Wideband Bandpass Filter Based on Flag Shaped Central Resonator

This work presents a novel wideband bandpass filter based on flag shaped central resonator with super-wide upper out band skirt rejection and a high selectivity factor. Bottom layer aperture with two stages based on three edge-coupled lines with centrally loaded flag resonator and lower stepped circular resonator contributes to the performance enhancement of the developed filter. The suggested bandpass filter has a fractional bandwidth of 103.5 % with a centre frequency of 5.8 GHz. The filter construction is optimized using the simulation software IE3D. The filter is made from a low-cost FR4 substrate with a thickness of 0.8 mm and a dielectric constant of 4.4. The centrally loaded flag resonator generates two transmission zeros, giving the filter structure an abrupt roll-off. The exceptionally wide upper stopband performance with greater than 30 dB suppression level is extended up to 22.3 GHz.