SOLVED Numerical's - Antenna Theory - Page 1.




1) An electric field strength of 10 µV/m is to be measured at an observation point θ = π/2, 500 km from a λ/4 monopole antenna operating in air at 50 MHz.
(a) What is the length of the dipole?
(b) Calculate the current that must be fed to the antenna.
(c) Find the average power radiated by the antenna.
(d) If a transmission line with Zo = 75 Ω is connected to the antenna, determine the standing wave ratio.


SOLUTION:

a) The wavelength λ = c / f =( 3 x 108) / (50 x 106) = 6 cm.

                             Length Of The Dipole (l) = λ/4 = 6 / 4 = 1.5 cm.


b)



c)

Rrad = 73 Ω (For λ/2 (Half Wave) Dipole Antenna)

Rrad = 36.56 Ω (For λ/4 Monopole Antenna)



d)

Standing Wave ratio (S)




     ZL = 73 + j42.5 (For Half wave dipole Antenna)

     ZL = 36.5 + j21.25 (For λ/4 Monopole Antenna)




2) Calculate the directivity of
a) The Hertzian monopole
b) The quarter-wave monopole



SOLUTION:

a)
For the hertzian monopole



b)

  For the quarter-wave (λ/4) monopole



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