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ANNAI MATHAMMAL SHEELA ENGINEERING COLLEGE

DEPARTEMENT OF ECE

MICROWAVE ENGINEERING

2 MARKS QUESTIONS AND ANSWERS

VII -TH SEM ECE

PREPARED BY

S.MANOHARAN/LECTURER

ECE

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10. Give a note on directional coupler.

Directional couplers transmission line devices that couple together to circuits in one direction, while

providing a great degree of isolation in the opposite direction

11. What are the .Properties of s-matrix?

1. It possess symmetric property sij =sji

2. It possess unitary property

[s][s]*=[i]

12. 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 thenetwork.

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 wont have stability for a shortor open circuit.

13. Give ABCD matrix for a two port network

V1=A B V2

I1 C D -I2

14. 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

15. 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

16. What is the Scattering matrix for N port device?

[S]= S11 S12 S13 S1n

S21 S22 S2n

S31 S32 .S3n

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17. 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.

18. 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 interims of input quantities.

19. 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 ortransmission line.

Examples:

1. Short-circuited co-axial line.

20. Give an example for a two port MW device

Isolator is an example for a 2 port MW device

21. Give the applications of directional coupler

1. Unidirectional power measurement

2. SWR measurement

3. Unidirectional wave launching

4. Reflectometer

5. Balanced duplexer.

22.what are junctions? Give some examples

A microwave circuit consists of several microwave devices connected in some way to achieve thedesired transmission of MW signal. The interconnection of two or more microwave may be regarded

as MW junction.

E.g.: Magic Tee, Hybrid Ring

23. What is Tee junction? Give two examples

In MW circuits a wave guide or coaxial junction with three independent ports is referred to as teejunction.

Eg: E- Plane Tee

,H-plane Tee

Hybrid Tee

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24. What is hybrid ring?

Hybrid ring consists of an annular line of proper electrical length to sustain standing waves,to whichfour arms are connected at proper intervals by means of series or parallel junctions.

25. What is the other name for Hybrid ring?

Rat-race circuit.

26. Name some wave guide components used to change the direction of the guide

through an arbitrary angle Wave guide corner, Bend and twist

27. What are the different types of Directional coupler?

1. Two hole directional coupler

2. Brethe hole directional coupler

3. Four hole directional coupler

28. What are hybrid couplers?

Hybrid couplers are interdigitated microstrip couplers consisting of four parallel strip lines with

alternate lines tied together, It has four ports. This type of coupler is called Lange hybrid coupler.

29. What are waveguide corners, bends and twists? (NOV/DEC 2007)

These wave guide components are normally used to change the direction of guide through an

arbitrary angle

30.Define coupling factor of directional coupler

It is defined as the ratio of incident power to forward power

31.Define directivity of directional coupler.

It is the ratio of forward power to the back power.

32.Define gradual twists.

Gradual twists changes the plane of polarization in a continuous fashion.

33.Define difference arm.

In E plane tee, the power output of port 3 is proportional to the difference between instantaneouspowers entering from port 1 and 2.Therefore , the third port is called difference arm.

34.What is sum arm.

In a H-plane tee, if two input waves are fed into port 1 and port 2 of the collinear arm , the output

wave at port 3 will be in phase and additive. Because of this ,third port is called as sum arm.

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UNIT 2

1. 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.

2. 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

3. 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.

4. What is the effect of transit time?

There are two effects.

1) At low frequencies, the grid and anode signals are no longer 180 degree 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 thegrid is negatively biased.

5. 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.

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iii) Forward wave amplifier

iv) Backward wave amplifier

v) Backward wave oscillator

12. 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 +

13. 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.

14. Compare TWTA Klystron amplifier

Klystron amplifier TWTA

1. Linear beam or O type device. Linear beam or O type device2. 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.

15. 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

16. 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 toprovide a continuous interaction between the electron beam and a moving RF field.

Applications:

(1) Radar system

(2) Electronic counter measure.

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17. 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

18. 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.

19. 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.

A backward wave oscillator (BWO) is microwave cw oscillator with an enormous tuning and everall frequency

20. 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.

21. 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 electronclouds.

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22.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.

23. What do you meant klystrons ?

A klystron is a vaccum tube that can be used either as a generater or as an amplifier of power at

microwave frequencies operated by the principle of velocity and current modulation

24. Define velocity modulation ?(APRIL/MAY 2008)

The variation in electron velocity in drift space is known as velocity modulation.

25 .Mention the applications of two cavity klystron.

(a) Used in Troposphere scatter transmitters

(b) Satellite communication ground ststions

Used in UHF TV transmitters

(d) Radar transmitters

26.What is drift space?

The separation between buncher and catcher grids is called as drift space.

27.Define bunching.

The electrons passing the first cavity gap at zeros of the gap voltage pass through with unchangedvelocity, those passing through the positive half cycles of gap voltage undergo an increase in

velocity: those passing through the negative half cycles of gap voltage undergo an decrease in

velocity. As a result of these, electrons bunch together in drift space. This is called bunching.

28.What is catcher cavity?

The output cavity catches energy from the bunched electron beam. Therefore, it also called as

catcher cavity.

29.Give the comparison of Klystron amplifierand TWTA

SL.NO Klystron amplifier TWTA

1. Linear beam or O type device Linear beam or O type device

2. Uses cavities for input and output circuits. Uses non-resonant wave circuit.

3. Narrow band device due to use of resonantcavities.

Wide band device because of use ofnon-resonant wave circuit.

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UNIT 3

1. What are tunable detectors?

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 mounted in the microwave transmission line.

2. 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 waveguidebroad walls. The probe is made to move along the slotted wall which samples the electric field

proportional to probe voltage.

3. 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. Impedance.

5. Reflection coefficient.

6.Return loss measurement.

4. What is a VSWR meter?

VSWR meter is a highly sensitive, high gain, high theta, low noise voltage amplifier tuned normallyat fixed frequency of 1KHZ of which microwave signals modulated. This meter indicates calibrated

VSWR reading fir any loads.5. What is Bolometer?

It is a power sensor whose resistance change with changed temperature as it absorb the microwave

power. It is a short thin metallic wire sensor with positive temperature coefficient of reistance.

6. 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.

7. 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

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8. Define insertion loss?

It is defined as difference in power arriving at the terminating load .with or without The network incircuit

Insertion loss(db)=10 log(po/pi)

9.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)

10.List the different types of Impedance measurement methods?

1.Slotted line method

2.Reflectometer method

3.Reactor discontructer method

11.How do you measure microwave frequency?

1.Wavemeter method

2.Slotted line method

3.Downconversion method

12. What is a wave meter?

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 cavity length.

13.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.

14 List the methods for measuring dielectric constants?

1. Waveguide method

2 .cavity pertubaration method

15.What is radiation pattern?

Radiation pattern is a representation of radiation characteristics of an antenna which is a function ofelevation angle azimuth angle for a constant radial distance and frequency.

16. What is radiation efficiency?

Radiation efficiency is defined as the ratio of total power radiated to total power accepted at its input

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17. How do you measure the polarization?

The polarization of an antenna is measured using transmitting mode and probing the polarization bya dipole antenna in the which the dipole is rotated in the plane of polarization and the received

voltage pattern is recorded.

18. 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.

19.List the types of spectrum analyzer

Real time spectrum analyzer

Swept tuned frequency spectrum analyzer

20. 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

21. 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

22. What is the principle by which high power measurements could be done by calorimetricmethod?(APRIL/MAY 2008

The measurement involves conversion of microwave energy into heat, absorbing this heat in a fluid

(usually water) and then measuring the temperature rice of the fluid.

24.What do you meant by slotted line?

It is a fundamental tool for microwave measurements. It consists of a section of waveguide section

or coaxial line with a longitudinal slot.This slot is roughly 1 mm wide and allows an electric field

probe to enter the waveguide for measurement of the relative magnitude of field at the location ofthe probe.

25.Define reflection coefficient.

The ratio of electric field strength of reflected and incident wave.

26.What is voltage standing wave ratio?

It is the ratio of maximum voltage to the minimum voltage.

27.Define guide wavelength.

Guide wavelength = 2x distance between two sussessive minima.

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28.What do you mean by reflection loss?

It is a measure of power loss during transmission due to the reflection of the signal as a result ofimpedance mismatch.

29.What are the contributions of insertion loss?

The insertion loss is contributed by

(i) Mismatch loss at input.

(ii) Attenuation loss through the device.

(iii) Mismatch loss at output.

30.Define scattering parameters.

Scattering parameters are defined as the ratio of outgoing waves to the incident waves.

The incident and reflected waves used to characterize a microwave circuit.

31. Distinguish between low frequency measurements and microwave measurements.

SL.NO Low frequency measurements Microwave measurements

1. At low frequency it is convenient to measure

voltage and current and use them tocalculate power.

At microwave frequencies the amplitude

of voltage and currenton a transmissionlineare the functions of distance and are

not easily measurable.

2 At low frequency ,circuits use lumped

elements.

At microwave frequencies ,the circuit

elements are distributed.

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UNIT 4

1. What are the Key phenomenon taking places 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.

2. What is the operating frequency of TRAPATT devices?

TRAPATT devices operate at frequencies from 400 MHz to about 12GHz.

3. What are the applications of TRAPATT devices?

The applications area)Phased-array Radar systems

b)Intermediate frequency transmitters.

c)Proxity fuse sources

d)Radio altimeters

e) Microwave landing systems.

4. What are the applications of Tunnel Diode?

a) used in self excited mixers

b) High speed switching and logic operations

c) Low power oscillators.

5. What are the elements that exhibit Gunn effect?

The elements are

a) Gallium arsenide

b )Indium phosphate

c) Cadmium telluride

d)Indium arsenide.

6. 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.

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7. 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.

8. What are the applications of Backward diode?

a) Video detection

b) Doppler radar

9. Why are FETs preferred to bipolar transistor at high frequencies?

FETs are preferred over Bipolar transistors at high frequencies as they easily lend themselves morereadily to integration.

10. What is the main advantage of TRAPATT over IMPATT?

TRAPATT diode has much greater efficiency than IMPATT.

11. Define GUNN EFFECT.(APRIL/MAY 2008)

Gun effect 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 everyspecimen became a fluctuating fuction of time. The frequency of oscillation was determined mainly

by the specimen and not by the external circuit.

12. What is MESFET?

If the field effect transistor is constructed with metal semiconductor schottky barrier diode,the deviceis called metal-semiconductor field effect transistor.

13.Explain stable amplification mode.When n0lproduct of the device is less than about 10 (12)/cm^2 the device exhibits amplificationat 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.

14. What are the factors reducing efficiency of IMPATT diode?(NOV/DEC 2009)

1) Space charge effect

2) Reverse saturation current effect

3) High frequency skin effect4) Ionization saturation effect.

15.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 lowfield region behind the zone

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16.What is negative resistance in gunn diode?

The carrier drift velocity increases linearly from 0 to maximum when the electric field is increasedfrom 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.

17.What are the applications of GaAsMESFET.?

a, Used in microwave integrated circuits for high power, low noise applications.

b. Used in broadband amplifier application

18.What are the applications of TRAPATT?

A )Used in airborne

b) Marine radar

19.What is Transferred electron effect?

Some materials like GaAs exhibit negative differential

mobility, when biased above a threshold value of the electric

field. This behavior is called transferred electron effect

20. What are time parameter for TEDS

a)Domain growth time constant

b)Dielectric relaxation time

c)transit time.21 .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.

22.List the type of circuit used for IMPATT diode circuits.

a)Broadly tunable circuits

b) Low Qcircuits

c) high Qcircuits

23.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.

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24.List some of power detecting elements?

1.Schottky diode

2.baretter

3.thermistor

4.thermocouple

25.What are microwave detector?

Microwave detectors are the instruments used to detect the presence of microwave power is a

microwave circuit.

26.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

27. What is parametric device?

A parametric device is one that uses a non linear reactance (capacitance or inductance ) or time-varying reactance. The word parametric is derived from the parametric excitation, which is reactive

parameter, can be used to produce capacitive or inductive excitation.

28. Give the applications of parametric amplifier.

a) space communication systems

b) Radio telescopes and

c) Torpo-receivers

29. What is meant by degenerative parametric amplifier?

It is defined as a negative resistance amplifier with the signal frequency equal to the idler frequency.

30. What is idler frequency?

The difference between the pump frequency and the signal frequency.

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UNIT 5

1. What is strip line?

The strip line consists of a central conductor called strip and two ground plates. The dominant mode

in strip line is TEM mode.

2. Define microstripline?

It consists of a conductor strip and a ground plane. The electromagnetic wave propagates in quasi

TEM mode.

3. Mention the types of losses in micro strip lines.(NOV/DEC 2009)

(i) Dielectric loss

(II) Ohmic loss and

(iii) Radiation loss

4. What is parallel strip line?

It consist of two perfectly parallel strips separated by a perfect dielectric slab of uniform thickness.

5. What do u mean by coplanar strip line?

It consists of two conducting strips on one substrate surface with one strip grounded.

6. Define partially shielded strip line?

Its strip conductor embedded in a dielectric medium, and its top and bottom ground planes have no

connection.

7. Define planar transmission?

It is a transmission line with conducting metal strips that lie entirely in parallel planes.

8. Define attenuation constant?

The sum of dielectric and the ohmic losses may be expressed as losses per unit lenth in terms of

attenuation constant

9.Write the advantages of microstripline?

(I) They have the power handling capacity of few micro watts which is quite adequate for mostmicrowave circuits.

(II) They have low loss, high dielectric constant , particularly used in the fabrication of microwave

integrated circuits

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10. Name some limitations of micro strips.

(a)Higher attenuation compared to wave guide structure. Hence it cannot be used where low loss isrequirement.

(b) At high frequencies the required dimensions are very small causing fabrication problems.

11. Mention two methods to measure the impedance (NOV?DEC 2007)

(i) Slotted line

(ii) Reflectometer

12.Name some limitations of microstrips.

(a)Higher attenuation compared to waveguide structures .Hence it cannot be used in systems whereextremely low loss is requirement.

(b) At high frequency the required dimensions are very small causing fabrication problems.

(c)Open strip suffers radiation losses.

13.Distinguish between strip line and microstrip.

SL.NO. Strip line Microstrip

1. Three conductor transmission system.i.e..

two ground planes and a strip line.

Two conductor transmission system

i.e.,one ground plane and a microstrip.

2. It supports TEM mode of propagation It supports quasi TEM mode of

propagation.

14.Advantage of coplanar strip line over conventional parallel strip line?(i)The two strips of coplanar striplines are on the same substrate for convenient connections.

(ii) Realiability is increased than conventional strip line.

(iii)Reproducibility is enhanced

(iv)Production cost is decreased.

15.Mention the various configurations in planar transmission line.

Strip lines

Microstrip

Slot line

Coplanar lines etc.

16.Mention the types of microstrip lines

(i)Embedded microstrip .

(ii)Standard inverted microstrip

(iii)Suspended microstrip

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(iv)slotted transmission line

(v)Parallel strip line

16.Mention the features of coplanar stripline.

1.Both series and shunt mounted component can be easily incorporated.

2.Coaxial to coplanar and microstrp to coplanar line transitions can be achieved easily.

3.Both balanced and unbalanced modes are possible.

17. Mention few applications of coplanar strip line.

Balanced mixers, ,balanced modulators etc. where both balanced and un balanced signals are

present.

18.What do you mean by a partially shielded strip line?

It has its strip conductor embedded in a dielectric medium, and its top and bottom planes have no

connection.

19.What are the advantages of strip lines over waveguides?

(I)Reduced bulk

(ii)Greater bandwidth

(iii)Greater compatibility.

20.What are the disadvantages of strip lines?

(i)Greater losses

(ii)Lower Q

(III)Lower power handling capacity