EC 1403 Microwave Engineering 16 Marks Questions With Answers 2014

Anna University, Chennai

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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

[S]= 0

0 1

1

0 0

0

1 0

1 0 0

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