Question:
(a) A uniform linear array consists of 20 vertical dipoles, each spaced by half a wavelength in the horizontal plane.
(i) If all array elements are fed in phase, what is the direction of the main beam and what is the (maximum) electric field strength in this direction compared with that of a single antenna?
(ii) What phase difference should be introduced between adjacent dipoles to produce:
[1] an endfire array?
[2] a main beam maximum at 10 degrees to broadside?
[3] a main beam maximum at 70 degrees to broadside?
(iii) If for the endfire configuration, the frequency of the received signal is increased by 10% without changing the physical distance or the phase difference between adjacent dipoles, by what angle will the direction of the main beam be deviated?
(b) An electric field strength of 10 µV/m is to be measured at an observation point θ = π/2, 500 km away from a half wave dipole, operating in air at 50 MHz.
(i) Determine the length of the dipole.
(ii) Evaluate the current that must be fed to the antenna.
(iii) Determine the average power radiated by the antenna.