A fully inkjet-printed 3D transformer balun for conformal and rollable microwave applications

An original design and prototype for the first-time reported low-cost inkjet printed 1:4 GHz planar, multi-layer transformer is presented. The proposed transformer is a balun and consists of a three-parallel turns center-tapped primary coil and a two turns, including overpasses, secondary coil for conformal and rollable antenna applications. The hosting substrate is Liquid Crystalline Polymer (LCP) by Rogers Corporation, the conductive layers are realized through the nano-particle silver inkjet printing technique and the dielectric layers, used to separate the overpasses of the turns, are made by means of SU-8 inkjet printing. Based on the fabrication technology, we achieved a design with a good maximum available gain (MAG) of about -1.765 dB (given the lossy conductive ink) and high self-resonant frequencies of the coils. The MAG indicates that 67% of the input power is received at the output, given appropriate matching. The transformer has an inductance of 6.1 nH and 14.2 nH for the primary and the secondary respectively at 1.4 GHz. The simulated k-factor is equal to 0.49.