Super compact and ultra-wideband bandpass filter using bridged-T coils

An ultra-wideband (UWB) bandpass filter (BPF) with super compact circuit size is proposed, which is realized using bridged-T coils. By replacing all the transmission line sections of a tri-mode resonator with bridged-T coils, the filter size can be largely reduced while the original frequency response remains almost intact. The proposed filter structure can then be conveniently realized with semiconductor IC process to achieve super compact circuit size. Specifically, an UWB BPF with a passband from 3.1 to 10.6 GHz is demonstrated using a commercial GaAs pHEMT process. The circuit size is 0.88 mm×0.88 mm, which is only about 0.02λ₀×0.02λ₀ at f₀ = 6.85 GHz. To the best of our knowledge, this is the smallest UWB BPF ever reported.