LC Filter Designer

Butterworth and Chebyshev ladder filters, low-pass, high-pass, band-pass and band-stop, order 1 to 9, plus elliptic (Cauer) low-pass and high-pass, order 3 to 7, ideal lossless parts between resistive terminations.

BeginnerExpert

Specify

What should the filter pass?

Pick the shape. The picture shows what it does.

Low-passPasses everything below the cutoff, for example a transmitter harmonic filter.High-passPasses everything above the cutoff, for example to keep broadcast-band signals out.Band-passPasses one band, for example a receiver front end for one ham band.Band-stopNotches out one band, for example a strong local broadcast station.

How sharp should it cut off?

Steeper filters cut off closer to the edge of the passband, at the cost of a little ripple.

Gentle ButterworthFlat passband, slow roll-off.Steeper ChebyshevA little ripple, faster roll-off.Steepest, with notches EllipticRipple in the passband and deep notches just above the cutoff. Fewer parts for the same rejection.

Passband ripple

Specs

Basics

Cutoff (−3 dB)

MHz

Order (1–9)

Source and load R

First element

Load R (optional)

Transmit power (for toroid sizing)

Leave the load blank for equal terminations (even-order Chebyshev then picks the load it needs). Enter a load to design for a different one; a ratio the filter cannot reach is refused with the reason.

Topology

How narrow is it?

Losses

Inductor unloaded Q (core, at f₀)

Q_u

Estimated insertion loss at f₀: coming soon

The finite-Q loss estimate needs an engine update that is still to come, so this field is off for now. The design below uses ideal, lossless parts.

Schematic

Response

FullPassband zoom

LogLinear

Hover or tap the plot to read values. When the plot has focus, arrow keys step along the curve.

Parts

Parts list
Ref	Position	Exact	E12	E12 error	E24	E24 error	Core	Mix	Turns	Actual L	L error	Flags

Building it with real parts

These values assume ideal, lossless parts. Real inductors have finite Q, which adds passband loss and rounds the Chebyshev ripple, so use the highest-Q inductors practical (for example powdered-iron toroids of a mix suited to the frequency). Use stable, low-loss capacitors such as C0G/NP0 ceramic or silver mica, with a voltage rating of about twice the peak RF voltage across them. In a transmitter harmonic filter, that voltage is set by the power level and impedance.

Inductors can be wound with the Toroid Turns calculator.

Sources & verification

Values come from the closed-form Butterworth and Chebyshev prototype equations, and the response is an ABCD analysis of ideal, lossless parts. The math was independently checked against these published tables: RF Cafe, “Butterworth Filter Lowpass Prototype Element Values” (Butterworth, n = 1–9); RF Cafe, “Chebyshev Filter Lowpass Prototype Element Values” (Chebyshev 0.01, 0.1, 0.2 and 0.5 dB, n = 2–9); Steer, “Butterworth and Chebyshev Filters”, Microwave and RF Design IV: Modules, LibreTexts §2.07 (Chebyshev 1 dB, n = 3, 5, 7); IVARC filter article, version 2, Tables A2 and A3 (Chebyshev 1 dB, n = 3 and 4, including the even-order load). The engine is also checked against ngspice across a test sweep (orders 1–9, Butterworth and Chebyshev 0.01–1 dB, LP/HP, both forms). Elliptic (Cauer) designs follow Zverev, Handbook of Filter Synthesis (1967), §5.8. Engine: .