Quadrature

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Quadrature, derived from Latin quadrare, may refer to:

In signal processing:

• Quadrature amplitude modulation (QAM), a modulation method of using both a carrier wave and a 'quadrature' carrier wave that is 90° out of phase with the main carrier
• Quadrature phase, oscillations that are said to be in quadrature if they are separated in phase by 90° (π/2, or λ/4)
• Quadrature filter, the analytic signal of a real-valued filter
• Quadrature coupler, see under chapter five in Power dividers and directional couplers

In mathematics:

• Quadrature of the circle (also squaring the circle), in geometry, the problem of constructing a square and circle of equal area, impossible using only an unmarked straight-edge and compass
• Summing in quadrature means summing the squares of numbers, then taking the square root, as used in error analysis
• Numerical integration, the numerical calculation of the area under a curve, or more generally, using numerical integration to calculate a definite integral
• The Quadrature of the Parabola, a treatise by Archimedes
• Gaussian quadrature, a special case of numerical integration, named after Carl Friedrich Gauss

Quadrature may also refer to:

• In motion control, quadrature encoder is a rotary encoder or linear encoder giving both the relative position and the direction of motion of a shaft
• In astronomy, quadrature occurs when two celestial bodies appear 90° apart from one another as viewed from a third celestial body. As an example, the Moon and the Sun are in quadrature with respect to the Earth when the Moon is in its exact first quarter or last quarter phases. The symbol for astronomical quadrature is a hollow square

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