# SAMPLE PAPER OF MICROWAVE ENGINEERING

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SAMPLE PAPER OF MICROWAVE ENGINEERING

SAMPLE PAPER OF MICROWAVE ENGINEERING

SHORT QUESTIONS(All Questions are compulsory)

1. Define s-matrix .
ans : In a microwave junction there is intersection of three or more components.There will be an
output port ,in addition there may be reflection from the junction of other ports.Totally there may be  many combinations,these are represented easily using a matrix called S matrix.
2. What are the .Properties of s-matrix?
ans : 1.It possess symmetric property  2.It possess unitary property [s][s]*=[i]
3. What is transmission matrix?
ans: When a number of microwave devices are connected in cascade.Each junction is represented by a transmission matrix which gives the output quantities in terms of input quantities.
4. State the unique property of Scattering matrix?
ans: Unitary Property: the row of a scattering matrix multiplied by the complex conjugate of the same row of the scattering matrix is one.
5. Define VSWR
ans:  Voltage standing wave ratio is defined as the ratio of maximum voltage to the minimum
voltage VSWR=Vmax/Vmin.
6. What are hybrid couplers?
ans: Hybrid couplers are interdigitated microstrip couplers consisting of four parallel striplines
with alternate lines tied together,It has four ports.This type of coupler is called Lange hybrid
coupler.
7. Why isolators are called uniline?
ans: An ideal isolator completely absorbs the power for propagation in one direction and
provides lossless transmission in the opposite direction. Thus isolators are called uniline.
8. How are spurious oscillations generated in TWT amplifier? State the method to suppress it.
ans: In a TWT, adjacent turns of the helix are so close to each other and hence oscillations are
likely to occur. To prevent these spurious signals some form of attenuator is placed near the input end of the tube which absorb the oscillations.
9. State the applications of magnetrons. why magnetron is called as cross filed
device?
ans: 1) Pulse work in radar
2) Linear particle accelerators.
In cavity magnetron, there exists a radial electric field and an axial magnetic field perpendicular to each other and hence magnetron is called as a cross filed device.
10. What is frequency pulling and frequency pushing in magnetrons?
ans: Frequency pulling is caused by changes in the load impedance reflected into the cavity
resonators. Frequency pushing is due to the change in anode voltage which alters the orbital
velocity of electron clouds.
Radiation efficiency is defined as the ratio of total power radiated to total power accepted at its
input .
12. How do you measure the polarization?

ANS: The polarization of an antenna is measured using transmitting mode and probing the polarization  by a dipole antenna in the which the dipole is rotated in the plane of polarization and the received voltage pattern is recorded.

13. What is spectrum analyzer?

ANS: .ANS: Spectrum analyzer is a broad band super heterodyne receiver which is used to display a wave in frequency domain additionally, power measurements, side bands can also be observed.

14. List the methods for measuring dielectric constants?

ANS: 1.Waveguide method
2.cavity pertubaration method
ANS: Radiation pattern is a representation of radiation characteristics of an antenna which is a function of elevation angle azimuth angle for a constant radial distance and frequency.
.
ANS: Radiation efficiency is defined as the ratio of total power radiated to total power accepted at its input
.
17. How do you measure the polarization?
ANS: The polarization of an antenna is measured using transmitting mode and probing the polarization by a dipole antenna in the which the dipole is rotated in the plane of polarization and the received voltage pattern is recorded.

18. List some application of spectrum analyzer.

ANSl: 1. Identifying frequency terms and their power levels
2. Measuring harmonic distortion in a wave
3.Determine type of wave modulation
4. Signal to noise ratio
5. For identifying wave distortion

19. What is Transferred electron effect?

ANS: Some materials like GaAs exhibit negative differential mobility,when biased above a
threshold value of the electric field.This behaviour is called transferred electron effect.
20..What are time parameter for TED’S
ANS: a)Domain growth time constant
b)Dielectric relaxation time
c)transit time.