# Transmission Lines and Antennas Dec.09/Jan.2010

Note: Answer any FIVE full questions, selecting at least TWO questions from each part

PART-A

1    a. Derive the expressions for cut-off frequency and characteristic impedance of constant-K low pass filter-T section.

b.   Derive the expression for velocity of propagation in case of ordinary telephone cables.

c.   Draw the standing waves diagram on a line having open-or-short circuit termination and define nodes.

2    a. Derive the necessary condition for distortion less line.

b.  Why must impedance (or admittances) be normalized before being plotted on a standard Smith chart?

c.   Why are short circuit stub preferred to open circuited ones?

3    a. Explain the following terms as related to antennas :

i) Beam width          ii) Bandwidth             iii)Gain

b.  Prove that beam efficiency plus stray factor is equal to unity.

c.   Find the power density at a distance 3 km from an isotropic source, if the power density at a distance 2 km is 10m watts/ sq.units.

3  Write notes on :

a.   Antenna field zones

b. Quarter wave line

c. Reflection loss

PART-B

5    a. Derive the total field expression in case of two isotropic sources are with same amplitude and opposite phase. Plot the relative field pattern when these two isotropic sources are spaced by A apart.

b.  Find the directivity for the source with radiation intensity variation U = Umsin0 sin2(|) where 0 and (|) range between 0 and tt.

c.   Illustrate the principle of pattern multiplication with suitable example.

6  a. Derive the expressions for instantaneous electric and magnetic field at a large distance V from a loop antenna of radius ‘a’.

b.  A half wave dipole radiating in free space is driven by a current of 0.5 amps at the terminals. Calculate the electric field strength ‘E’ at a distance 1 km from the antenna at angles 45° and 90°.

c.   Using the relevant equations, justify : “A helical antenna can be used as polarization diversity system”.)

7 a. Describe design considerations of log-periodic array.

b. A 64-mt diameter dish antenna operating at a frequency of 1.43 GHz is fed by a non- directional antenna. Calculate its :

i) HPBW              ii) BWFN

iii) Gain with respect to dipole with even illumination.

C  Illustrate working principles of non-metallic dielectric lens antenna.

8. Write short notes on :

a. Ultra wide band antennas

b. Patch antenna

c. Embedded antenna.