Miniaturized Multi-layered Wide Band Microstrip BPF with Sharp Transition Band

The concept of broadside coupling in multi-layered substrate is used here to implement a wide band band pass filter (WB-BPF). Here in this design two substrate layers are considered to design the filter. A pair of transmission line is coupled to provide a wide band pass response with the aid of three defected structures at ground. One of the transmission lines is placed at the top plane of the upper layer and another transmission line is at bottom plane of the lower layer. The coupling between these two transmission lines at different plane is obtained through the modification at ground that is sandwiched between two substrate layers. The filter has compact size and exhibit passband which is fully controllable and having center frequency at 5.65 GHz. The fractional bandwidth (FBW) of the filter is 139.8%. The filter has -3 dB cut-off frequency at 9.6 GHz and a 22.5 dB rejection at 9.9 GHz. The upper transition band is only 0.3 GHz.