Filter information & software

Wave Filters

Wave filters are widely used to separate bands of frequencies.

Wave filters can be considered artificial transmission lines with lumped components as shown in these basic wave filter circuit examples:

 Input o-----UUUUUU-----o-----UUUUUU-----o-----UUUUUU-----o Output
L1/2 ¦ L1 ¦ L1/2
¦ ¦
C2 === C2 ===
¦ ¦
¦ ¦
Ground o----------------o----------------o----------------o Ground Input o-------||-------o-------||-------o-------||-------o Output
2C1 ¦ C1 ¦ 2C1
$ $
L2 $ L2 $
$ $
¦ ¦
Ground o----------------o----------------o----------------o Ground

Wave filter component values are chosen to efficiently transmit current from input to output in a desired band of frequencies while more or less completely suppressing transmission of current at all other frequencies. Boundary frequencies between the transmission and suppression frequency bands are called cutoff frequencies.

Wave filters are divided into major classes named low-pass, high-pass, band-pass, and band-elimination according to the frequency bands they are designed to transmit and suppress. (Those classes also are known as lowpass, highpass & bandpass.)

Inductive and capacitive elements of ideal wave filters would be pure reactances, but practical reactive components always have dissipation losses due to resistance, so reactances in practical wave filters are never pure. Element dissipation losses must be kept as small as reasonably practical by constructing wave filters with high-Q components if it is desired to approach ideal wave filter characteristics.

These pages contain technical information and software to assist in the design of band-pass, low-pass and high-pass wave filters:

  • Band-Pass Simple Coil & Capacitor Band-Pass (Bandpass) Filters
  • Low-Pass & High-Pass Simple, Coil & Capacitor, Low-Pass (Lowpass) & High-Pass (Highpass), T & Pi Filters

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