DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING
EC432 MICROWAVE ENGINEERING
TWO MARK QUESTIONS AND ANSWERS
1. Define s-matrix
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.
2What are the .Properties of s-matrix?
1.It possess symmetric property sij =sji
2.It possess unitary property
[s][s]*=[i]
3.Why is s-matrix used in MW analysis?
S matrix is used in MW analysis to overcome the problems which occurs when
H,Y,&Z parameters are used in high frequencies.
1.Equipment is not readily available to measure total voltage &total current at
the ports of the network.
2.Short and open circuits are difficult to achieve over a broad band of
frequencies.
3.Active devices,such as power transistor &tunnel diodes,frequently won’t
have stability for a short or open circuit.
4.Give ABCD matrix for a two port network
V1=A B V2
I1 C D -I2
5.What is ABCD matrix?
ABCD matrix is a transmission matrix.these parameters express voltage and
current at output in terms of those at input port.
V1=AV2-BI2
I1=CV2-DI2
6.What are the advantages of ABCD matrix?
1.They are used in power transmission lines.
2.They are very helpful in the case of cascade networks.
7.What is the Scattering matrix for N port device?
[S]= S11 S12 S13…… S1n
S21 S22 …………S2n
S31 S32 ………….S3n
. .
. .
. .
Sm1 Sm2 ………...Smm
8.Give the S matrix of uniform transmission line
S= 0 e-jbl
e-jbl 0
9.Give the properties of impedence [x]&admittance[y] matrix?
1.For a lossless junctionary y and z are symmetric .
2.[y]=[z] -1
3.Elements of matix [Z] &matrix [Y] are Frequency dependent.
10.For a loss less junction all the elements in the impedence &admittance matrices
are
Pure imaginary
11.What are the properties of scattering matrix for a lossless junctoion?
1.The product of any column of the S-matrix with conjugate of this column
equals unity.
2.The product of any column of the scattering matrix with the complex
conjugate of any
other column is zero.
12.What is transmission matrix?
When a number of microwave devices are connected in cascade.Each
junction is represented by a transmission matrix which gives the output quantities
interms of input quantities.
13.Define one port circuit.Give two examples.
A one port circuit is a circuit for which power can enter or leave through a
single wave
Guide or transmission line.
Examples:
1.Short-circuited co-axial line
14.Write the voltage matrix for an N-port microwave circuits.
V1 Z11 Z12 ….. Z1N I1
V2 Z12 Z22 …… Z2N I2
. = . . …… …. .
.
VN ZN1 ZN2 . ZNN IN
Where Zij=Elements of impedence matrix.
[Z]=Impedence martrix
15.For reciprocal media,the impedence and admittance matrices are
Symmetrical
16.For non-reciprocal media,the impedence and admittance matrices are
Ans: Asymmetrical
17.Give two examples for two port junctions.
1.The junction of two rectangular guides o ferrite devices?
Isolator Circulator Phaseshifters, Modulators, Power limiters
24. List two microwave devices using faraday rotation principles
Isolator, Circulator
25.What are powere dividers?
Power dividers are used to divide the input power into a number of smaller
amounts of power for exciting the radiating elements in an array antenna
26.What is the S-matrix of 3 port circulators?
Anticlockwise [S]= 0 1 0
0 0 1
1 0 0
Clockwise [S]= 0 0 1
1 0 0
0 1 0
27. Give the differences between Isolator and Circulator
28.What is
the S-matrix for 4
port circulators?
Clockwise
[S]= 0 0 0 1
1 0 0 0
0 1 0 0
0 0 1 0
Anticlockwise
[S] = 0 1 0 0
0 0 1 0
0 0 0 1
0 0 1 0
29.Give the S-matrix of E-plane Tee.
[S] = 0.5 0.5 0.707
0.5 0.5 -0.707
0.5 -0.707 0
30.Give the S-matrix of H-plane Tee
[S] = 0.5 -0.5 0.707
-0.5 0.5 0.707
0.707 0.707 0
31.Give the S-matrix of Magic Tee
[S] = 0 0 0.707 0.707
0 0 0.707 -0.707
0.707 0.707 0 0
0.707 -0.707 0 0
32.Give the Smatrix of directional coupler
[S] = 0 P 0 jq
P 0 jq 0
0 jq 0 P
Jq 0 P 0
Si.no Isolator Circulator
1 It is a 2 port device It is a 3 port device
2 It cannot be used as
circulator
It is used as isolator by
terminating one port
3 If input is given in port
1,output is obtained at
port 2 and vice versa
Each terminal is connected only
to the next terminal
33.Give an example for a two port MW device
Isolator is an example for a 2 port MW device
34.Give the applications of directional coupler
1.Unidirectional power measurement
2.SWR measurement
3.Unidirectional wave launching
4.Reflectometer
5.Balanced duplexer
35.What is Faraday’s rotation law?
If a circulary polarised wave is made to pass through a ferrite rod which has
been influenced by an axial magnetic field B ,then the axis of polarization gets tilted in
clockwise direction and amount of tilt depends upon the strength of magnetic field and
geometry of the ferrite.
36.Define VSWR
Voltage standing wave ratio is defined as the ratio of maximum voltage to the
minimum vottage
VSWR=Vmax/Vmin
37.What is Gyrator?
Gyrator is a two port device which provides a relative phase shift of 180 degree
for transmission from port 1 to port 2 as compared to the phase for transmission from
Port2 to port 1.
38.What is the principle of Microwave phase shifter?
When a wave propagates on a line,a phase difference prevails between any two
arbitary points along its paths.The phase difference between two points,
39.what are junctions?Give some examples
A microwave circuit consists of several microwave devices connected in some
way to achieve the desired transmission of MW signal.The interconnection of two or
more microwave may be regarded as MW junction.
Eg:Magic Tee,Hybrid Ring
40.What is Tee junction?Give two examples
In MW circuits a wave guide or coaxial junction with three independent ports is
referred to as tee junction.
Eg: E- Plane Tee,H-plane Tee
41.What is the other name for magic TEE?
Hybrid Tee
42.What is hybrid ring?
Hybrid ring consists of an annular line of proper electrical length to sustain
standing waves,to which four arms are connected at proper intervals by means of series
or parallel junctions.
43.What is the other name for Hybrid ring?
Rat-race circuit.
44.Name some wave guide components used to change the direction of the guide
through an arbitrary angle
Wave guide corner,Bend and twist
45.What are the different types of Directional coupler?
1.Two hole directional coupler
2.Be the hole directional coupler
3.Four hole directional coupler
46.What are hybrid couplers?
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.
47. What are nonreciprocal devices? Give two examples
The devices which are having the property that the forward characteristics are not
equal to the reverse characteristics are called non reciprocal devices.
48.Why isolators are called uniline?
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
49. Give some coupling parameters of directional coupler?
Coupling coefficient, Directivity, Insertion loss, Isolation
50. What are the high frequency effects in conventional tubes?
The high frequency effects in conventional tubes are
i) Circuit reactance
a)Inter electrode capacitance
b) Lead inductance
ii) Transit time effect
iii) Cathode emission
iv) Plate heat dissipation area
v) Power loss due to skin effect, radiation and dielectric loss.
51. What are the assumptions for calculation of RF power in Reflex Klystron?
i) Cavity grids and repeller are plane parallel and very large in extent.
ii) No RF field is excited in repeller space
iii) Electrons are not intercepted by the cavity anode grid.
iv) No debunching takes place in repeller space.
v) The cavity RF gap voltage amplitude V, is small compared to the dc beam
voltage VO
52. What is the condition for oscillation in Reflex klystron ?
The necessary condition for oscillation is that the magnitude of the negative real
part of the electronic admittance should not be less than the total conductance of the
cavity circuit i.e. -Ge G.
Where 1
G=Gc + Gb +G1 = ------
Rsh
Rsh effective shunt resistance
Gc copper losses of cavity
Gb beam loading conductance
G1 load conductance
53. Give the drawbacks of klystron amplifiers.
1. As the oscillator frequency changes then resonator frequency also changes
and the feedback path phase shift must be readjusted for a positive feedback.
2. The multicavity klystron amplifiers suffer from the noise caused because
bunching is never complete and electrons arrive at random at catcher cavity. Hence it is
not used in receivers.
54. What is the effect of transit time?
There are two effects.
1) At low frequencies, the grid and anode signals are no longer 180O out of
phase, thus causing design problems with feedback in oscillators.
2) The grid begins to take power from the driving source and the power is
absorbed even when the grid is negatively biased.
55. What are the applications of reflex klystron ?
1) Signal source in MW generator
2) Local oscillators in receivers
3) It is used in FM oscillator in low power MW links.
4) In parametric amplifier as pump source.
56. What is the purpose of slow wave structures used in TWT amplifiers?
Slow wave structures are special circuits that are used in microwave tubes to
reduce wave velocity in a certain direction so that the electron beam and the signal wave
can interact. In TWT, since the beam can be accelerated only to velocities that are about
a fraction of the velocity of light, slow wave structures are used.
57. How are spurious oscillations generated in TWT amplifier? State the method to
suppress it.
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.
58. State the applications of TWT.
1) Low power, low noise TWT’s used in radar and microwave receivers
2) Laboratory instruments
3) Drivers for more powerful tubes
4) Medium and high power CWTWT’S are used for communication and
radar.
59.How the klystron amplifier can act as klystron oscillator? What are the
applications of klystron amplifier?
When the klystron amplifier is given a positive feedback such that the overall
phase shift becomes zero 360° and Av = I then klystron amplifier acts as an
oscillator.
Applications:
(1) UHF TV Transmitters
(2) Long ranger radar
(3) Linear particle accelerator
(4) Troposcatter links
(5) Earth station transmitter.
60.Define phase focusing effect.
The bunching of electrons in known as “ Phase focusing effect”
This effect is important because without it, favoured electrons will fall behind the
phase change of electric field across the gaps. Such electrons are retarded at each
interaction with the R.F field in magnetron.
61.What do you mean by O-type tubes? Name some O-type tubes.
In O – type tube a magnetic field whose axis coincides with that electron
beam is used to hold the beam together as it travels the length of the tube. It is
also called as linear beam tube.
i) Helix Traveling wave tube
ii) Coupled cavity TWT
iii) Forward wave amplifier
iv) Backward wave amplifier
v) Backward wave oscillator
62. Define Transit time in Reflex klystron.
The time taken by the electron to travel into the repeller space and back to
the gap.
T =n + ¾
63. Write the parameters on which bunching depend on?
vi) Drift space should be properly adjusted.
vii) D.C anode voltage
viii) Signal amplitude should be such that proper bunching takes place.
64. Compare TWTA Klystron amplifier
Klystron amplifier TWTA
1. Linear beam or ‘O’ type device. Linear beam or ‘O’ type device
2. Uses cavities for input and Use non resonant wave circuit.
Output circuits.
3. Narrow band device due to Wide band device because use of use of
resonant cavities. Non-resonant wave circuit.
65. Give the performance Specification of Reflex klystron?
Frequency range: 2- 200 GHz
Band width: + 30 MHz for VR = + 10 V
Power output: 10 mw – 2.5W
Efficiency: 20 to 30%
66. What is CFA? State the applications of CFA.
CFA Cross Field Amplifier
CFA is a microwave power amplifier. It is a cross between TWT and
magnetron in its operation. i.e., it has a magnetron structure to provide an interaction
between crossed dc electric and magnetic fields on one hand and an RF field on the
other hand. It also uses a slow wave structure as in TWT to provide a continuous
interaction between the electron beam and a moving RF field.
Applications:
(1) Radar system
(2) Electronic counter measure.
67. State the characteristics of magnetron and of 2-cavity klystron amplifier.
Magnetron:
Operating frequencies 70 GH z
Output power 40 MW
Efficiency 40 to 70%
2-cavity klystron:
Efficiency 40%
Power output average power > 500 KW
Pulsed power > 30 MW
Power gain about 30 db.
68. What are the advantages of TWT?
1. Bandwidth is large.
2. High reliability
3. High gain
4. Constant Performance in space
5. Higher duty cycle.
69. What is meant by strapping?
The magnetron has eight or more coupled cavity resonators and hence
several modes of oscillation are possible. The oscillating frequency of
different modes are not same and are quite close to each other which
results in mode jumping. i.e., a 3 cm mode oscillation which is normal
for a particular magnetron
3
Could become a 3.05 cm------- mode oscillation. This result in
4
oscillations of reduced power at wrong frequency. To prevent this.
Strapping is used. It consists of two rings of heavy gauge wire connecting alternate
anode poles. It provides a phase difference 0f 2 radians for the modes other -mode
and thus preventing the occurrence of other modes, except the -mode .
70. State the applications of magnetrons. why magnetron is called as cross filed
device?
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.
71. What is BWO? State the applications of BWO.
A backward wave oscillator (BWO) is microwave cw oscillator with an
enormous tuning and ever all frequency coverage range.
Applications:
(i) It can be used as signal source in instruments and transmitters.
(ii) It can be used as broad band noise sources which used to confuse
enemy radar.
72. What is hull cutoff condition?
In a magnetron, the electron will just graze the anode and return towards
the cathode depends on Vo and Bo . The hull cut of magnetic equation is
Boc = (8Vo m / e) ½
-------------
b(1- a 2 / b2 )
The hull cutoff voltage equation is
Voc = e BO2 b2 (1- a2/ b2 )
…….
8m
If B0>BOe for given Vo.the electrons will not reach anode.
If Vo < Voc for a given Bo the electrons will not reach the anode.
73. What are the principal limitations of conventional negative grid electron tubes?
1) Electron transit time becomes a noticeable proportion at high frequencies.
2) Lumped electrical reactance and low Q resonant circuit.
74. What is frequency pulling and frequency pushing in magnetrons?
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.
75.What are the applications of High Q-oscillators and amplifier circuits?
They are used in
a)Low power transmitters
b)Parametric amplifier pumps
c)Police radars and intrusion alarms.
76.What are the Key phenomenon taking place in TRAPATT diode?
The Key phenomena are
a)Carrier generation by impact ionization producing a current pulse of phase
delay of 90 degree.
b)An additional phase shift introduced by the drift of carriers.
77.What is the operating frequency of TRAPATT devices?
TRAPATT devices operate at frequencies from 400 MHz to about 12GHz.
78. What are the applications of TRAPATT devices?
The applications are
a)Phased-array Radar systems
b)Intermediate frequency transmitters.
c)Proxity fuse sources
d)Radio altimeters
e)Microwave landing systems.
79. What are the applications of Tunnel Diode?
a)used in self excited mixers
b)High speed switching and logic operations
c)Low power oscillators.
80.What are the elements that exhibit Gunn effect?
The elements are
a)Gallium arsenide
b)Indium phosphide
c)Cadmium telluride
d)Indium arsenide.
81. What are the applications of Gunn Diode?
The applications are
a) Low and medium power oscillators
b) Used in high pump frequencies
c) Burglar alarms and aircraft rate-of-climb indicators.
82.What is negative resistance?
Negative resistance is defined as that property of a device which causes the
current through it to be 180 degree out of phase with the voltage across it.
83.What are the applications of Backward diode?
a) Video detection
b) Doppler radar
84. Why are FET’s preferred to bipolar transistor at high frequencies?
FET’s are preferred over Bipolar transistors at high frequencies as they
easily lend themselves more readily to intrgration.
85.What is the main advantage of TRAPATT over IMPATT?
TRAPATT diode has much greater efficiency than IMPATT.
86.Draw the schematic diagram of PIN diode?
1. Metallic contact
ii. -------------------------------------------------------
1. n-type Si
iii. -----------------------------------------------------
iv. Intrinsic Si
v. (Slightly n-doped)
vi. ---------------------------------------------------
1. p-type Si
vii. ------------------------------------------------------
1. Mettalic contact
87. Define GUNN EFFECT.
Guneffect was first observed by GUNN in n_type GaAs bulk diode.according
to GUNN,above some critical voltage corresponding to an electric field of
2000-4000v/cm,the current in every specimen became a fluctuating fuction of
time.The frequency of oscillation was determined mainly by the specimen and
not by the external circuit.
88. What is MESFET?
If the field effect transistor is constructed with metal semiconductor schottky
barrier diode,the device is called metal-semiconductor field effect transistor.
89.Explain stable amplification mode.
When ‘n0l’product of the device is less than about 10 ^(12)/cm^2 the
device exhibits amplification at transit time frequency rather than
spontaneous oscillation. This is called stable amplification
mode.Here n0 is the amount of doping and ‘L’ is the length.
90.What are the factors reducing efficiency of IMPATT diode?
1)Space charge effect
2)Reverse saturation current effect
3)High frequency skin effect
4)Ionization saturation effect.
91.Explain plasma formation in TRAPATT diode.
During the operation of the diode a high field avalanche zone propagates
through the depletion region and fills the layer with a dense plasma of
electrons and holes which get trapped in the low field region behind the zone.
92.What is negative resistance in gunn diode?
The carrier drift velocity increases linearly from 0 to maximum
when the electric field is increased from 0 to threshold value in
gunndiodes.When the electric field is beyond the threshold value of
3000v/cm the drift velocity is decreased and the diode exhibit
negative resistance.
93.What are the applications of GaAsMESFET.?
a,Used in microwave integrated circuits for high power, low noise
applications.
b.Used in broadband amplifier application.
94.What are the applications of TRAPATT?
a)Used in airborne
b)Marine radars.
95.What is Transferred electron effect?
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.
96.What are time parameter for TED’S
a)Domain growth time constant
b)Dielectric relaxation time
c)transit time.
97.What are the various modes of transferred electron oscillators?
a)Transit time mode
b)Quenched and delayed domain modes
c)limited space charge accumulation mode.
98.List the type of circuit used for IMPATT diode circuits.
a)Broadly tunable circuits
b)Low ‘Q’circuits
c)high ‘Q’circuits
99.What are the applications of low Q-oscillators and amplifier circuits?
a)Final output stage of FM telecommunication transmitter
b)Up converter pump
c)CW Doppler radar transmitter.
100.List some of power detecting elements?
1.Schottky diode
2.baretter
3.thermistor
4.thermocouple
101.What are microwave detector?
Microwave detectors are the instruments used to detect the
presence of microwave power is a microwave circuit.
102.Differentiate baretter and thermistor?
Baretter
1.baretter has positive
temperature coefficient.
2.it has thin wire.
3.less sensitive.
4.required less bias current
Thermistor
1.negative temp coefficient.
2.small bead of semi conductor material.
3.more sensitive.
4.require more sensitive.
103.What are tunable detector?
The tunable detectors are used to demodulate the signal and couple the
required output to high frequency scope analyzer.The low frequency
demodulated output is detected using non reciprocal detector diode monunted
in the microwave transmission line.
104. What is slotted section with line carriage?
It is a microwave sectioned coaxial line connecting a coaxial E-field probe which
penetrates inside a rectangular waveguide slotted section.The longitudinal slot is cut
along the center of the waveguide broad walls.The probe is made to move along the
slotted wall which samples the electric field propotional to probe voltage.
105. What is the main purpose of slotted section with line carriage?
1.For determination of location of voltage standing wave maxima and minima
along the line.
2.Measure the VSWR and standing wave pattern.
3.Wavelength.
4.Impedence.
5.Reflection coeffient.
6.Return loss measurement.
106. What is a VSWR meter?
VSWR meter is a highly sensitive,high gain,high theta,low noise
voltage amplifier tuned normally at fixed frequency of 1KHZ of
which microwave signals modulated.This meter indicates calibrated
VSWR reading fir any loads.
107. What is Bolometer?
It is a power sensor whose resistance change with changed
temperature as it absorb the microwave power.It is ashort thin
metallic wire sensor with positive temperature coefficient of
resistance.
108. What is calorimeter?
It is convenient device setup for measuring the high power at microwave which
involves conversion of microwave energy in to heat,absorbing the heat in a f luid
and determine the temp.
109.Mention the disadvantages of single bridge circuit ?
1.change in resistance due to mismatch at the microwave input port results in
incorrect reading
2.the thermistor is sensitive to change in the ambient temp resulting in false
readings
110. Define insertion loss?
It is defined as difference in power arriving at the terminating load .with or witout
The network in circuit
Insertion loss(db)=10 log(po/pi)
111.How will you determine the vswr and return loss in reflecto meter method?
The voltage ratio between port3 or port4 is known reflectin coefficient (T) determined
we determine VSWR and return loss as
VSWR=(1+T)/(1-T)
Return loss=-20 log(T)
112.List the different types of Impedence measurement methods?
1.Slotted line method
2.Reflectometer method
3.Reactor discontructer method
113.How do you measure microwave frequency?
1.Wavemeter method
2.Slotted line method
3.Downconversion method
114.What is a wavemeter?
It is a device used for frequency measurement in microwave.It has
cylindrical cavity with a variable short circuit termination .It changes
the resonant frequency of cavity by changing cavitylength.
115.Define dielectric constant?
It is defined by the ratio of permittivity of medium to permittivity of
freespace.
xr=x/xo=((10^-9)/36p)
116.How the S-parameter of a microwave circuit measured?
S-parameters are conveniently measured using the deschamps
method which utilizes the measured value of complex input
reflection coefficient under a number of a reactive terminations.
117. List the methods for measuring dielectric constants?
1.Waveguide method
2.cavity pertubaration method
118.What is radiation pattern?
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.
119. What is radiation efficiency?
Radiation efficiency is defined as the ratio of total power radiated to total power
accepted at its input .
120. How do you measure the polarization?
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.
121. What is spectrum analyzer?
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.
122.List the types of spectrum analyzer
Real time spectrum analyzer
Swept tuned frequency spectrum analyzer
123. List some application of spectrum analyzer.
Identifying frequency terms and their power levels
Measuring harmonic distortion in a wave
Determine type of wave modulation
Signal to noise ratio
For identifying wave distortion
124. What is network analyzer
A Network analyzer measures both amplitude and phase of a signal over a
wide frequency range. It requires accurate reference signal and a test signal
16 mark questions
1.Explain in detail about 2-cavity klystron amplifier.
-schematic circuit diagram
-mechanism of operation
-velocity modulation process
-bunching process
-calculation of efficiency, mutual conductance and voltage gain.
2. Explain about the reflex klystron.
-schematic diagram
-velocity modulation process
-power output &efficiency
-frequency characteristics.
-electronic admittance of reflex klystron.
3. Explain about TWT amplifiers.
-principle of operation
-calculation of gain
-applications
4. Explain about magnetron oscillator.
-schematic diagram
-equations of electron trajectory
-cut off magnetic field &voltage
-resonant modes&mode separation
-mechanism of oscillation.
5. Numerical problems.
-calculation of output voltage, power,efficiency for 2-cavity klystron amplifier, reflex
klystron,magnetron,TWTamplifiers.
6.What are the properties of scattering matrix for a lossless junction?
1.The product of any column of the S-matrix with conjugate of this column
equals unity.
2.The product of any column of the scattering matrix with the complex
conjugate of any
other column is zero.
7.What are ferrites devices.Explain in detail the different ferrite devices
Ferrites are ceramic like materials. These are maby by sintering a mixture of
metallic oxides
Properties
Specific resistivitieis may be used as much as 1014 greater than that of metals
Dielectric constants around 10to 15 or greater
Relative permeabilitserved.
Types of spectrum analyzer
Real time spectrum analyzer
Swept tuned frequency spectrum analyzer
Application of spectrum analyzer.
Identifying frequency terms and their power levels
Measuring harmonic distortion in a wave
Determine type of wave modulation
Signal to noise ratio
For identifying wave distortion
10.Explain in detail about network analyzer
A Network analyzer measures both amplitude and phase of a signal over a
wide frequency range. It requires accurate reference signal and a test signal
-Applications
-Types
11.Explain the different types of Impedence measurement methods?
1.Slotted line method
2.Reflectometer method
3.Reactor discontructer method
12. How do you measure microwave frequency?
1.Wavemeter method
2.Slotted line method
3.Downconversion method
Wavemeter is a device used for frequency measurement in microwave.It has
cylindrical cavity with a variable short circuit termination .It changes the resonant
frequency of cavity by changing cavitylength
13. Explain the power measuring devices baretter and thermistor?
Baretter
1.baretter has positive
temperature coefficient.
2.it has thin wire.
3.less sensitive.
4.required less bias current
Thermistor
1.negative temp coefficient.
2.small bead of semi conductor material.
3.more sensitive.
4.require more sensitive.
14.Explain in detail power detecting elements?
1.Schottky diode
2.baretter
3.thermistor
4.thermocouple
15.Explain in detail about microwave detector?
Microwave detectors are the instruments used to detect the
presence of microwave power is a microwave circuit.
Types
Crystal detector
Tunable detector
16.What is Transferred electron effect?Explian some of the TED’s?
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.
a)Domain growth time constant
b)Dielectric relaxation time
c)transit time.
17.What is negative resistance in gunn diode?Desribe the operation of GUNN
diode
Guneffect was first observed by GUNN in n_type GaAs bulk diode.according
to GUNN,above some critical voltage corresponding to an electric field of
2000-4000v/cm,the current in every specimen became a fluctuating fuction of
time.The frequency of oscillation was determined mainly by the specimen and
not by the external circuit.
The carrier drift velocity increases linearly from 0 to maximum
when the electric field is increased from 0 to threshold value in
gunndiodes.When the electric field is beyond the threshold value of 3000v/cm
the drift velocity is decreased and the diode exhibit negative resistance.
18.Explain the operation of TRAPATT diode
The Key phenomena are
a)Carrier generation by impact ionization producing a current pulse of phase
delay of 90 degree.
b)An additional phase shift introduced by the drift of carriers.
TRAPATT devices operate at frequencies from 400 MHz to about 12GHz.
The applications are
a)Phased-array Radar systems
b)Intermediate frequency transmitters.
c)Proxity fuse sources
d)Radio altimeters
e)Microwave landing systems.
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EC432 MICROWAVE ENGINEERING
TWO MARK QUESTIONS AND ANSWERS
1. Define s-matrix
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.
2What are the .Properties of s-matrix?
1.It possess symmetric property sij =sji
2.It possess unitary property
[s][s]*=[i]
3.Why is s-matrix used in MW analysis?
S matrix is used in MW analysis to overcome the problems which occurs when
H,Y,&Z parameters are used in high frequencies.
1.Equipment is not readily available to measure total voltage &total current at
the ports of the network.
2.Short and open circuits are difficult to achieve over a broad band of
frequencies.
3.Active devices,such as power transistor &tunnel diodes,frequently won’t
have stability for a short or open circuit.
4.Give ABCD matrix for a two port network
V1=A B V2
I1 C D -I2
5.What is ABCD matrix?
ABCD matrix is a transmission matrix.these parameters express voltage and
current at output in terms of those at input port.
V1=AV2-BI2
I1=CV2-DI2
6.What are the advantages of ABCD matrix?
1.They are used in power transmission lines.
2.They are very helpful in the case of cascade networks.
7.What is the Scattering matrix for N port device?
[S]= S11 S12 S13…… S1n
S21 S22 …………S2n
S31 S32 ………….S3n
. .
. .
. .
Sm1 Sm2 ………...Smm
8.Give the S matrix of uniform transmission line
S= 0 e-jbl
e-jbl 0
9.Give the properties of impedence [x]&admittance[y] matrix?
1.For a lossless junctionary y and z are symmetric .
2.[y]=[z] -1
3.Elements of matix [Z] &matrix [Y] are Frequency dependent.
10.For a loss less junction all the elements in the impedence &admittance matrices
are
Pure imaginary
11.What are the properties of scattering matrix for a lossless junctoion?
1.The product of any column of the S-matrix with conjugate of this column
equals unity.
2.The product of any column of the scattering matrix with the complex
conjugate of any
other column is zero.
12.What is transmission matrix?
When a number of microwave devices are connected in cascade.Each
junction is represented by a transmission matrix which gives the output quantities
interms of input quantities.
13.Define one port circuit.Give two examples.
A one port circuit is a circuit for which power can enter or leave through a
single wave
Guide or transmission line.
Examples:
1.Short-circuited co-axial line
14.Write the voltage matrix for an N-port microwave circuits.
V1 Z11 Z12 ….. Z1N I1
V2 Z12 Z22 …… Z2N I2
. = . . …… …. .
.
VN ZN1 ZN2 . ZNN IN
Where Zij=Elements of impedence matrix.
[Z]=Impedence martrix
15.For reciprocal media,the impedence and admittance matrices are
Symmetrical
16.For non-reciprocal media,the impedence and admittance matrices are
Ans: Asymmetrical
17.Give two examples for two port junctions.
1.The junction of two rectangular guides o ferrite devices?
Isolator Circulator Phaseshifters, Modulators, Power limiters
24. List two microwave devices using faraday rotation principles
Isolator, Circulator
25.What are powere dividers?
Power dividers are used to divide the input power into a number of smaller
amounts of power for exciting the radiating elements in an array antenna
26.What is the S-matrix of 3 port circulators?
Anticlockwise [S]= 0 1 0
0 0 1
1 0 0
Clockwise [S]= 0 0 1
1 0 0
0 1 0
27. Give the differences between Isolator and Circulator
28.What is
the S-matrix for 4
port circulators?
Clockwise
[S]= 0 0 0 1
1 0 0 0
0 1 0 0
0 0 1 0
Anticlockwise
[S] = 0 1 0 0
0 0 1 0
0 0 0 1
0 0 1 0
29.Give the S-matrix of E-plane Tee.
[S] = 0.5 0.5 0.707
0.5 0.5 -0.707
0.5 -0.707 0
30.Give the S-matrix of H-plane Tee
[S] = 0.5 -0.5 0.707
-0.5 0.5 0.707
0.707 0.707 0
31.Give the S-matrix of Magic Tee
[S] = 0 0 0.707 0.707
0 0 0.707 -0.707
0.707 0.707 0 0
0.707 -0.707 0 0
32.Give the Smatrix of directional coupler
[S] = 0 P 0 jq
P 0 jq 0
0 jq 0 P
Jq 0 P 0
Si.no Isolator Circulator
1 It is a 2 port device It is a 3 port device
2 It cannot be used as
circulator
It is used as isolator by
terminating one port
3 If input is given in port
1,output is obtained at
port 2 and vice versa
Each terminal is connected only
to the next terminal
33.Give an example for a two port MW device
Isolator is an example for a 2 port MW device
34.Give the applications of directional coupler
1.Unidirectional power measurement
2.SWR measurement
3.Unidirectional wave launching
4.Reflectometer
5.Balanced duplexer
35.What is Faraday’s rotation law?
If a circulary polarised wave is made to pass through a ferrite rod which has
been influenced by an axial magnetic field B ,then the axis of polarization gets tilted in
clockwise direction and amount of tilt depends upon the strength of magnetic field and
geometry of the ferrite.
36.Define VSWR
Voltage standing wave ratio is defined as the ratio of maximum voltage to the
minimum vottage
VSWR=Vmax/Vmin
37.What is Gyrator?
Gyrator is a two port device which provides a relative phase shift of 180 degree
for transmission from port 1 to port 2 as compared to the phase for transmission from
Port2 to port 1.
38.What is the principle of Microwave phase shifter?
When a wave propagates on a line,a phase difference prevails between any two
arbitary points along its paths.The phase difference between two points,
39.what are junctions?Give some examples
A microwave circuit consists of several microwave devices connected in some
way to achieve the desired transmission of MW signal.The interconnection of two or
more microwave may be regarded as MW junction.
Eg:Magic Tee,Hybrid Ring
40.What is Tee junction?Give two examples
In MW circuits a wave guide or coaxial junction with three independent ports is
referred to as tee junction.
Eg: E- Plane Tee,H-plane Tee
41.What is the other name for magic TEE?
Hybrid Tee
42.What is hybrid ring?
Hybrid ring consists of an annular line of proper electrical length to sustain
standing waves,to which four arms are connected at proper intervals by means of series
or parallel junctions.
43.What is the other name for Hybrid ring?
Rat-race circuit.
44.Name some wave guide components used to change the direction of the guide
through an arbitrary angle
Wave guide corner,Bend and twist
45.What are the different types of Directional coupler?
1.Two hole directional coupler
2.Be the hole directional coupler
3.Four hole directional coupler
46.What are hybrid couplers?
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.
47. What are nonreciprocal devices? Give two examples
The devices which are having the property that the forward characteristics are not
equal to the reverse characteristics are called non reciprocal devices.
48.Why isolators are called uniline?
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
49. Give some coupling parameters of directional coupler?
Coupling coefficient, Directivity, Insertion loss, Isolation
50. What are the high frequency effects in conventional tubes?
The high frequency effects in conventional tubes are
i) Circuit reactance
a)Inter electrode capacitance
b) Lead inductance
ii) Transit time effect
iii) Cathode emission
iv) Plate heat dissipation area
v) Power loss due to skin effect, radiation and dielectric loss.
51. What are the assumptions for calculation of RF power in Reflex Klystron?
i) Cavity grids and repeller are plane parallel and very large in extent.
ii) No RF field is excited in repeller space
iii) Electrons are not intercepted by the cavity anode grid.
iv) No debunching takes place in repeller space.
v) The cavity RF gap voltage amplitude V, is small compared to the dc beam
voltage VO
52. What is the condition for oscillation in Reflex klystron ?
The necessary condition for oscillation is that the magnitude of the negative real
part of the electronic admittance should not be less than the total conductance of the
cavity circuit i.e. -Ge G.
Where 1
G=Gc + Gb +G1 = ------
Rsh
Rsh effective shunt resistance
Gc copper losses of cavity
Gb beam loading conductance
G1 load conductance
53. Give the drawbacks of klystron amplifiers.
1. As the oscillator frequency changes then resonator frequency also changes
and the feedback path phase shift must be readjusted for a positive feedback.
2. The multicavity klystron amplifiers suffer from the noise caused because
bunching is never complete and electrons arrive at random at catcher cavity. Hence it is
not used in receivers.
54. What is the effect of transit time?
There are two effects.
1) At low frequencies, the grid and anode signals are no longer 180O out of
phase, thus causing design problems with feedback in oscillators.
2) The grid begins to take power from the driving source and the power is
absorbed even when the grid is negatively biased.
55. What are the applications of reflex klystron ?
1) Signal source in MW generator
2) Local oscillators in receivers
3) It is used in FM oscillator in low power MW links.
4) In parametric amplifier as pump source.
56. What is the purpose of slow wave structures used in TWT amplifiers?
Slow wave structures are special circuits that are used in microwave tubes to
reduce wave velocity in a certain direction so that the electron beam and the signal wave
can interact. In TWT, since the beam can be accelerated only to velocities that are about
a fraction of the velocity of light, slow wave structures are used.
57. How are spurious oscillations generated in TWT amplifier? State the method to
suppress it.
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.
58. State the applications of TWT.
1) Low power, low noise TWT’s used in radar and microwave receivers
2) Laboratory instruments
3) Drivers for more powerful tubes
4) Medium and high power CWTWT’S are used for communication and
radar.
59.How the klystron amplifier can act as klystron oscillator? What are the
applications of klystron amplifier?
When the klystron amplifier is given a positive feedback such that the overall
phase shift becomes zero 360° and Av = I then klystron amplifier acts as an
oscillator.
Applications:
(1) UHF TV Transmitters
(2) Long ranger radar
(3) Linear particle accelerator
(4) Troposcatter links
(5) Earth station transmitter.
60.Define phase focusing effect.
The bunching of electrons in known as “ Phase focusing effect”
This effect is important because without it, favoured electrons will fall behind the
phase change of electric field across the gaps. Such electrons are retarded at each
interaction with the R.F field in magnetron.
61.What do you mean by O-type tubes? Name some O-type tubes.
In O – type tube a magnetic field whose axis coincides with that electron
beam is used to hold the beam together as it travels the length of the tube. It is
also called as linear beam tube.
i) Helix Traveling wave tube
ii) Coupled cavity TWT
iii) Forward wave amplifier
iv) Backward wave amplifier
v) Backward wave oscillator
62. Define Transit time in Reflex klystron.
The time taken by the electron to travel into the repeller space and back to
the gap.
T =n + ¾
63. Write the parameters on which bunching depend on?
vi) Drift space should be properly adjusted.
vii) D.C anode voltage
viii) Signal amplitude should be such that proper bunching takes place.
64. Compare TWTA Klystron amplifier
Klystron amplifier TWTA
1. Linear beam or ‘O’ type device. Linear beam or ‘O’ type device
2. Uses cavities for input and Use non resonant wave circuit.
Output circuits.
3. Narrow band device due to Wide band device because use of use of
resonant cavities. Non-resonant wave circuit.
65. Give the performance Specification of Reflex klystron?
Frequency range: 2- 200 GHz
Band width: + 30 MHz for VR = + 10 V
Power output: 10 mw – 2.5W
Efficiency: 20 to 30%
66. What is CFA? State the applications of CFA.
CFA Cross Field Amplifier
CFA is a microwave power amplifier. It is a cross between TWT and
magnetron in its operation. i.e., it has a magnetron structure to provide an interaction
between crossed dc electric and magnetic fields on one hand and an RF field on the
other hand. It also uses a slow wave structure as in TWT to provide a continuous
interaction between the electron beam and a moving RF field.
Applications:
(1) Radar system
(2) Electronic counter measure.
67. State the characteristics of magnetron and of 2-cavity klystron amplifier.
Magnetron:
Operating frequencies 70 GH z
Output power 40 MW
Efficiency 40 to 70%
2-cavity klystron:
Efficiency 40%
Power output average power > 500 KW
Pulsed power > 30 MW
Power gain about 30 db.
68. What are the advantages of TWT?
1. Bandwidth is large.
2. High reliability
3. High gain
4. Constant Performance in space
5. Higher duty cycle.
69. What is meant by strapping?
The magnetron has eight or more coupled cavity resonators and hence
several modes of oscillation are possible. The oscillating frequency of
different modes are not same and are quite close to each other which
results in mode jumping. i.e., a 3 cm mode oscillation which is normal
for a particular magnetron
3
Could become a 3.05 cm------- mode oscillation. This result in
4
oscillations of reduced power at wrong frequency. To prevent this.
Strapping is used. It consists of two rings of heavy gauge wire connecting alternate
anode poles. It provides a phase difference 0f 2 radians for the modes other -mode
and thus preventing the occurrence of other modes, except the -mode .
70. State the applications of magnetrons. why magnetron is called as cross filed
device?
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.
71. What is BWO? State the applications of BWO.
A backward wave oscillator (BWO) is microwave cw oscillator with an
enormous tuning and ever all frequency coverage range.
Applications:
(i) It can be used as signal source in instruments and transmitters.
(ii) It can be used as broad band noise sources which used to confuse
enemy radar.
72. What is hull cutoff condition?
In a magnetron, the electron will just graze the anode and return towards
the cathode depends on Vo and Bo . The hull cut of magnetic equation is
Boc = (8Vo m / e) ½
-------------
b(1- a 2 / b2 )
The hull cutoff voltage equation is
Voc = e BO2 b2 (1- a2/ b2 )
…….
8m
If B0>BOe for given Vo.the electrons will not reach anode.
If Vo < Voc for a given Bo the electrons will not reach the anode.
73. What are the principal limitations of conventional negative grid electron tubes?
1) Electron transit time becomes a noticeable proportion at high frequencies.
2) Lumped electrical reactance and low Q resonant circuit.
74. What is frequency pulling and frequency pushing in magnetrons?
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.
75.What are the applications of High Q-oscillators and amplifier circuits?
They are used in
a)Low power transmitters
b)Parametric amplifier pumps
c)Police radars and intrusion alarms.
76.What are the Key phenomenon taking place in TRAPATT diode?
The Key phenomena are
a)Carrier generation by impact ionization producing a current pulse of phase
delay of 90 degree.
b)An additional phase shift introduced by the drift of carriers.
77.What is the operating frequency of TRAPATT devices?
TRAPATT devices operate at frequencies from 400 MHz to about 12GHz.
78. What are the applications of TRAPATT devices?
The applications are
a)Phased-array Radar systems
b)Intermediate frequency transmitters.
c)Proxity fuse sources
d)Radio altimeters
e)Microwave landing systems.
79. What are the applications of Tunnel Diode?
a)used in self excited mixers
b)High speed switching and logic operations
c)Low power oscillators.
80.What are the elements that exhibit Gunn effect?
The elements are
a)Gallium arsenide
b)Indium phosphide
c)Cadmium telluride
d)Indium arsenide.
81. What are the applications of Gunn Diode?
The applications are
a) Low and medium power oscillators
b) Used in high pump frequencies
c) Burglar alarms and aircraft rate-of-climb indicators.
82.What is negative resistance?
Negative resistance is defined as that property of a device which causes the
current through it to be 180 degree out of phase with the voltage across it.
83.What are the applications of Backward diode?
a) Video detection
b) Doppler radar
84. Why are FET’s preferred to bipolar transistor at high frequencies?
FET’s are preferred over Bipolar transistors at high frequencies as they
easily lend themselves more readily to intrgration.
85.What is the main advantage of TRAPATT over IMPATT?
TRAPATT diode has much greater efficiency than IMPATT.
86.Draw the schematic diagram of PIN diode?
1. Metallic contact
ii. -------------------------------------------------------
1. n-type Si
iii. -----------------------------------------------------
iv. Intrinsic Si
v. (Slightly n-doped)
vi. ---------------------------------------------------
1. p-type Si
vii. ------------------------------------------------------
1. Mettalic contact
87. Define GUNN EFFECT.
Guneffect was first observed by GUNN in n_type GaAs bulk diode.according
to GUNN,above some critical voltage corresponding to an electric field of
2000-4000v/cm,the current in every specimen became a fluctuating fuction of
time.The frequency of oscillation was determined mainly by the specimen and
not by the external circuit.
88. What is MESFET?
If the field effect transistor is constructed with metal semiconductor schottky
barrier diode,the device is called metal-semiconductor field effect transistor.
89.Explain stable amplification mode.
When ‘n0l’product of the device is less than about 10 ^(12)/cm^2 the
device exhibits amplification at transit time frequency rather than
spontaneous oscillation. This is called stable amplification
mode.Here n0 is the amount of doping and ‘L’ is the length.
90.What are the factors reducing efficiency of IMPATT diode?
1)Space charge effect
2)Reverse saturation current effect
3)High frequency skin effect
4)Ionization saturation effect.
91.Explain plasma formation in TRAPATT diode.
During the operation of the diode a high field avalanche zone propagates
through the depletion region and fills the layer with a dense plasma of
electrons and holes which get trapped in the low field region behind the zone.
92.What is negative resistance in gunn diode?
The carrier drift velocity increases linearly from 0 to maximum
when the electric field is increased from 0 to threshold value in
gunndiodes.When the electric field is beyond the threshold value of
3000v/cm the drift velocity is decreased and the diode exhibit
negative resistance.
93.What are the applications of GaAsMESFET.?
a,Used in microwave integrated circuits for high power, low noise
applications.
b.Used in broadband amplifier application.
94.What are the applications of TRAPATT?
a)Used in airborne
b)Marine radars.
95.What is Transferred electron effect?
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.
96.What are time parameter for TED’S
a)Domain growth time constant
b)Dielectric relaxation time
c)transit time.
97.What are the various modes of transferred electron oscillators?
a)Transit time mode
b)Quenched and delayed domain modes
c)limited space charge accumulation mode.
98.List the type of circuit used for IMPATT diode circuits.
a)Broadly tunable circuits
b)Low ‘Q’circuits
c)high ‘Q’circuits
99.What are the applications of low Q-oscillators and amplifier circuits?
a)Final output stage of FM telecommunication transmitter
b)Up converter pump
c)CW Doppler radar transmitter.
100.List some of power detecting elements?
1.Schottky diode
2.baretter
3.thermistor
4.thermocouple
101.What are microwave detector?
Microwave detectors are the instruments used to detect the
presence of microwave power is a microwave circuit.
102.Differentiate baretter and thermistor?
Baretter
1.baretter has positive
temperature coefficient.
2.it has thin wire.
3.less sensitive.
4.required less bias current
Thermistor
1.negative temp coefficient.
2.small bead of semi conductor material.
3.more sensitive.
4.require more sensitive.
103.What are tunable detector?
The tunable detectors are used to demodulate the signal and couple the
required output to high frequency scope analyzer.The low frequency
demodulated output is detected using non reciprocal detector diode monunted
in the microwave transmission line.
104. What is slotted section with line carriage?
It is a microwave sectioned coaxial line connecting a coaxial E-field probe which
penetrates inside a rectangular waveguide slotted section.The longitudinal slot is cut
along the center of the waveguide broad walls.The probe is made to move along the
slotted wall which samples the electric field propotional to probe voltage.
105. What is the main purpose of slotted section with line carriage?
1.For determination of location of voltage standing wave maxima and minima
along the line.
2.Measure the VSWR and standing wave pattern.
3.Wavelength.
4.Impedence.
5.Reflection coeffient.
6.Return loss measurement.
106. What is a VSWR meter?
VSWR meter is a highly sensitive,high gain,high theta,low noise
voltage amplifier tuned normally at fixed frequency of 1KHZ of
which microwave signals modulated.This meter indicates calibrated
VSWR reading fir any loads.
107. What is Bolometer?
It is a power sensor whose resistance change with changed
temperature as it absorb the microwave power.It is ashort thin
metallic wire sensor with positive temperature coefficient of
resistance.
108. What is calorimeter?
It is convenient device setup for measuring the high power at microwave which
involves conversion of microwave energy in to heat,absorbing the heat in a f luid
and determine the temp.
109.Mention the disadvantages of single bridge circuit ?
1.change in resistance due to mismatch at the microwave input port results in
incorrect reading
2.the thermistor is sensitive to change in the ambient temp resulting in false
readings
110. Define insertion loss?
It is defined as difference in power arriving at the terminating load .with or witout
The network in circuit
Insertion loss(db)=10 log(po/pi)
111.How will you determine the vswr and return loss in reflecto meter method?
The voltage ratio between port3 or port4 is known reflectin coefficient (T) determined
we determine VSWR and return loss as
VSWR=(1+T)/(1-T)
Return loss=-20 log(T)
112.List the different types of Impedence measurement methods?
1.Slotted line method
2.Reflectometer method
3.Reactor discontructer method
113.How do you measure microwave frequency?
1.Wavemeter method
2.Slotted line method
3.Downconversion method
114.What is a wavemeter?
It is a device used for frequency measurement in microwave.It has
cylindrical cavity with a variable short circuit termination .It changes
the resonant frequency of cavity by changing cavitylength.
115.Define dielectric constant?
It is defined by the ratio of permittivity of medium to permittivity of
freespace.
xr=x/xo=((10^-9)/36p)
116.How the S-parameter of a microwave circuit measured?
S-parameters are conveniently measured using the deschamps
method which utilizes the measured value of complex input
reflection coefficient under a number of a reactive terminations.
117. List the methods for measuring dielectric constants?
1.Waveguide method
2.cavity pertubaration method
118.What is radiation pattern?
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.
119. What is radiation efficiency?
Radiation efficiency is defined as the ratio of total power radiated to total power
accepted at its input .
120. How do you measure the polarization?
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.
121. What is spectrum analyzer?
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.
122.List the types of spectrum analyzer
Real time spectrum analyzer
Swept tuned frequency spectrum analyzer
123. List some application of spectrum analyzer.
Identifying frequency terms and their power levels
Measuring harmonic distortion in a wave
Determine type of wave modulation
Signal to noise ratio
For identifying wave distortion
124. What is network analyzer
A Network analyzer measures both amplitude and phase of a signal over a
wide frequency range. It requires accurate reference signal and a test signal
16 mark questions
1.Explain in detail about 2-cavity klystron amplifier.
-schematic circuit diagram
-mechanism of operation
-velocity modulation process
-bunching process
-calculation of efficiency, mutual conductance and voltage gain.
2. Explain about the reflex klystron.
-schematic diagram
-velocity modulation process
-power output &efficiency
-frequency characteristics.
-electronic admittance of reflex klystron.
3. Explain about TWT amplifiers.
-principle of operation
-calculation of gain
-applications
4. Explain about magnetron oscillator.
-schematic diagram
-equations of electron trajectory
-cut off magnetic field &voltage
-resonant modes&mode separation
-mechanism of oscillation.
5. Numerical problems.
-calculation of output voltage, power,efficiency for 2-cavity klystron amplifier, reflex
klystron,magnetron,TWTamplifiers.
6.What are the properties of scattering matrix for a lossless junction?
1.The product of any column of the S-matrix with conjugate of this column
equals unity.
2.The product of any column of the scattering matrix with the complex
conjugate of any
other column is zero.
7.What are ferrites devices.Explain in detail the different ferrite devices
Ferrites are ceramic like materials. These are maby by sintering a mixture of
metallic oxides
Properties
Specific resistivitieis may be used as much as 1014 greater than that of metals
Dielectric constants around 10to 15 or greater
Relative permeabilitserved.
Types of spectrum analyzer
Real time spectrum analyzer
Swept tuned frequency spectrum analyzer
Application of spectrum analyzer.
Identifying frequency terms and their power levels
Measuring harmonic distortion in a wave
Determine type of wave modulation
Signal to noise ratio
For identifying wave distortion
10.Explain in detail about network analyzer
A Network analyzer measures both amplitude and phase of a signal over a
wide frequency range. It requires accurate reference signal and a test signal
-Applications
-Types
11.Explain the different types of Impedence measurement methods?
1.Slotted line method
2.Reflectometer method
3.Reactor discontructer method
12. How do you measure microwave frequency?
1.Wavemeter method
2.Slotted line method
3.Downconversion method
Wavemeter is a device used for frequency measurement in microwave.It has
cylindrical cavity with a variable short circuit termination .It changes the resonant
frequency of cavity by changing cavitylength
13. Explain the power measuring devices baretter and thermistor?
Baretter
1.baretter has positive
temperature coefficient.
2.it has thin wire.
3.less sensitive.
4.required less bias current
Thermistor
1.negative temp coefficient.
2.small bead of semi conductor material.
3.more sensitive.
4.require more sensitive.
14.Explain in detail power detecting elements?
1.Schottky diode
2.baretter
3.thermistor
4.thermocouple
15.Explain in detail about microwave detector?
Microwave detectors are the instruments used to detect the
presence of microwave power is a microwave circuit.
Types
Crystal detector
Tunable detector
16.What is Transferred electron effect?Explian some of the TED’s?
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.
a)Domain growth time constant
b)Dielectric relaxation time
c)transit time.
17.What is negative resistance in gunn diode?Desribe the operation of GUNN
diode
Guneffect was first observed by GUNN in n_type GaAs bulk diode.according
to GUNN,above some critical voltage corresponding to an electric field of
2000-4000v/cm,the current in every specimen became a fluctuating fuction of
time.The frequency of oscillation was determined mainly by the specimen and
not by the external circuit.
The carrier drift velocity increases linearly from 0 to maximum
when the electric field is increased from 0 to threshold value in
gunndiodes.When the electric field is beyond the threshold value of 3000v/cm
the drift velocity is decreased and the diode exhibit negative resistance.
18.Explain the operation of TRAPATT diode
The Key phenomena are
a)Carrier generation by impact ionization producing a current pulse of phase
delay of 90 degree.
b)An additional phase shift introduced by the drift of carriers.
TRAPATT devices operate at frequencies from 400 MHz to about 12GHz.
The applications are
a)Phased-array Radar systems
b)Intermediate frequency transmitters.
c)Proxity fuse sources
d)Radio altimeters
e)Microwave landing systems.
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