Download AKTU (Dr. A.P.J. Abdul Kalam Technical University (AKTU), formerly Uttar Pradesh Technical University (UPTU) B-Tech 5th Semester (Fifth Semester) 2017-2018 NEC 504 Antenna And Wave Propagation Question Paper
Paper ID23053
B. TECH. (REGULAR & CARRY OVER)
(SEM. V) THEORY EXAMINATION 2017-2018
ANTENNA AND WAVE PROPAGATION
Time: 3 Hours Total Marks:100
N0te:Attempt all questions. If require any missing data; then choose suitably.
SECTION A
1. Attempt all questions in brief. 2 x 10 = 20
(a) Explain half power beam width and first null beam width.
(b) Explain the concept of point sources.
((3) Explain antenna temperature in brief.
(d) What is tapering? Explain it with suitable example.
(6) The radiation resistance of an antenna is 72 Q and loss resistance is 8 Q. What
isthe directivity in dB if the power gain is 16.
(f) A uniform linear array consists of 20 isotropic point sources with a spacing of M4
if the phase difference is ?90?. Calculate its HPBW and directivity.
(g) For a parabolic re?ector having directivity 0f 30 dB and an aperture efficiency of
55 % operating at 15 MHz.Calculate the area of parabolic re?ector and HPBW.
(h) Find the power gain and directivity of a horn whose dimensions are 10 cm X 5 cm
and operating at a frequency of 6 GHz.
(i) Define skip distance and virtual height.
(j) A microwave signal of 1.9 GHz arrives at an antenna Via two paths differing in
length by 19 m. Calculate (i) the difference in arrival time for the two paths (ii)
phase difference between the two signals.
SECTION B
2. Attempt any three of the following: 10 x 3 = 30
(a) What is Antenna gain, Directivity, Beam efficiency, and Antenna Impedance?
(b) Explain the linear array of n isotropic point sources of equal amplitude and
spacing. Derive the expressions of direction of pattern maxima, direction of
minimum field pattern, beam width of major lobe and directivity for a broadside
array of n isotropic sources.
((3) Derive the expressions of potential, electric and magnetic field of a short electric
dipole.
((1) Describe the principle of direction finding by means of a closed loop antenna and
give the expression for the induced voltage and field strength for short 100p and
large 100p.
(e) Explain the following-
(i) Atmospheric noise
(ii) Maximum usable frequency
(iii) Critical frequency
(iv) Skip distance in a short wave communication
SECTION C
Attempt any two of the following: 5 x 2 = 10
(a) Explain the antenna efficiency. A directional antenna has an effective radiated
power of 1.1 kW, when it is fed with a terminal input power of 90 W. Radiation
resistance is 74 Q at resonance and measured antenna current is 1.088 ampere
rms. Find (1) The antenna efficiency, (ii) The antenna power loss, (iii) The
directive gain in decibels over an isotropic radiator.
(b) Write short notes on the following-
(i) Directivity and Resolution.
(ii) The Radio Communication Link
((3) Explain the antenna aperture in detail and also derive an expression showing the
relation between effective aperture and directivity of an antenna.
Attempt any two of the following: 5 x 2 = 10
(a) Derive the total far field for an array of two isotropic point sources of equal
amplitude and phase. Find out the maximum, minimum and half power point
directions of radiation pattern for this case.
(b)What is Yagi-Uda Antenna? Explain its construction and properties with special
reference to directivity and bandwidth.
((3) Explain the Thin Linear Antenna and also derive the radiation resistance of M2
antenna.
Attempt any two of the following: 5 x 2 = 10
(a)What is helical antenna and explain different type of feed method for parabolic
re?ector.
(b) Write the short note on log periodic antenna with proper mathematical expression.
((3) Explain the slotantenna used in communication with its application.
Attempt any two of the following: 5 x 2 = 10
(a) What are the two modes of radio propagation? Discuss the space wave
propagation.
(b) What do you understand by plane earth re?ection? Derive the formulas of
re?ection coefficient for horizontal polarization and re?ection coefficient for
vertical polarization.
(0) What is the role of ionosphere in propagation? How do re?ection and refraction
Occur?
Attempt any two of the following: 5 x 2 = 10
(a)EXplain the principle of pattern multiplication. Synthesize the pattern using this
principle for the two cases- (i) Four isotropic elements spaced M2 apart and fed in
phase. (ii) Eight isotropic elements spaced M2 and fed in phase.
(b) Define Directive gain and power gain in detail and also explain the difference
between them.
((3) How a horn antenna produces a uniform phase front with a large aperture in
comparison to waveguide? Mention one antenna system when a horn is used as a
feed system.
This post was last modified on 29 January 2020