Ultra-Miniaturized, High-Performance Filters on Alumina Ribbon Ceramic Substrates for 5G Small-Cell Applications

This article demonstrates ultra-compact, high-performance filters with footprint smaller than <tex-math notation="LaTeX">0.602λ ₀ × 0.125λ ₀ </tex-math> , operating in 39-GHz frequency band, on ultra-thin alumina ribbon ceramic (ARC) substrate, a newly developed material technology at Corning Inc. Bandpass filters (BPFs) with three topologies, i.e.,edge-coupled, hairpin, and interdigital, together with quasi-lumped elliptical low-pass filters (LPFs) are designed on 80- <tex-math notation="LaTeX">μ m </tex-math> -thick ARC substrates and fabricated using a semi-additive patterning (SAP) process. Characterized from 14 to 50 GHz using a vector network analyzer (VNA), filters on ARC exhibit excellent model-to-hardware correlation and outstanding performance with respect to passband insertion loss (IL), return loss, selectivity, and out-of-band rejection. Moreover, they depict a very flat group delay within the passband with a maximum variation up to 0.058 ns. Showing an IL less than 1.43- and 0.95-dB at the cut-off frequency and mid-band frequency, respectively, LPFs and BPFs demonstrate a size reduction of up to 93% and 86%, respectively, compared to their counterparts on other substrates, while outperforming them as well. These highly miniaturized, integrated filters with high <tex-math notation="LaTeX">Q </tex-math> -factor are best-suited for RF front-end modules (FEMs) and mobile handsets in 5G and millimeter-wave (mm-wave) frequency ranges, indicating the potential of ARC for such applications.