Design and fabrication of 40GHz hairpin filter using Printed Circuit Board

This paper presents the implementation of classical hairpin filter using Printed Circuit Board (PCB) for gigabit wireless application in the millimeter-wave band. The filter has been designed for 2GHz bandwidth at 41GHz center frequency. The filter samples were fabricated using 127μm thick Rogers RT/Duroid 5880 with Ground-Signal-Ground (GSG) pads to facilitate probe measurement. The first cycle of fabrication revealed that the Dielectric Constant (Dk) for designing hairpin filter using RT5880 is lower than the specified process Dk. The second trial exposed that hairpin filters are very sensitive to process tolerance. The filters for the subsequent fabrication manipulated design Dk of 2.1 and tighter process tolerance. The filters then show improved passband shape and return loss. However, the fabricated filters provide larger passband with slightly shifted center frequency than the simulated result due to inaccurate setting in the simulation tool. Nevertheless, the fabricated filters are still valid to be used for the intended application.