A broadband and miniaturized balun on system-in-package (SiP) technology

A broadband and miniaturized balun is proposed on low temperature co-fired ceramic (LTCC) substrate using the artificial coupled line with strong even-mode suppression. The artificial coupled line represents as a metamaterial transmission line for the even mode excitation, whereas it behaves like a TEM transmission line with approximately constant characteristic impedance for the odd mode excitation. Based on the artificial coupled line, a wide stopband for common mode is presented to design a balun on system in package (SiP). This balun is realized using LTCC fabrication technology, simulated by a full wave tool, and measured in a three-port VNA system. It exhibits a good amplitude imbalance of 0.3 dB and a phase imbalance of 179° ± 3° with the return loss greater than 10 dB from 3.3 to 7.1 GHz with 73% of FBW. Its electrical size is only 0.063 × 0.44 λ_g² and its physical size is 1.6 × 11.2 mm². It is a good candidate for a passive balun integrated to SiP systems due to its compact size with broadband operation.