Inkjet-printed interdigital coupled line filter on liquid crystal polymer substrate

This letter investigates inkjet-printed interdigital coupled line bandpass filters on liquid crystal polymer substrates. Silver nanoparticle colloidal solution was used as the printing ink. Various numbers of passes were used to print the samples to study the changes in conductivity and uniformity. Samples were then sintered in an oven to remove excess solvent and material impurities. The silver-film conductivity of the conductive ink was ${\sim}1\times 10^{7}~{\rm S}/{\rm m}. The interdigital coupled line bandpass filter was printed with an inkjet printing system. The study achieved a minimal insertion loss and maximal return loss of {-}{3.6} and {-}{\rm 24}~{\rm dB} at 25.7 GHz, respectively.