14.2% from 4.59 to 5.29 GHz. The upper stopband rejection is better than 20 dB from 5.71 to 11.31 GHz.
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