Modeling and characterization of copper tape microstrips on paper substrate and application to 24 GHz branch-line couplers

In this work, a new technique to fabricate microwave circuits in paper substrates is adopted. This technique relies on a copper adhesive tape that is shaped by a photo-lithographic process and then transferred to the hosting substrate by means of a sacrificial layer. Microstrip lines in paper substrates have been electromagnetically characterized accounting also for the adhesive layers. Then a simple CAD model is proposed and experimentally validated in the microwave frequency range. Measured results show an insertion loss of about 1.8 dB/cm at 30GHz. Finally, a branch-line coupler, working at 24 GHz has been designed using the previous characterization, fabricated and measured. The experiment shows a 4.1 dB insertion loss in good agreement with the simulations.