Nanowire-Based 3-D Transmission-Line Transformer for Millimeter-Wave Applications

In this letter, 3-D transformers based on transmission lines (TLs) working at mm-wave frequencies are presented. They were realized in a low-cost technology based on metallic-filled nanoporous membranes. Several transformers were designed and measured with different numbers of turns, from 1 to 6 turns. They exhibit working frequencies from 14.5 up to 110 GHz. The 1-dB bandwidth (BW) of the realized transformers is better than 12 GHz, and the insertion loss (IL) is between 1.1 and 1.6 dB, thus demonstrating a high efficiency at mm-waves. Transformers could be further improved by better optimizing the TLs and their return current path, which is a key parameter to be considered, given the distributed nature of the proposed transformers.