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082-Engineering-Mathematics-Anthony-Croft-Robert-Davison-Martin-Hargreaves-James-Flint-Edisi-5-2017

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4.5 Some simple polar curves 165

u

Antenna

Figure4.19

Electric field strength atafixed distance from the

antenna depends upon the angle θ.

Byconsidering

cos(

r =

π cosθ)

2 ∣ sinθ ∣

we can use a polar curve to depict the field strength at any angle. Graph-plotting

softwareisavailableforproducingpolarplotssuchastheoneshowninFigure4.20,

which shows a typical angle, θ, and itsassociated radiusr.

The radius of the plot for a particular value of θ represents the transmitted field

strengthandsotheantennainFigure4.20hasnoradiationinthehorizontaldirection

and maximum radiation inthe vertical direction.

y

1

0.5

r

u

–0.5 0.5

x

–0.5

–1

Figure4.20

Thetransmitted field strength forthe antenna,

r,varies with the angularposition, θ.

EXERCISES4.5

1 Describethe curve defined byr = 2,0 ◦ θ 90 ◦ . 2 Describethe surfacedefined by0 r2,

30 ◦ θ 45 ◦ .

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