CONTROL SYSTEMS

Code No: R05220205 Set No. 1
II B.Tech II Semester Regular Examinations, Apr/May 2008
CONTROL SYSTEMS
( Common to Electrical & Electronic Engineering, Electronics &
Communication Engineering, Electronics & Instrumentation Engineering,
Electronics & Control Engineering, Electronics & Telematics and
Electronics & Computer Engineering)
Time: 3 hours Max Marks: 80
Answer any FIVE Questions
All Questions carry equal marks
⋆ ⋆ ⋆ ⋆ ⋆
1. (a) Explain the traffic control system concepts using open loop as well as closed
loop system.
(b) Why is negative feedback invariably preferred in closed loop systems? [8+8]
2. (a) Reduce the given block diagram (figure 2a)and hence obtain the transfer func-
tion C(s)
R(s) .
Figure 2a
(b) Explain the need of signal flow graph representation for any system. [10+6]
3. (a) What is meant by time response? Explain about
i. Steady- state response
ii. Transient response
(b) A unity feed-back system is characterized by an open loop T.F G(s) = K
s(s+10)
Determine the gain K so that the system will have a damping ratio of 0.5. For
this value of K , determine Ts, Tp and Mp for a unit step input. [6+10]
4. (a) Define the term root locus and state the rule for finding out the root locus on
the real axis?
(b) Calculate the angle of asymptotes and the centroid for the system having
G(s)H(s) = K(s+3)
s(s+2)(s+4)(s+5)
(c) For G(s)H(s) = K
s(s+1)(s+3) , find the intersection point of the root locus with
the jω - axis? [4+6+6]
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Code No: R05220205 Set No. 1
5. Sketch the Bode plots for a system
G(s) = 15(s+5)
s(s2+16s+100)
Hence determine the stability of the system. [16]
6. Write short notes:
(a) Comparision of polar & Nyquist plots
(b) Applications of Nyquist criterion. [8+8]
7. (a) What is compensation? what are the different types of compensators?
(b) What is a lag compensator, obtain the transfer function of lag compensator
and draw pole-zero plot?
(c) Explain the different steps to be followed for the design of compensator using
Bode plot? [3+3+10]
8. Obtain the two differential state representation for the system with transfer func-
tion.
y(s)
u(s) = 2
S3+6S2+11S+6 . [16]
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Code No: R05220205 Set No. 2
II B.Tech II Semester Regular Examinations, Apr/May 2008
CONTROL SYSTEMS
( Common to Electrical & Electronic Engineering, Electronics &
Communication Engineering, Electronics & Instrumentation Engineering,
Electronics & Control Engineering, Electronics & Telematics and
Electronics & Computer Engineering)
Time: 3 hours Max Marks: 80
Answer any FIVE Questions
All Questions carry equal marks
⋆ ⋆ ⋆ ⋆ ⋆
1. (a) Define transfer function and what are its limitations? [6+10]
(b) Find the transfer function of the following system: Shown in figure 1b.
Figure 1b
2. (a) Reduce the given block diagram (figure 2a) and hence obtain the transfer
function C(s)
R(s)
Figure 2a
(b) Explain the working principle of synchro receiver with neat sketch. [10+6]
3. (a) What are generalized error constants? State the advantages of generalized
error coefficients?
(b) For a first order system, find out the output of the system when the input
applied to the system is unit ramp input? Sketch the r(t) and c(t) and show
the steady state error. [8+8]
4. (a) What are the necessary conditions to have all the roots of the characteristic
Equation in the left half of s-plane?
(b) What are the difficulties in RH stability crititerion? Explain ,how you can
over come them? [4+12]
5. (a) State the advantages & limitations of frequency domain analysis
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Code No: R05220205 Set No. 2
(b) Sketch the Bode plot s of
G(s) = 28.5e−0.1s
s(1+s)(1+0.1s)
Hence find gain cross over frequency. [6+10]
6. (a) What is “Nyquist Contour”?
(b) A system is given by
G(s) = 4s+1
s2(s+1)(2s+1) Sketch the Nyquist plot & hence determine the stability
of the system. [2+14]
7. (a) What is compensation? what are the different types of compensators?
(b) What is a lag compensator, obtain the transfer function of lag compensator
and draw pole-zero plot?
(c) Explain the different steps to be followed for the design of compensator using
Bode plot? [3+3+10]
8. Obtain the two differential state representation for the system with transfer func-
tion.
y(s)
u(s) = 2
S3+6S2+11S+6 . [16]
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Code No: R05220205 Set No. 3
II B.Tech II Semester Regular Examinations, Apr/May 2008
CONTROL SYSTEMS
( Common to Electrical & Electronic Engineering, Electronics &
Communication Engineering, Electronics & Instrumentation Engineering,
Electronics & Control Engineering, Electronics & Telematics and
Electronics & Computer Engineering)
Time: 3 hours Max Marks: 80
Answer any FIVE Questions
All Questions carry equal marks
⋆ ⋆ ⋆ ⋆ ⋆
1. (a) Write the important differences between open loop and closed loop systems
with suitable examples.
(b) Obtain the transfer function X0(s)
X1(s) of the following system. Shown in figure 1b.
[8+8]
Figure 1b
2. (a) State and explain mason’s gain formula for the signal flow graph.
(b) What are differences between block diagram reduction and signal flow graph
reduction? [8+8]
3. (a) How steady ?state error of a control system is determined? How it can be
reduced?
(b) Determine the error coefficients and static error for G(s) = 1
s(s+1)(s+10) ,
H(s) = s + 2 . [8+8]
4. (a) What are the necessary conditions to have all the roots of the characteristic
Equation in the left half of s-plane?
(b) What are the difficulties in RH stability crititerion? Explain ,how you can
over come them? [4+12]
5. (a) Define frequency response.
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Code No: R05220205 Set No. 3
(b) Discuss the advantages & disadvantages of frequency response analysis.
(c) Bring out the correlation between time response & frequency response and
hence show that the correlation exists for the range of damping ratio 0 <ζ< 0.707.
[2+6+8]
6. (a) What is “Nyquist Contour”?
(b) A system is given by
G(s) = 4s+1
s2(s+1)(2s+1) Sketch the Nyquist plot & hence determine the stability
of the system. [2+14]
7. Design a lead compensator for unity feed back system whose open loop transfer
function G(S) = K
S(S+1)(S+5) to satisfy the following specifications.
(a) velocity error constant KV  50
(b) Phase margin  200. [16]
8. (a) Obtain the state model of the system whose transfer function is given as.
Y (s)
V (s) = 10
S3+4S2+2S+1
(b) Consider the matrix A compute eAt? [8+8]
A =  0 1
−2 − 3 
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Code No: R05220205 Set No. 4
II B.Tech II Semester Regular Examinations, Apr/May 2008
CONTROL SYSTEMS
( Common to Electrical & Electronic Engineering, Electronics &
Communication Engineering, Electronics & Instrumentation Engineering,
Electronics & Control Engineering, Electronics & Telematics and
Electronics & Computer Engineering)
Time: 3 hours Max Marks: 80
Answer any FIVE Questions
All Questions carry equal marks
⋆ ⋆ ⋆ ⋆ ⋆
1. (a) Explain the basic components of control systems?
(b) Find the transfer function for the system given figure 1b:
Figure 1b
where, M is the mass of the system. [6+10]
K is the spring deflection
B is the coefficient of viscous damping.
2. (a) Reduce the given block diagram (figure 2a) and hence obtain the transfer
function C(s)
R(s)
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Code No: R05220205 Set No. 4
Figure 2a
(b) Explain the need of Mason’s gain formula for any system reduction. [10+6]
3. (a) Define type and order of a control system and hence find the type and order
of the following systems?
i. G(s)H(s) = 100
s(s2+4s+200)
ii. G(s)H(s) = 200
s2(s2+10s+200)
iii. G(s)H(s) = 4(s2+10s+100)
s(s+3)(s2+2s+10)
iv. G(s)H(s) = 200
(1+01s)(1+0.5s)
(b) The unit step response of a second order linear system with zero initial state
is given by c(t) = 1 + 1.25e−6tSin(8t − tan−1 1.333). Determine the damping
ratio, un damped natural frequency of oscillations and peak overshoot? [8+8]
4. (a) Define the the following terms
i. absolute stability
ii. marginal stability
iii. conditional stability
(b) By means of RH criterion determine the stability of the system represented
by the characteristic equation S4 + 2S3 + 8S2 + 4S + 3 = 0
(c) State the advantages of RH Stability criterion? [6+6+4]
5. (a) Derive the expressions for resonant peak & resonant frequency and hence
establish the correlation between time response & frequency response.
(b) Given ζ = 0.7 & ωn = 10 r/s find resonant peak, resonant frequency & Bandwidth.
[10+6]
6. (a) With respect to a function q(s) “Every s-plane contour which does not pass
through any singular points of q(s) has a corresponding contour in q(s) plane”
Elaborate.
(b) What is the effect of adding a zero at origin to the to the open loop transfer
function on polar plot? [8+8]
7. (a) What is compensation? what are the different types of compensators?
(b) What is a lag compensator, obtain the transfer function of lag compensator
and draw pole-zero plot?
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Code No: R05220205 Set No. 4
(c) Explain the different steps to be followed for the design of compensator using
Bode plot? [3+3+10]
8. (a) The system is represented by the differential equation
y¨+ 5y˙ + 6y = u
Find the transfer from state variable representation.
(b) Consider the RLC network shown in figure 8b. Write the state variable representation.
[16]
Figure 8b
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ANALOG COMMUNICATIONS

Code No: R05220405 Set No. 1
II B.Tech II Semester Regular Examinations, Apr/May 2008
ANALOG COMMUNICATIONS
( Common to Electronics & Communication Engineering and Electronics &
Telematics)
Time: 3 hours Max Marks: 80
Answer any FIVE Questions
All Questions carry equal marks
⋆ ⋆ ⋆ ⋆ ⋆
1. (a) With necessary expressions, waveforms and spectrums, Explain AM for an
arbitrary baseband signal m(t).
(b) The output power of an AM transmitter is 1KW when sinusoidally modu-
lated to a depth of 100%. Calculate the power in each side band when the
modulation depth is reduced to 50%. [10+6]
2. (a) Draw the circuit diagram for balanced ring modulator and explain its operation
indicating all the waveforms and spectrums.
(b) In an AM-SC system, modulating signal is a single tone sinusoid 4 cos 2 103t,
which modulates a carrier signal 6 cos 2106t. Write the equation of modu-
lated wave. Plot the two sided spectrum of the modulated wave. Calculate
the amount of power transmitted. [8+8]
3. (a) Describe the time domain band-pass representation of SSB with necessary
sketches.
(b) Find the percentage of power saved in SSB when compared with AM system.
[12+4]
4. (a) Explain the operation of the balanced slope detector using a circuit diagram
and draw its response characteristics. Discuss in particular the method of
combining the outputs of the individual diodes. In what way is this circuit an
improvement on the slope detector and in turn what are the advantages?
(b) Compute the bandwidth requirement for the transmission of FM signal having
a frequency deviation 75 KHz and an audio bandwidth of 10KHz. [12+4]
5. Explain how S/N ratio is a figure of merit incase of performance of a communication
channel. [16]
6. (a) Draw the block diagram of an SSB - SC transmitter employing sideband sup-
pression filter and explain.
(b) Why are limiters and preemphasis filters used in FM radio. [16]
7. (a) With the aid of the block diagram explain TRF receiver. Also explain the
basic superheterodyne principle.
(b) List out the advantages and disadvantages of TRF receiver. [16]
8. (a) Describe the synchronization procedure for PAM, PWM and PPM signals.
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Code No: R05220405 Set No. 1
(b) Discuss about the spectra of PWM and PDM signals. [16]
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Code No: R05220405 Set No. 2
II B.Tech II Semester Regular Examinations, Apr/May 2008
ANALOG COMMUNICATIONS
( Common to Electronics & Communication Engineering and Electronics &
Telematics)
Time: 3 hours Max Marks: 80
Answer any FIVE Questions
All Questions carry equal marks
⋆ ⋆ ⋆ ⋆ ⋆
1. (a) What are the main objectives of a communication system design? What are
the primary resources of any communication system.
(b) The RC load for a diode envelope detector consists of a 1000 pF capacitor
in parallel with a 10-K
 resistor. Calculate the maximum modulation depth
that can be handled for sinusoidal modulation at a frequency of 10 KHz if
diagonal peak clipping is to be avoided.
(c) A broadcast AM transmitter radiates 50 KW of carrier power. What will be
the radiated power at 85 % of modulation and what is the side band power?
[6+6+4]
2. Considering the modulating and carrier waves as sinusoids, Explain the single tone
modulation and demodulation of DSB-SC wave with necessary expressions, wave-
forms and spectrums and explain how only one side band is necessary for transmis-
sion of information. [16]
3. A synchronous detection of SSB signal shows phase and frequency discrepancy.
ConsiderS(t) =
N
P
i=1
cos [(ωct) cos(ωit + i) − sin(ωct) sin(ωit + i)]is an SSB signal.
The signal is multiplied by the locally generated carrier cosωct and then passed
through a low-pass filter.
(a) Prove that the modulating signal can be completely recovered if the cut-off
frequency of the filter is fN < fo < 2fc.
(b) Determine the recovered signal when the multiplying signal is cos[ωc + ].
(c) Determine the recovered signal when the multiplying signal is cos[(ωct+
ω)t].
Give
 << i where ωc = 2fc,
ω = 2Q
f. [16]
4. Explain demodulation of FM signal with the help of PLL. [16]
5. Compare noise performance of PM and FM system. [16]
6. (a) Draw the block diagram of an SSB - SC transmitter employing sideband sup-
pression filter and explain.
(b) Why are limiters and preemphasis filters used in FM radio. [16]
7. (a) Explain the working of TRF receiver with its block diagram.
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Code No: R05220405 Set No. 2
(b) A TRF receiver is turned to 1000 KHz AM radio broadcast signal by a variable
tuned circuit with 1 KHz bandwidth. Find the bandwidth when receiver is
returned to 1550 KHz and 550 KHz. Determined the recovered baseband. [16]
8. (a) Describe the generation and demodulation of PPM with the help of block
diagram and hence discuss its spectral characteristics.
(b) Define and distinguish between PTM and PAM schemes. Sketch and explain
their waveform for a single tone sinusoidal input signal. [16]
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Code No: R05220405 Set No. 3
II B.Tech II Semester Regular Examinations, Apr/May 2008
ANALOG COMMUNICATIONS
( Common to Electronics & Communication Engineering and Electronics &
Telematics)
Time: 3 hours Max Marks: 80
Answer any FIVE Questions
All Questions carry equal marks
⋆ ⋆ ⋆ ⋆ ⋆
1. (a) Draw the one cycle of AM wave and calculate the modulation index of it in
terms of Vmax and Vmin voltages.
(b) A modulating signal consists of a symmetrical triangular wave having zero dc
component and peak to peak voltage of 12V. It is used to amplitude modulate
a carrier of peak voltage 10V. Calculate the modulation index and the ratio
of the side lengths L1/L2 of the corresponding trapezoidal pattern.
(c) The rms antenna current of an AM transmitter is 10 A when un-modulated and
12 A when sinusoidally modulated. Calculate the modulation index. [6+6+4]
2. (a) Explain about the quadrature null effect of coherent detector.
(b) In DSB-SC, suppression of carrier so as to save transmitter power results in
receiver complexity - Justify this statement. [8+8]
3. (a) Why SSB transmission is the preferred than DSB-SC?
(b) i. Prove that the signal s(t) =
NP
i=1
cos [(ωct) cos (ωit + i) − sin (ωct) sin (ωit + i)]
is an SSB signal (fc >> fN), where ωc = 2fc, carrier angular frequency
and ωi = 2fi is modulating angular frequency. Identify the side band.
ii. Obtain an expression for missing side band.
iii. Obtain an expression of the total DSB-SC signal. [4+12]
4. (a) Describe generation of FM carrier by Transistor reactance modulator with
necessary diagrams.
(b) Compare the phasor diagram of narrow band FM signal and AM signal and
discuss about the similarities and differences of the two signals. [8+8]
5. (a) Derive the expression for figure of merit of AM system for large case.
(b) Given an analog base band communication system with additive white noise
having power spectral density 
2 and a distorting channel having the frequency
response. The distortion is equalized by a receiver filter having the frequency
response
Hc (w) = 1
1+Jw/w
Heq (w) =  1
Hc(w) 0  |w|  w
0 otherwise
Obtain an expression for the output SNR.
[16]
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Code No: R05220405 Set No. 3
6. (a) Classify radio transmitters based on the type of modulation and Service in-
volved.
(b) Explain AM transmitters with modulation at high carrier power level with the
help of its block diagram. [16]
7. (a) With the aid of the block diagram explain TRF receiver. Also explain the
basic superheterodyne principle.
(b) List out the advantages and disadvantages of TRF receiver. [16]
8. (a) How is PDM wave converted into PPM system.
(b) Explain why a single channel PPM of system requires the transmission of
synchronization signal, where as a single channel PAM or PDM system does
not it. [16]
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Code No: R05220405 Set No. 4
II B.Tech II Semester Regular Examinations, Apr/May 2008
ANALOG COMMUNICATIONS
( Common to Electronics & Communication Engineering and Electronics &
Telematics)
Time: 3 hours Max Marks: 80
Answer any FIVE Questions
All Questions carry equal marks
⋆ ⋆ ⋆ ⋆ ⋆
1. (a) Draw the one cycle of AM wave and calculate the modulation index of it in
terms of Vmax and Vmin voltages.
(b) A modulating signal consists of a symmetrical triangular wave having zero dc
component and peak to peak voltage of 12V. It is used to amplitude modulate
a carrier of peak voltage 10V. Calculate the modulation index and the ratio
of the side lengths L1/L2 of the corresponding trapezoidal pattern.
(c) The rms antenna current of an AM transmitter is 10 A when un-modulated and
12 A when sinusoidally modulated. Calculate the modulation index. [6+6+4]
2. (a) Explain the DSB-SC generation by balanced modulator using diodes.
(b) The modulating signal in an AM-SC system is a multiple-tone signal given by
m(t) = A1 cos ω1t + A2 cos ω2t + A3 cos ω3t. The signal m(t) modulates a
carrier Ac cos ωct. Plot the single-sided spectrum and find the bandwidth of
the modulated signal. Assume that ω3 > ω2 > ω1 and A1 > A2 > A3 . [8+8]
3. (a) Why VSB system is widely used for TV broadcasting - Explain?
(b) An AM transmitter of 1KW power is fully modulated. Calculate the power
transmitted if it is transmitted as SSB.
(c) Calculate the filter requirement to convert DSB signal to SSB Signal, given
that the two side bands are separated by 200HZ. The suppressed carrier is 29
MHZ. [6+4+6]
4. (a) Give the procedure to determine the effective bandwidth of an FM signal.
(b) Which method of FM signal generation is the preferred choice, when the sta-
bility of the carrier frequency is of major concern? Discuss about the method
in detail. [8+8]
5. (a) Find the output SNR in a PM system for tone modulation.
(b) A phase modulation (PM) system, with the modulated wave defined by S (t) =
Ac Cos [2π fct + kpm(t)]
where kp is a constant and m(t) is the message signal. The additive noise n(t)
at the phase detector input is
n(t) = nI(t) cos (2πfc t)−nQ (t) sin 2πfc t Assuming that the carrier-to-noise
ratio at the detector input is high compared with unity, determine
i. the output signal-to-noise ratio and
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Code No: R05220405 Set No. 4
ii. the figure of merit of the system. [16]
6. (a) Classify radio transmitters in detail.
(b) Compare low level modulation and high level modulation of radio transmitters.
[16]
7. (a) Describe the circuit of an FET amplitude limiter, and with the aid of the
transfer characteristic explain the operation of the circuit.
(b) What can be done to improve the overall limiting performance of an FM
receiver ? Explain the operation of the double limiter and also AGC in addition
to a limier. [16]
8. (a) What is the fundamental difference between pulse modulation, on the one
hand, and frequency and amplitude modulation on the other?
(b) What is pulse width modulation? What other names does it have? How is it
demodulated? [16]
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ANTENNAS AND WAVE PROPAGATION

Code No: R05310403 Set No. 1
III B.Tech I Semester Regular Examinations, November 2007
ANTENNAS AND WAVE PROPAGATION
( Common to Electronics & Communication Engineering and Electronics &
Telematics)
Time: 3 hours Max Marks: 80
Answer any FIVE Questions
All Questions carry equal marks
⋆ ⋆ ⋆ ⋆ ⋆
1. (a) Draw the Dual characteristics of an antenna.
(b) Explain the Radiation from Two wire. [8+8]
2. (a) Derive the expressions for electric field in case of short current element and
hence obtain the conditions for the field to be in Franhofer region.
(b) Find the distance from a radiating element with 60Hz current such that radi-
ation and induction fields are equal. [10+6]
3. (a) A linear broadside array consist of 4 identical equal in phase point source with
λ/3 spacing. Calculate and plot the field pattern. Also find the directivity
and beam width.
(b) What is optimum spacing used in parasitic array? Why. [12+4]
4. (a) Write short notes on “Helical Antenna”.
(b) Derive an expression for radiated electric field strength of a traveling wave
radiation of length ‘l’. [8+8]
5. (a) Sketch the current distribution of folded dipole and find out input impedance
when two legs have unequal diameters.
(b) A Parabolic dish provides a power gain of 50dB at 10GHz, with 70% efficiency.
Find out
i. HPBW.
ii. BWFN, diameter. [8+8]
6. (a) Describe the method of measuring the gain and radiation pattern of an an-
tenna.
(b) A standard gain horn antenna with a power gain of 12.5, is used to measure the
gain of a large directional antenna by comparison method. The test antenna
is connected to the receiver and an attenuator adjusted to 23dB in order to
have the same receiver output. Find out the gain of the large antenna. [8+8]
7. (a) Describe the following:
i. Space wave propagation.
ii. Duct propagation.
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Code No: R05310403 Set No. 1
(b) VHF communication is to be established with a 50watt transmitter at 100MHz.
Calculate the LOS distance if the heights of transmitting and receiving an-
tennas are respectively 50m and 10m. Assuming the capture area of the
transmitting antenna is 25sqmts, calculate the field strength at the receiving
neglecting ground reflected wave. [8+8]
8. (a) Discuss the characteristics of F1 and F2 layers.
(b) Discuss the reasons for reduction of field strength in sky wave propagation.
[8+8]
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Code No: R05310403 Set No. 2
III B.Tech I Semester Regular Examinations, November 2007
ANTENNAS AND WAVE PROPAGATION
( Common to Electronics & Communication Engineering and Electronics &
Telematics)
Time: 3 hours Max Marks: 80
Answer any FIVE Questions
All Questions carry equal marks
⋆ ⋆ ⋆ ⋆ ⋆
1. (a) Distinguish between Directive Gain and Power Gain.
(b) An antenna has a radiation resistance of 73 ohms and a lossy resistance of 7
ohms. If the power gain is 20, calculate the directivity and the efficiency of
the antenna. [8+8]
2. (a) Derive an expression for radiance resistance of current element starting from
the expression for radiation fields.
(b) Prove that the impedance of an isolated antenna when used for receiving is
same as when used for transmitting. [8+8]
3. (a) In order to scan the beam of a linear array to 300 off broadside. Calculate the
inner element phase shift required if the elements are spaced at 3 cms and the
frequency is 64 KHz.
(b) What are linear arrays. Compare Broadside array and End fire array. [8+8]
4. (a) Derive an expression for electric field of a Non Resonant antenna of length ‘l’
carrying current.
(b) Sketch and explain the constructional features of a Helical Antenna. [10+6]
5. (a) What is a Parasitic Element? Describe the use of different types of parasites
in TV receiving antennas.
(b) Derive an expression for aperture field distribution of a parabolidal reflector.
[8+8]
6. (a) Describe the method of measuring the gain and radiation pattern of an an-
tenna.
(b) A standard gain horn antenna with a power gain of 12.5, is used to measure the
gain of a large directional antenna by comparison method. The test antenna
is connected to the receiver and an attenuator adjusted to 23dB in order to
have the same receiver output. Find out the gain of the large antenna. [8+8]
7. (a) Define MUF and Critical frequency. Derive the expressions for the same.
What is Secant law?
(b) Describe the Ground wave propagation. [8+8]
8. (a) Derive the field strength of tropospheric wave.
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Code No: R05310403 Set No. 2
(b) Give an account of effect of earths imperfections and roughness. [8+8]
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Code No: R05310403 Set No. 3
III B.Tech I Semester Regular Examinations, November 2007
ANTENNAS AND WAVE PROPAGATION
( Common to Electronics & Communication Engineering and Electronics &
Telematics)
Time: 3 hours Max Marks: 80
Answer any FIVE Questions
All Questions carry equal marks
⋆ ⋆ ⋆ ⋆ ⋆
1. (a) Define the terms:
i. Beam Width
ii. Side Lobe Level
iii. Polarization
iv. Effective Aperture Area.
(b) What is the effective length of an antenna. Determine the effective length of
a half wave dipole antenna. [8+8]
2. (a) Show that the radiation resistance of a small loop is equal to 320π 4(A/λ2)
ohms where A is loop area.
(b) What is Folded Dipole ? Find its Radiation Resistance. [8+8]
3. (a) Explain the procedure for measuring the radiation pattern of a half wave
dipole.
(b) What is the requirement for tapering of arrays.
(c) State the applications of arrays. [8+4+4]
4. (a) State the advantages and disadvantages of Rhombic Antenna.
(b) Draw the radiation pattern for traveling wave antenna for L=λ/2,λ,2 λ,4λ and
8 λ. [8+8]
5. (a) What is a Parasitic Element? Describe the use of different types of parasites
in TV receiving antennas.
(b) Derive an expression for aperture field distribution of a parabolidal reflector.
[8+8]
6. (a) Describe the method of measuring the gain and radiation pattern of an an-
tenna.
(b) A standard gain horn antenna with a power gain of 12.5, is used to measure the
gain of a large directional antenna by comparison method. The test antenna
is connected to the receiver and an attenuator adjusted to 23dB in order to
have the same receiver output. Find out the gain of the large antenna. [8+8]
7. It is defined to establish short wave communication between two points on earths
surface(assumed flat) separated by 1200km. Calculate MUF and angle of take off
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Code No: R05310403 Set No. 3
of the transmitted wave from the following: Highest signal frequency returned to
earth after vertically upward propagation=7.2MHz. Virtual height of the ionized
layer=200kms. Deduce the working formula. [16]
8. (a) Distinguish between Radio and Optical horizons. Give the reasons.
(b) Write short notes on M-Curves. [8+8]
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Code No: R05310403 Set No. 4
III B.Tech I Semester Regular Examinations, November 2007
ANTENNAS AND WAVE PROPAGATION
( Common to Electronics & Communication Engineering and Electronics &
Telematics)
Time: 3 hours Max Marks: 80
Answer any FIVE Questions
All Questions carry equal marks
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1. (a) Define antenna beam width and directivity and obtain the relation between
them.
(b) Calculate the electric field (Erms) due to an isotropic radiator radiating 3KW
power at a distance of 2 Km from it. [8+8]
2. (a) State the following antenna theorems and bring out their importance in an-
tenna measurements :
i. Reciprocity theorem.
ii. Maximum power transfer theorem.
(b) A half wave transmitting antenna radiates 10KW of power at 100MHz.If the
heights of transmitting and receiving antennas are 100m and 9m, calculate the
power received at a distance of 10kms from the transmitting antenna. [8+8]
3. (a) Calculate
i. HPBW
ii. Solid Angle if a linear array having 10 isotropic point source with λ/2
spacing and phase difference δ=900.
(b) Write short notes on Hansen-Wood yard end fire array. [8+8]
4. (a) Distinguish between Traveling wave and Standing wave antennas.
(b) Compare Resonant and Non Resonant antennas.
(c) Explain the working of Rhombic antenna. [4+4+8]
5. (a) Compute the gain, principle beam width and HPBW of a 10m diameter par-
abolic dish with a half wave length dipole feed in focus at 10GHz.
(b) Explain the Cassegrain mechanism in transmission mode. List out the advan-
tages and disadvantages of Cassegrain feed. [8+8]
6. (a) What is an electromagnetic horn antenna? What are its applications? The
length of an E-plane sectoral horn is 15cms. Design the horn dimensions such
that it is optimum at 10GHz.
(b) Calculate the minimum distance required to measure the field pattern of an
antenna of diameter 2m at a frequency of 3GHz. Derive the necessary equa-
tion. [8+8]
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Code No: R05310403 Set No. 4
7. (a) Show that Ionosphere act as a variable refractive index medium.
(b) A radio link has to be established between two earth station at a distance of
25000kms. If the height of ionosphere is 200kms and its critical frequency is
5MHz. Calculate the MUF for the given path. Also calculate the electron
density in the ionosphere layer. [8+8]
8. (a) Describe the troposphere and explain how tropospheric ducts can be used for
microwave propagation.
(b) Derive the expression for space wave electric field produced by an antenna at
a distance point, assuming a flat earth. [8+8]
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