Anna University, Chennai
PART-B
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 permeability is 1000
some examples of ferrite devices are Isolator Circulator Phaseshifters, Modulators, Power limiters
Circulator
S-matrix of 3 port circulators
Anticlockwise [S]= 0 1 0
0 0 1
|
Clockwise
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 |
8. Dicuss 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.
9.Explain in detail about 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.
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
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