Fully Inkjet Printed 85GHz Band Pass Filter on Flexible Substrate

In this paper, a fully inkjet printed mm-wave band pass filter on a flexible substrate is presented. Firstly, a side-coupled ring resonator is designed to extract substrate's dielectric properties at mm-wave frequency band. Then, a parallel coupled microstrip transmission line filter is designed at 88 GHz frequency band with 10 GHz bandwidth. The filter has been fabricated by inkjet printing without making any vias. Very small feature sizes of ~ 20μm have been reliably printed through new super inkjet printing technology. In addition, a Co-planar waveguide (CPW) transmission line and a CPW-to-microstrip transition have also been fabricated for comparison purpose. The filter's center frequency is 85.75 GHz with 20 GHz bandwidth, with potential applications fixed and mobile satellite communications. The insertion loss is ~5.8 dB, and overall return loss is below -10 dB. The rejection is lower than -20 dB.