Novel ultra wideband printed balun design using the FEM and FDTD methods

Three different baluns have been designed using FDTD and verified by HFSS. It has demonstrated that all baluns have good return loss at the UBLP from 2 to 18 GHz when their BLP are connected with matched loads. Although balun-1 has the longest UBM to BM converting section, it has the lowest insertion loss when the wave transforms from UBM to BM. The length of balun-2 is much shorter than the length of balun-1, but it has higher insertion loss than balun-1 from 4 to 17.5 GHz. This is because some high order modes have to be generated to adapt to the unexpected changes introduced by the slots in the ground plane. The advantages of balun-3 are: (i) it is shorter than balun-1; and (ii) the CDS is used at the BLP. Further investigations will be carried out experimentally to verify these balun designs.