Reduced size microstrip fractal filter with suppressed second harmonic

This paper presents the design of a reduced size microstrip fractal filter. It has an added capability of suppressing the undesired second harmonic, located at twice the fundamental frequency. The basic configuration is the conventional parallel-coupled filter (CPC). It suffers from undesired spurious responses located at the second harmonic, which causes asymmetry in the upper skirt band. The undesired second harmonic can be harmful to components in a communication system. A CPC filter is first designed. Then, Koch fractal shape is applied, forming the KF filter. Finally, a reduced size fractal shaped, RKF, filter is designed by realigning the fractal sections. All three filters have been simulated and measured. It can be concluded that the employed fractal shape can improve harmonic suppression by a factor of 2. RKF is comparable to KF, but exhibits size reduction of more than half.