RegisterSpatial period, spatial frequencyIn time domain, the term period denoted the shortest time distance (time interval, [s]) of two moments, when phase of harmonic oscillation differs for 2π. In spatial domain, the shortest distance [m] of two points, where phase differs for 2π is denoted as spatial period. In Figure, plane wave propagation is depicted, and three planar equiphase surfaces, which are perpendicular to the wave propagation, are shown. The symbol T denotes the spatial period in the direction of propagation, and symbols Tx and Ty denote spatial periods in directions of coordinate axes x and y. Unit of the spatial period is [meter]. In the direction of propagation, spatial period equals to the wavelength λ. Inverted value of the spatial period is spatial frequency: f = 1/T,fx = 1/Tx a fy = 1/Ty (in the direction of propagation, in the direction x and in the direction y). The unit is 1/m. Considering Figure, we can see 2πf= ω = 2π /T= 2π/λ = k (wave-number in the direction of propagation), and similarly 2π fy = wy = ky (wave-number in the direction y). Since ky = k cos( j), spatial frequency depends od the direction of propagation. Back
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