Highly selective wideband bandpass filter using combined microstrip/coplanar waveguide structure

A highly selective wideband bandpass filter using a combined coplanar waveguide (CPW) and microstrip structure is proposed. The CPW section is responsible for creating a 4–8 GHz bandwidth. The microstrip split ring resonators and shorted coupled lines are used to sharpen the transitions between the passband and the stopband at lower and upper edges. The CPW section is fed by a microstrip host line and consists of two symmetrical coupled stepped‐impedance resonators to limit the bandwidth of the desired filter. A lumped element circuit model is presented and comparisons with experimental and simulation results confirm great compatibility and performance. The measurement results confirm a return loss larger than 15.3 dB in the passband, an out‐of‐band rejection greater than 15 dB.