Compact and high selectivity tri-band BPF using nested DDGSRs

A compact and high selectivity tri-band bandpass filter (BPF) is proposed. The filter has a dual-plane structure, which consists of three nested dual-mode defected ground structure resonators (DDGSRs) on the bottom layer and a pair of fork-shaped microstrip feedlines on the top layer. Using the intrinsic characteristics of the nested DDGSRs, three passbands as well as five transmission zeros near the passband edges can be generated simultaneously. An experimental filter with three passbands centred at 1.59 GHz (GPS application), 1.82 GHz (DCS application) and 2.44 GHz (WLAN application) has been designed and fabricated. The validity of this design approach is verified by good agreement between the simulated and measured results.

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