Monolithic Compact Low-Frequency Bandpass Filter Based on Intertwined Helical Resonators

This paper reports on a new type of a compact 3D bandpass filter using intertwined helical resonators. The filter design is based on coupled-resonators theory and the manufacturing employs stereolithograpy apparatus (SLA) 3D printing to obtain a monolithic 3D screwless structure with low weight and low loss. To validate the results obtained through simulations, a prototype has been manufactured and measured, showing the following RF characteristics: frequency of operation of 1.08 GHz, fractional bandwidth of 15.5 %, minimum in-band insertion loss of 0.08 dB and Q
eff
equal to 1805.