Figure 218 Vertical Beamwidth Showing Half Power Points

OrnnkJireclional Antenna

^ Hal-Power Points

fuWj

Hair-Power Points

30= Vertical BaamwHIfl

30= Vertical BaamwHIfl

Spillover

Main lobe is Hi® a doughnut with Ihe anle-nna in Ihe 'hole'

stoe VIEW

Remember from the discussion of wireless spillover that wireless power does not stop and start exactly along a straight line but declines gradually with distance; therefore, a consistent method is needed to de fine the wid th of tVe mgi n lobe. This meth od is vi sible in Figureu 2-17 and 2-18. The smooth outlines of the main lobes show the approximate intensity of the wireless power at various distances away fro m the antenna, bu t the dotted lines in side the smooth lines enclose most of the power of the main lobe. These dotted lines pass through the half-power points —the points on each side of the ce nter 8f the m ain lobe wh ere th e wireless pow er is one-half as strong as it is at the center of tme lobe. The angle between the two dotted lines defines the horizontal or vertical beamwidth of the antenna.

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