Half-power point

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The half-power point is the frequency at which the output power has dropped to half of its peak value; that is, at a level of -3 dB.[1] The half-power point is a commonly used definition for the cutoff frequency and can be used in a variety of contexts, including the characterization of electronic amplifiers , optical filters,[2].

Amplifiers and filters[edit]

This occurs when the output voltage has dropped to 1/√2 or 0.707 of the maximum output voltage (exact: ) and the power has dropped by half (1/2 or 0.5) (exact: ). A bandpass amplifier will have two half-power points, whilst a low pass amplifier will have only one. A high pass amplifier stage will have only the lower half-power point.

The bandwidth of an amplifier is usually defined as the difference between the lower and upper half-power points. This is therefore also known as the 3 dB bandwidth.


The half-power point of an antenna beam is the angle off boresight at which the antenna gain has fallen 3 dB below the peak. The angle between the 3 dB points is known as the beamwidth.[3]

See also[edit]


  1. ^ "Power bandwidth - MATLAB powerbw". uk.mathworks.com. Retrieved 5 August 2017. 
  2. ^ Schlessinger, Monroe (1995). Infrared technology fundamentals (2nd ed., rev. and expanded. ed.). New York: M. Dekker. ISBN 0824792599. 
  3. ^ Antenna Introduction / Basics (PDF), retrieved 2017-08-08