15EC71-MICROWAVES AND ANTENNAS - Question Bank
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1. Starting from the fundamentals,
derive expressions for voltage and current at any point on the transmission line. (10
M)
2. The characteristic impedance of a certain line is
710 -16°, when the frequency is 1 KHz. At this frequency, the attenuation is
0.01 neper/km and the phase function is 0.035 radians/km. calculate the
resistance, the leakage inductance, the capacitance per km and the velocity of
propagation. (10 M)
3. Derive the relationship between reflection
coefficient and standing wave ratio. ( 05 M)
4. The load
impedance of ZL =(60-j80)Ω is required to be matched to a 50 Ω
coaxial line by using a short Circuited stub of length ‘l’ located at a
distance ‘d’ from the load. The wavelength
of operation is 1m. Using smith chart, find ‘d and ‘l’. (10 M)
5.Derive
expressions for the length of the stub and the distance of stub from the load
for single stub impedance. (10 M)
6. Derive the
equations for the following with respect to a transmission line:
a. Propagation constant b. attenuation constant c. phase constant
d.
characteristic impedance (10 M)
7. What are the applications of smith chart?
Explain briefly. ( 05 M) 8. A transmission line has the
following primary constants per km of the line: R = 8 Ω, G =
0.1 µmho, L = 3.5 mH, and C = 9nF.
Calculate Z0, α, β, Vp and λ at ω = 5000 rad/sec. (06 M) 9. What are standing waves and
standing wave ratio? (04 M) 10. Explain in brief single stub matching.
State the important expressions related to it.
(05
M) 11. The characteristic impedance
of a line is 50 Ω and SWR =2 when the line is loaded. When the line is shorted,
the minima shifts 0.15 λ towards the load. Determine the load impedance. Use
smith chart. (05
M) .
12. Derive an
expression for the reflection coefficient and transmission coefficient in the
transmission line. (08M)
13. A telephone
line has R = 6 ohms/km, L = 2.2 mH/km, C = 0.005 µF/km and G = 0.05 µmhos/km.
Determine Zo, α, β and phase velocity at 1KHz. (06
M)
14. Derive an
expression for the line impedance of transmission line in terms of Zs and Zo. (05
M)
15. A load
impedance of ZR = 60 – j 80Ω is required to be matched to a 50 ohm co-axial
line, by using a short circuited stub of length ‘l’ located at a distance ‘d’
from the load. The wavelength of operation is 1 meter. Using smith chart, find
‘d’, ‘l’. (07 M)
16. A load
impedance of 26 – j 16 Ω is required to be connected to a line of
characteristic impedance 100 Ω by using a short circuited stub of length l
located at a distance, d from the load. The wavelength of operation is 1 m.
Using smith chart find d and l. write the procedural steps. (10 M)
17. The
normalized impedance of a microwave transmission line Zl = 1 + j1 and the
operating wavelength λ = 5 cm. Using smith chart determine the first voltage
maxima, first voltage minima from the load. Also find VSWR. (09 M)
18. A generator
of 1 volt, 1 KHz supplies power to 100 Km long line terminated Zo. The
parameters of the line are R = 10.4 Ω/km, L = 0.00367 H/km, G = 0.8* 10 -6
mhos/km and C = 0.00835 * 10-6 F/km. calculate Zo, attenuation
constant and phase constant. (06 M)
19. With the
help of neat diagrams, explain the working of "Reflex Klystron"
oscillator. (08
M)
20. A dc beam
voltage of 280 volts is applied to the anode of a reflex klystron whose cavity
is tuned to a frequency of 9.75 GHz. The length of the repeller space is 1.2 *
10-3m and is operated under 2 3/4 mode of operation. If the
resulting beam current is 1.5 mA, determine the optimum power value of RF power
and the corresponding repeller voltage to be applied. (06
M)
21. Bring out
the meaning of electronic admittance of reflex klystron and obtain an
expression for the same.
(10
M)
22. Draw and
explain the mode curves of Reflex Klystron. (05 M)
23. A
transmission line has a characteristic impedance of 50 + j0.01 Ω and terminated
in a load impedance of 73 - j42.5 Ω. calculate i) reflection coefficient
ii)SWR Dec 2018/Jan 2019 (04 M)
24. Define
reflection coefficient. Derive the equation for reflection coefficient at the
load end at a distance 'd' from the load.
Dec 2018/Jan 2019 (06 M)
25. Describe the
mechanism of oscillation of reflex klystron. Dec 2018/Jan 2019 (06 M)
26. A
transmission line has the following parameters: R = 2 Ω/m, G = 0.5mmho/m, f = 1
GHz, L = 8 nH/m, C = 0.23 pF/m. calculate : i) characteristic impedance ii)
propagation constant
Dec 2018/Jan 2019 (04 M)
MODULE
2
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1.
State and prove the properties of
S-parameters. (10 M)
2.Derive the
S-matrix of a two port network with mismatched load. (06
M)
3.Show that the
Z & Y matrices are symmetric for a reciprocal network. (04
M)
4.Two transmission lines of characteristic impedance
Z1 and Z2 are joined at the plane PP’. Express the s-parameters in terms of
impedances. Dec 2018/Jan 2019 (06 M)
5.Explain
S-Matrix representation of multiport network.
(04
M)
6.Explain the
relation between incident and reflected waves in terms of scattering parameters
for a two port network. Also explain physical significance of s-parameters. (08
M )
7.Which
properties are common in S, Z and Y matrices?
(03 M)
8.Write the
relationship of ABCD parameters with z parameters. (04 M)
9.Define
insertion loss, transmission loss, return loss interms of s-parameters. (10
M)
10. Explain the properties of magic tee. Obtain the
S-matrix representation of magic tee.
(10 M)
11.Explain with a neat sketch, a precision rotary
phase shifter. Derive expression for the output field component Eo in terms of
the incident field Ei. (10 M)
12.
Explain with neat sketches different coaxial connectors used for microwave
applications.
(07 M)
13. A 20 mw signal is fed into one collinear port 1 of a lossless
H-plane T-junction. Calculate the power delivered through each port when other
ports are terminated in matched load. Dec 2018/Jan 2019 (03 M)
14.With a neat diagram, explain the
operation of microwave attenuator. (06 M)
15.
With a neat diagram, explain the working
of a H-plane Tee junction. Also derive its scattering matrix. (10
M)
16.
With a neat diagram, explain the working of a E-plane Tee junction. Also derive
its scattering matrix. (10
M) 17. With neat diagram, explain the
working of precision type variable attenuator.
Dec 2018/Jan 2019 (06 M)
18. What is
magic tee? Derive its scattering matrix. Dec 2018/Jan
2019 (06 M)
19. Discuss
different types of coaxial connectors. Dec
2018/Jan 2019 (04 M)
MODULE 3
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1. A copper strip line conductor has
dimensions w = 0.112 cm and b = 0.28 cm. Determine the characteristic impedance
of the strip line assuming negligible thickness if the dielectric constant of
the substrate is εr= 3.16. (06 M)
2.
A microstrip line is composed of negligible thickness copper conductor mounted
on a dielectric substrate of thickness 1.4 mm, loss tangent of 4 * 10-4
and dielectric constant of 9.6. The width of the microstrip line is 3 mm and is
operated at 10 GHz frequency. Determine (i) characteristic impedance Zo (ii)
Effective dielectric constant (iii) Attenuation due to conductor loss and
dielectric loss (iv) radiation factoR. (10
M)
3.
With neat diagram, explain the operation of parallel strip lines. Write the
expressions for the distributed parameters, Characteristic impedance and the
attenuation in parallel strip
(10 M)
4.
With neat diagrams, and expressions explain the various losses in microstrip
lines. (10 M)
5.
Compare strip line and microstrip line.
(06 M)
6.
with a neat sketch explain the different types of strip lines. (08 M)
7.
A lossless parallel strip line has a conducting strip width W. The substrate
dielectric separating the two conducting strips has a relative dielectric
constant of 6 and a thickness d of 4 mm. Evaluate w, C and vp (in usual
notations) (08 M)
8.
with a neat diagram, explain the operation of parallel strip line. Write the
expression for distributed parameters, characteristic impedance and attenuation
losses. (10 M)
9.
Explain the construction and field patterns for microstrip line. (08
M)
10.
A shielded strip line has dielectric constant of the insulator = 2.56, strip
width W = 25 mils, strip thickness t = 14 mils, shield depth d = 70 mils,
calculate i) K factor ii)the fringe
capacitance iii) the characteristic
impedance of the line. (06
M)
11.
Calculate the characteristic impedance of a wide microstrip line having
negligible thickness and having a width at 0.8 mm, thickness at substrate 0.2
mm and has a dielectric constant 3.55 (04 M)
12.
Determine
the directivity of the system if the radiation intensity (i)U=Um
sinθ sin2φ and(ii)U= Um cosφ sin2θ.
(10 M)
13.
Define the terms directivity and effective
aperture of an antenna. Derive a relation for directivity in terms of effective
aperture. (06 M)
14.
Prove that the directivity for a source
with a unidirectional power pattern is given by U=Umcosnθ
can be expressed as Dn =2(n+1). U has a value for 0≤θ≤π/2 and
0≤φ≤2π. (04
M)
15.
An antenna has a field pattern given by E(θ) = cosθ cos2θ for 0≤θ≤90°. Find the
Half power Beam width and the Beam width between First nulls.
(05 M)
16.
Calculate the maximum power received at a distance of 0.5 Km over a free space
1 GHz circuit consisting of a transmitting antenna with 25 dB gain and a
receiving antenna of gain 20 dB. Assume the transmitting antenna input is 150
Watts. (05 M)
17.
Derive
an expression for effective aperture and directivity of (i) a linear λ/2
dipole (ii)a short antenna dipole. (10 M)
18.
Define the
following with respect to an antenna:
a. Radiation pattern b. Beam area
c. Effective aperture d. Effective
height (10 M)
19. A radio link has 15 W transmitter
connected to an antenna of 2.5 m2 effective aperture at 5 GHz. The
receiving antenna has an effective aperture of 0.5 m2 and is located
at a 15 Km line of sight distance from the transmitting antenna. Assume
lossless antennas. Find the power delivered to the receiver. (05 M)
20.Find the directivity of a source with
unidirectional cosine squared power pattern. (05 M)
21. The
radiation intensity of an antenna is given by U = cos4θ sin2θ
for 0≤θ≤π/2 (05
M)
22. Prove that the directivity for a source with
a unidirectional power pattern is given by U=Umcosnθ can
be expressed as Dn =2(n+1). U has a value for 0≤θ≤π/2 and
0≤φ≤2π.
(05 M)
23. Define
the following terms with respect to antenna: i) Gain ii)Isotropic radiator iii)
Beam area iv)Radiation resistance
(08
M)
24. The
effective apertures of transmitting and receiving antennas in a communication
system are 8λ2 and 12λ2 respectively, with a separation
of 1.5 km between them. The e.m wave is travelling with a frequency of 6 MHz
and the total input power is 25 KW. Find the power received by the receiving
antenna. Dec 2018/Jan 2019 (04 M)
25.
Calculate the maximum power received at a distance of 0.5 Km over a free space
1GHz circuit consisting of transmitting antenna with 25 dB gain and a receiving
antenna gain of 20 dB. Assume the transmitting antenna input is 150 Watts. (06 M)
26. Explain
the construction and field pattern for microstrip line. Dec 2018/Jan 2019
(06 M)
27. Explain the following terms as
related to antenna system:i) directivity
ii)beam efficiency
iii)effective aperture.
Dec 2018/Jan 2019 (06 M)
28. Explain coplanar strip lines and
shielded strip lines. Dec 2018/Jan 2019 (06 M)
29. Write a
note on antenna field zones.
Dec 2018/Jan 2019 (06 M)
.
MODULE 4
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1. Derive expressions for the
maxima, null directions, directions of side lobes, HPBW and FNBW for N
isotropic point sources with equal amplitude and opposite phase. (10 M)
2. Obtain the field pattern for a
linear uniform array of 6 isotropic point sources spaced λ/2 distance apart.
The power is applied with equal amplitude and in phase. Also find HPBW and
FNBW.
(08
M)
3. Derive
an expression for power radiated from an isotropic source with sine squared
power pattern. Also find the directivity D and draw the power pattern. (06 M)
4. Show that the effective height and effective
aperture are related via the radiation resistance and the intrinsic impedance
of free space.
(04 M)
5. State
and explain power theorem and its application to an isotropic source. (05
M)
6. 4 isotropic sources are placed λ/6 m apart.
They have a phase difference of π/3
between the adjacent elements. Find the beam width between first
nulls. (05 M)
7. Derive an expression for field
intensity for two isotropic point sources with equal amplitude and equal
phase.
(10 M)
8. Eight point sources are placed
λ/6 apart. They have a phase difference of π/3
between adjacent elements. Obtain the field pattern. Also find BWFN and HPBW. (08 M)
9. Find the beam area of the electric
field intensity pattern given by the expression
En = sinθ, 0≤θ≤π. (05 M)
10. Show that the radiation resistance of a half wave
dipole antenna is 73 Ω. .
Dec
2018/Jan 2019 (06
M)
11. Starting from electric and magnetic potentials,
obtain the far field components for a short dipole.
(12 M)
12. Derive an expression for radiation resistance of a
short electric dipole (08 M)
13. For a broadside array of n isotropic point source
of equal amplitude and spacing, show that φ0 = cos-1 (±kλ/nd),
where φ0 gives the null directions. Find the null directions for an
array of 4 isotropic point sources with λ/2 spacing. (06
M)
14. Obtain the field pattern for a dipole of length
i)λ/2 ii)3λ/2 (06 M)
15. Obtain the expression for the instantaneous
electric field and magnetic field at a large distance r from a loop of any
radius a.
(08 M)
16. Distinguish between end fire array and broad side
array. (06 M)
17. Explain the principle of pattern multiplication
with an example. Dec
2018/Jan 2019 (06 M)
18. A
source has a radiation intensity power pattern given by U = Um sin2θ
for 0 ≤ θ ≤ π
; 0 ≤ φ ≤ 2π. Find the total power and directivity.
Draw pattern. . Dec 2018/Jan 2019 (04 M)
19. A
source has a cosine radiation intensity power pattern given by U = Um cos θ for
0 ≤ θ ≤ π/2 ;
0 ≤ φ ≤
2π. Find the total power and directivity. Dec 2018/Jan 2019 (04 M)
MODULE 5
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1. With a neat figure, explain the working of Yagi-Uda
antenna.Mention the design formulae used
for various elements. Mention its applications.
(10 M)
2. With neat diagrams, explain the construction of log
periodic dipole array, and explain the different regions of operation.
(10 M)
3. Determine the length 'ρ' of the horn, the H-plane
aperture and flare angle θH & θE of a pyramidal horn
for which the E-plane aperture is 10λ. The horn is fed with a rectangular
waveguide with TE10 mode. Let D = 0.2 λ in the E-plane and 0.35 λ in
the H-plane. Also calculate the beamwidth and directivity.
(10 M)
4. Design a Yagi-Uda antenna of 6 elements to provide
a gain of 12 dB if the operating frequency is 200 MHz.
(05 M)
5. Differentiate between corner reflector and
parabolic reflector antennas.
(05 M)
6. For what mouth diameter and capture area of a
parabolic system is BWFN of 12° is
obtained when it is operated at 2.5 GHz.
(05
M)
7. Explain the practical design considerations of
helical antenna. What are the two modes of operation of helical antenna. (10
M)
8. Discuss the features of a loop antenna. Derive an
expression for the far field components of a loop antenna.
(10
M)
9. Determine: i) The length L, aperture aH
and half angles in E and H planes for a pyramidal horn antenna, for whcih aE
= 10 λ. The horn is fed with a rectangular wave guide in TE10 mode.
Let δ = λ/12 in the E-plane and δ = λ/6 in the H-plane. ii) Calculate the
directivity D. Also determine the beam width Dec
2018/Jan 2019 (05 M)
10. The radius of a circular loop antenna is 0.02 λ.
How many turns of the antenna will give a radiation resistance of 35Ω.
(05
M)
11. Explain the following design parameters of a
helical antenna: i) Beam width ii) Axial
ratio iii) Impedance.
(06
M)
12. Show that the radiation resistance of loop antenna
is given by 31200(nA/λ2 )2 (08 M)
13. Explain the working and design considerations of
Log-Periodic antenna. Dec 2018/Jan 2019 (06 M)
14.
A 16 turn helical beam antenna has a circumference of λ and turn spacing of
λ/4. Find i) HPBW ii) axial ratio iii) directivity .
Dec
2018/Jan 2019 (04 M)
15.
Write short notes on : i)Yagi Uda array ii)Parabolic reflector Dec 2018/Jan 2019 (04 M)
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