Photodefinable microcomposites for antenna applications

EPON™ SU-8 is a negative-tone photoresist which has been extensively used in UV and Xray lithography for fabrication of various mechanical and optical structures. In this work SU-8 is studied as a polymer binder for antenna applications. It is reinforced with different weight percents of alumina (AI₂O₃) micropowder. Up to 2 mm thick rectangular slabs are lithographically produced with optimized X-ray exposure dose and time. To measure the permittivity of the resulted materials, a new approach consisting of the multilayer microstrip theory and ring resonator technique is utilized. This method was found to be simple but satisfactorily precise and results in wideband dielectric constant measurement. The possibility of ultra-thick slab fabrication with flood exposure along with the measured permittivity of the photodefinable microcomposite materials reinforces the potential of direct fabrication of microwave and antenna devices using X-ray masks. As an example, dielectric resonator antenna (DRA) microcomposite structures are designed and fabricated with this method. The antennas are measured at millimeter-wave frequencies and show a wideband performance in a slot-coupled feeding structure.