half-power point

A simple formula for the beam width, measured between half-power points (), is:

This decrease in power is often specified to be the half-power points, i.e., 3 dB below the maximum power.

At 20 and 6cm this error is purely linearly polarised (there is no circularly polarised component), whereas at 13 and 3cm the circularly polarised component is somewhat less than 1% at the half-power point.

Because the electrical beam width was 4 degrees (to the -3db or half-power points), the target would be smeared across a portion of a cylinder, so as to be wider in bearing than in range (i.e., on the order of 4 degrees, rather than 0.06 degrees implied by the mechanical pointing accuracy), for distant targets.