A new impedance-transforming dual-band balun with filtering response and favorable output isolations

A new planar dual-band balun with filtering response and output isolations is proposed in this letter. The balun is constructed on a three-layer PCB, whose out-of-phase operation is realized by antisymmetric output configuration. By introducing dual-band resonators and admittance inverters, the circuit is able to operate with designated filtering response, and the source/load impedances could be different. Additionally, the output isolation is reserved by employing two isolation resistors. The experimental results prove that this new balun is a good candidate for multi-standard and multi-functional communications.