Wideband bandstop filter using hybrid microstrip/CPW‐DGS with via‐hole connection

A novel wideband bandstop filter (BSF) with a minimum attenuation better than 28.5 dB and three transmission zeros within the stopband is proposed. The designed filter is composed of a top microstrip transmission line and a bottom coplanar waveguide open‐circuited resonator loaded by a periodical L‐shaped defected ground structure resonant unit cell. The top and bottom dual‐metal‐plane conductors are connected by the periodically metallic via‐hole within the designed substrate. With the appropriate height of substrate and separation between the adjacent metallic via‐holes, an excellent parallel‐plate‐metal synthesised transmission line with an improved coupling between the top and bottom resonators can be achieved by this via‐hole‐loaded technology. Finally, a microstrip BSF centred at 5.44 GHz with a measured 20 dB rejection bandwidth of more than 35.5% are designed, fabricated, and measured for this topology of validation.