A25-cm-long, center-fed, wire-type antenna is made of copper wire (nonmagnetic, σcu = 5.8×107 s/m) with a radius of 1 mm. the antenna is excited by a sinusoidal current with an amplitude i0 = 5 a. determine the antenna gain (in db) and the time average power radiated, if the frequency is

(a) 1 mhz,
(b) 0.6 ghz.
(c) at what operating frequency the given antenna is more efficient and what is the ratio (in db) of powers emitted at 0.6 ghz and 1 mhz?

(a) 6.85 mw (b) 915 W (c) more efficient at higher frequencies

Explanation:

(a) At 1 MHz

λ = c / f = = 300 m

λ / l = 300 / 0.25 = 1200, hence this is short dipole

From prad = - equation (I)

Solving for I0 = 5A,

we obtain prad = 6.85 mw

(b) At 0.6 GHz

Hence λ = c / f =

Likewise, substituting into equation (I)

prad = 915 w

(c) At higher frequency as seen in the previous two solutions, the antennae radiates 915/6.85 mw = 133500.8 times as much power as it does at lower frequency.

Hence, it is more efficient at higher operating frequency

answer:

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explanation: