Antenna Directivity(天线的方向性)

    Radiation profile (angular dependence of the Poynting flux = directivity) can be varied by a suitable choice of the number of antennas in an array and the phase angle between neighbouring radiation fields. The direction of radiation beam can be rotated electronically without physically rotating the array. The first animation shows radiation profile of 4-antenna array with equal spacing of half wavelength. Rotation of the radiation pattern is controlled by the phase angle phi.

N = 4, d = lambda/2

As the number of antennas increases, the radiation profile becomes sharper. Animation below shows the case of 20- antenna array with neighbouring separation of half wavelength.

N = 20, d = lambda/2

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