What is the frequency response of a T-network with series capacitors and a shunt inductor?
Why In a ladder filter the series elements decide what gets through and the shunt elements decide what gets dumped to ground. Capacitive reactance (Xc = 1/(2πfC)) falls as frequency rises, so series capacitors pass high frequencies and block low ones, while the shunt inductor's reactance (XL = 2πfL) is small at low frequencies and shorts them to ground. Both actions favor the high end, so this T-network is a high-pass filter.
Watch out Low-pass is the mirror image network: series inductors with a shunt capacitor. Band-pass and notch responses require resonant (L and C together) branches, which a single-reactance-per-branch T-network does not have.
Series C and shunt L = highs pass. Flip the parts (series L, shunt C) and you get low-pass.