New Method for Transformation of Microstrip Lowpass Filter to Compact Bandpass Filter Using Defected Ground Structure(DGS) Coupled Resonators

In this letter, bandpass filter development with the assistance of the multi-layer transformation method, on the basis of the known Chebyschev-lowpass filter, is presented Boutejdar (2005). A new compact microstrip bandpass filter using three coupled arrowhead-slots in bottom-layer and a discontinuous 50Omega-microstrip transmission line in top-layer is proposed Boutejdar (2005). Both microstrip lines are coupled by means of a J-immitance inverter. If the width of the gap is changed, the center frequency would shift to the left or to right within a certain frequency range, and we can easily realize a tunable BPF. Three-pole-Chebyschev bandpass filter is fabricated, and tested at 7.25GHz