ElectroMagnetic Theory Concepts & Solved Numericals

3) A certain antenna with an efficiency of 95% has maximum radiation intensity of 0.5 W/sr. Calculate its directivity when (a) The input power is 0.4 W (b) The radiated power is 0.3 W SOLUTION: a) P rad = η r P in = (0.95) (0.4) = 0.38 4) Evaluate the directivity of an antenna with normalized radiation intensity SOLUTION: 5) Determine the maximum effective area of a Hertzian dipole of length 10 cm operating at 10 MHz. If the antenna receives 3 µW of power, what is the power density of the incident wave? SOLUTION: For the hertzian dipole, G d = 1.5 sin 2 θ By definition, P r = A e P ave

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 Z o = 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) R rad = 73 Ω (For λ/2 (Half Wave) Dipole Antenna) R rad = 36.56 Ω (For λ/4 Monopole Antenna) d) Standing Wave ratio (S)      Z L = 73 + j42.5 (For Half wave dipole Antenna)      Z L = 36.5 + j21.25 (For λ/4 Monopole Antenna) 2) Calculate the directivity of a) The Her...

This page contains basic questions and short notes on some of the keywords on antenna theory: 11) What is meant by Polarization? The polarization of the radio wave can be defined by direction in which the electric vector E is aligned during the passage of atleast one full cycle.Also polarization can also be defined the physical orientation of the radiated electromagnetic waves in space. The polarization are three types. They are Elliptical polarization ,circular polarization and linear polarization. 12) What is meant by front to back ratio? It is defined as the ratio of the power radiated in desired direction to the power radiated in the opposite direction. i.e FBR = Power radiated in desired direction / power radiated in the opposite direction. 13) Define antenna efficiency? The efficiency of an antenna is defined as the ratio of power radiated to the total input power supplied to the antenna. Antenna efficiency = Power radiated / Total input Power 14) What is radi...

This page contains basic questions and short notes on some of the keywords on antenna theory: 1) Define an antenna? Antenna is a transition device or a transducer between a guided wave and a free space wave or vice-versa. Antenna is also said to be an impedance transforming device. 2) What is meant by radiation pattern? Radiation pattern is the relative distribution of radiated power as a function of distance in space .It is a graph which shows the variation in actual field strength of the EM wave at all points which are at equal distance from the antenna. The energy radiated in a particular direction by an antenna is measured in terms of FIELD STRENGTH. (E Volts/m) 3) Define Radiation intensity? The power radiated from an antenna per unit solid angle is called the radiation intensity U (watts per steradian or per square degree). The radiation intensity is independent of distance. 4) Define Beam efficiency? The total beam area (WA) consists of the main beam area (...