# VTU Question Paper BE EC 6th Sem Antenna and Propagation Jan 10

**Set-A **

**PART-A**

1 a. Define the term antenna aperture. Derive the equation for receptivity in terms of aperture.

b. Explain the following terms with respect to antenna:

i) Field zones ii) Effective height.

c. A lossless resonant X/2 dipole antenna having an input impedance of 73 Q is to be connected to a transmission line having characteristic impedance of 50 Cl. The pattern of the antenna is 5 given by u – u_{0}Sin 0. Find the overall gain of the antenna,

2 a. For %/2 dipole antenna derive an expression for effective aperture and obtain

the value of directivity.

b. State and explain power theorem and its application to point sources.

c. For a source having radiation intensity u~ u_{m} SinO Sin^{2}<j>, find the directivity by i) Exact method; ii) Approximate method.

3 a. Prove that the width of main lobe of uniform end-fire array is broader than

that for a uniform broad side array.

b. Explain the principle of pattern multiplication.

c. Obtain the field pattern for a linear uniform array of 6 isotropic point sources spaced X/2 distance apart. The power is applied with equal amplitude and in phase. Also find HPBW andFNBW.

4 a. Derive far-field equations for a thin linear center fed antenna of length L.

b. A thin linear dipole antenna is X/12 long and its loss resistance is 1.2 Cl. Find the radiation resistance and efficiency.

c. Write notes on i) Rhombic antenna ii) Folded dipole antenna.

**PART-B**

5 a. Considering general case derive the far field equations for loop antenna.

b. Explain Babinet’s principle with illustration.

c. Derive the equation for impedance of a slot antenna in terms of the impedance of the complementary dipole antenna.

6 a. Explain the following design parameters of a helical antenna :

i) Beam width

ii) Axial ratio

iii) Impedance.

b. Explain in detail the log-periodic dipole array.

c. Write notes on i) Antennas for ground penetrating radar ; ii) Ultra wide band antennas.

7 a. A free space line of sight microwave link operating at 10 GHz consists of a transmit an receive antenna each having a gain of 25 dB. The distance between the two antennai 30 kmt and the power radiated by the transmit antenna is 10 W. Calculate the path loss the link and the received power.

b. An antenna located at the surface of the earth is used to receive the signals transmitted another antenna located at a height of 80 mt from the spherical surface of the earth (mi radius = 6370 kmts). Calculate the optical and radio horizon if dN/dh = -39 / kmt. (06 Mai

c. In troporpheric propagation, show that radius of curvature of path is a function of the rate change of dielectric constant with height and explain the duct propagation of wave.

8 a. For ionospheric layers, derive the expression for conductivity and relative permittivity a function of electron density and angular frequency.

b. Define the terms

i) Critical frequency f_{c}

ii) Skip distance Dskip

iii)Maximum usable frequency fMUF*

iv) Obtain the relation for skip distance in terms of fand fMUF-

c. Ionospheric wave is reflected from E layer with virtual height 100 kmt and from F layer v\ virtual height 300 kmt. Determine the single loop distance for each layer.