Multilayer bandstop filter for ultra wideband systems

A multilayer broadside-coupled microstrip-slot-microstrip structure is used to design a bandstop filter with a wide passband for ultra wideband (UWB) applications. The design procedure for the proposed filter is based on the conformal mapping technique and the even- and odd-mode analysis. The theoretical analysis indicates that value of the coupling factor between the top and bottom layers of the structure can be used to control the width of the stopband, whereas centre of that band can be controlled by the length of the coupled structure. To limit the passband of the proposed bandstop filter to 3.1-10.6-GHz, which is the specified bandwidth for UWB systems, a broadside-coupled bandpass filter is integrated with the proposed device. The simulated and measured results show that the proposed device achieve -0.5-dB insertion loss across most of the passband and -20-dB insertion loss at the stopband. The device also shows a flat group delay across the passband with -0.15-ns peak-to-peak variation. Hence, it is a suitable choice for the UWB systems that require a distortionless operation.