Design for Harmonic Waves Suppression Based on 3 ㏈ Branch Line Coupler

Design for Harmonic Waves Suppression Based on 3 ㏈ Branch Line Coupler

This paper presents a structure of the 3 ㏈ Branch Line Coupler that can suppress the nth harmonic wave output. The 3 ㏈ Branch Line Coupler consists of two pairs of λ/4n open stubs, which are located at the λ/4 series arms symmetrically. We established an optimal design method employing Powell's Least Square Method to design the circuit structure. Experimental results show that this 3 ㏈ Branch Line Coupler suppresses the 2nd and 3rd order harmonic waves frequency components to less than -25 ㏈, while maintaining the characteristics of a conventional 3 ㏈ Branch Line Coupler; featuring an equal power split, a simultaneous impedance matching at all ports and a good reflection and isolation. These results agree well with the simulation results.