Application Note

Improving the Second-harmonic Passband Rejection of Microstrip Side-coupled Filters

Because of their low cost and easy manufacturability, side-coupled filters constructed from printed-circuit board (PCB)-based microstrip are widely used throughout the industry. One of the main drawbacks of the side-coupled filter is its limited rejection of the second harmonic. This application note demonstrates a solution that mitigates this problem through the introduction of notch-filter elements that improve the overall rejection of side-coupled filters at the second harmonic without significantly affecting the filter passband behavior.