Design of a broad-bandpass filter using microstrip/CPW structures with PBG substrate

Compact broad-bandpass filters based on the composite microstrip/coplanar waveguide (CPW) with Photonic bandgap (PBG) are presented. The transition between the microstrip and CPW is based on the electromagnetic frequency characteristics and leads to surface coupling between microstrip and CPW. By controlling the CPW slots and microstrip conductor width, wide bandpass filters can be obtained. The PBG is used to force a band stop response at the higher end of the passband. Numerical results show that the return loss is less than -10 dB over the frequency range of 7.5-20.5 GHz which is suitable for the applications of the Ku band. The finite difference time domain method (FDTD) with perfect matched layer (PML) is used in the present analysis.