by Seong-Jun Kangand Hee-Yong Hwang, Kangwon National University Chuncheon, Korea
Most modern microwave communication systems require balanced components as well as unbalanced structures. In some wireless applications, such as dipole antennas, balanced LNAs, mixers, power amplifiers and so on, a balun frequently connects a bandpass filter with balanced components.1,2 Recently, simple balun-BPFs and their design equations have been proposed and found useful to reduce the cost and size of the functional blocks in some microwave systems.1,3 However, a conventional Balun-BPF shows unequal skirt responses between the two balanced outputs because one output has two notches near the passband, but the other does not have any, which also limits the skirt steepness of the Balun-BPF characteristics.
In order to eliminate the restrictions of the conventional Balun-BPF, two substantially identical ring resonators are combined. The arrangement of the combining points of the two ring resonators is essential to obtain symmetrical output responses. An interdigital-type inverter structure and the cross-coupling effect between two ring resonators are also investigated.
Analysis of the Dual Ring Balun-BPF
Figure 1 Schematic of the proposed dual ring Balun-BPF.
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