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

the equation above shows how temperature f, measured in degrees fahrenheit, relates to a temperature c, measured in degrees celsius. based on the equation, which of the following must be true?

a temperature increase of 1 degree fahrenheit is equivalent to a temperature increase of

5

9

degree celsius.

a temperature increase of 1 degree celsius is equivalent to a temperature increase of 1.8 degrees fahrenheit.

a temperature increase of

5

9

degree fahrenheit is equivalent to a temperature increase of 1 degree celsius.

a) i only

b) ii only

c) iii only

d) i and ii only

answer:

a

explanation: