// Calculators › Filter Design

LC Filter Design

Design Butterworth, Chebyshev and Bessel LC ladder filters — lowpass, highpass, bandpass and bandstop. Get exact component values, a schematic, and a frequency response plot.

// How to use this tool
1
Choose filter type — Lowpass, Highpass, Bandpass or Bandstop.
2
Choose response — Butterworth: maximally flat. Chebyshev: sharper rolloff with equiripple. Bessel: linear phase / constant group delay.
3
Set order — higher order = steeper rolloff. Each order adds −20 dB/decade. Max 9 elements.
4
LP/HP: enter cutoff frequency. BP/BS: enter centre frequency f0 and 3 dB bandwidth.
5
Set Z0 — typically 50 Ohm for RF.
6
Click Design Filter — schematic, response and component table appear instantly.
// Filter Parameters
dB
3
prototype elements
(max 9)
Ohm
Please check your inputs.
BP/BS -3 dB edges: fL,H = sqrt(f0^2 + (BW/2)^2) minus/plus BW/2
Butterworth rolloff: -20n dB/decade past cutoff
Lk = gk * Z0 / wc Ck = gk / (Z0 * wc)
// LC Ladder Schematic
🔌
Set parameters and click Design Filter
// Frequency Response
📈
Response will appear here
// Component Values
⚙
Components will appear here

About the LC Filter Design Calculator

LC filters use inductors and capacitors arranged in a ladder network to pass signals in a desired frequency band while rejecting others. They are used throughout RF and audio systems as anti-aliasing filters, image rejection filters, harmonic filters on transmitter outputs and channel selection filters in receivers.

Filter Response Types

Butterworth filters are maximally flat in the passband — the frequency response has no ripple and falls off smoothly. The rolloff is -20n dB per decade where n is the filter order. Chebyshev filters trade passband ripple for a steeper rolloff. A 3rd-order Chebyshev with 0.5 dB ripple has significantly better stopband rejection than a 3rd-order Butterworth. Bessel filters are optimised for constant group delay rather than sharp rolloff — they preserve the shape of modulated signals because all frequency components are delayed by the same amount.

Filter Order and Rolloff

Each additional filter order adds approximately -20 dB per decade to the rolloff rate and one reactive component to the circuit. A 3rd-order Butterworth has -60 dB per decade rolloff. A 7th-order Chebyshev with 0.1 dB ripple can achieve over 100 dB rejection at twice the cutoff frequency. Higher order means sharper rolloff but also more components, higher insertion loss and tighter tolerances.

Bandpass and Bandstop Transformation

Lowpass prototype filters are transformed to bandpass and bandstop responses using frequency substitution. Each lowpass element becomes a series LC pair (for bandpass) or parallel LC pair (for bandstop). The bandwidth of the transformed filter matches the specified 3 dB bandwidth, and the centre frequency shifts to f0.