Department of Electronics & Electrical Engg.

Question Bank: Microwave & Radar Engg.

6th Sem. Electronics & Communication Engg.

MICROWAVE TUBES

Q1 Compare the multi-cavity klystron, reflex klystron, magnetron and Traveling wave tube on

the basis of their

a) Basic construction

b) Operation

c) Applications

Q2 Explain how the oscillations are sustained in cavity magnetron with suitable sketches

assuming that the � mode oscillations already exist.

Q3 What are the various UHF limitations of vacuum tubes which limit their use at high

frequencies? Describe each of these in detail and suggest remedial measures.

Q4 Distinguish between velocity modulation and current modulation.

Q5 What is Hull cut off field?

Q6 What is phase focusing effect in magnetron?

Q7 What is a slow wave structure and why is it required?

Q8 What are reentrant cavities?

Q9 What is the purpose of strapping in magnetron?

Q10 What is electron bunching? How does it occur? Why is it also called intensity modulation?

Q11 Explain the construction and working of a multicavity klystron.

Q12 Describe the �-mode of operation of magnetron. Discuss bunching phenomenon as well.

Draw neat diagrams wherever required.

Q13 Elaborate the concept of velocity modulation, current modulation and bunching with

reference to klystron (two cavity)

Q14 What is Hull-voltage in a magnetron?

Q15 In what type of application reflex klystron is preferred & why?

Q16 List two discriminations between conventional tube and microwave tube.

Q17 What do you understand by self-consistent modes?

Q18 What is repeller protection & why is it required?

Q19 What is the need of slow wave structure in TWT?

Q20 Justify the names-control grid, screen grid, suppressor grid.

Q21 What is transit time? Why it becomes a limiting factor at lug her frequencies?

Q22 Discuss different types of vacuum tubes in lieu of their strengths and weakness.

Q23 What can be the possible solutions to the limitations of conventional tubes at high

frequencies? Which one is the best?

Q24 Elaborate the principle of working of Klystron.

Q25 Why are multicavity klystron and reflex klystron used for entirely different application?

Q26 A two cavity klystron amplifier has the following parameters:

V0=1000V, R0=40Kohm, I0=25mA, Freq=3GHz,

Gap-spacing (d) =1mm, cavities-spacing=4cm, Effective shunt impedance, excluding

beam loading=30K ohm.

a) Find the input gap voltage to give maximum voltageV2.

b) Find the voltage gain and efficiency of the amplifier neglecting the beam loading.

Q27 Why a microwave is called” Microwave”?

Q28 What is the frequency range of microwave? What limits the frequency of microwaves?

Q29 Write down the different bands in microwave range along with corresponding frequencies.

Q30 Enlist the advantages of microwave frequencies over lower frequency waves.

Q31 Make a list of important applications and the corresponding characteristics of microwave.

Q32 In which case the wavelength of the propagating microwave is greater, when it is moving

through a medium having dielectric constant=2.0 or when moving through air? Calculate

the difference of wavelength.

Q33 If a microwave having frequency 10GHz is moving out with speed of light, calculate the

corresponding wavelength.

Q34 Write a brief history of development of microwave technology.

Q35 Study manual of microwave oven.

Q36 What is frequency pulling in case of magnetrons?

Q37 List various methods of beam focusing in TWT’S

Q38 What is Velocity Modulation?

Q39 Describe the excitation of cavities.

Q40 What is microwave transition?

Q41 Ordinary low frequency circuit analysis is not adequate to describe the electrical

phenomenon-taking place at microwave frequencies, why?

Q42 Discuss the problem of transit time effect in tubes at microwave frequencies?

Q43 Why are semiconductors preferred over vacuum tubes in most applications?

Q44 Derive an expression for maximum possible theoretical efficiency of a two cavity klystron.

Q45 Explain the significance of Hull voltage in a magnetron.

Q46 Explain the principle of working of Travelling wave tube.

Q47 Find out the expression for efficiency of two cavity Klystron amplifier.

Q48 Explain with neat diagrams the following in a Magnetron:

a) Resonant Modes and their separation

b) Mechanism of Oscillation.

Q49 What do you understand by current modulation

Q50 In what type of applications reflex klystron is preferred & why?

Q51 List at least two discriminations between Klystron & TWT’s.

Q52 Discuss problem of inter electrode capacitance & lead inductance of wave frequencies.

Q53 Discuss principle of TWT along with neat sketch?

Q54 Derive an expression for maximum possible theoretical efficiency of a reflex Klystron.

Q55 List two advantages of using Microwave frequency over low frequency?

Q56 Define Transit time effect.

Q57 What is the basic difference between TWT and Magnetron?

Q58 Why at microwave frequency we talk of traveling waves with associated powers instead of

voltages and currents?

Q59 What is velocity modulation? How is it different from normal modulation? Explain how

velocity modulation is utilized in klystron amplifier.

Q60 What are slow wave structures? Explain how a helical TWT achieve amplification.

MICROWAVE SEMICONDUCTOR DEVICES

Q1. State square law of diode. Which diode exhibits this law?

Q2. Although PIN diode doesn’t exhibit negative resistance effect yet it is a very important

device at microwave frequencies. Justify.

Q3 Give the construction, working and applications of PIN diode.

Q4 Compare the main features of PIN diode and Tunnel diode.

Q5 What is Gunn effect? Explain this phenomenon using two-valley theory.

Q6 How IMPATT diode is different from all other active diodes?

Q7 Explain the operation of IMPATT diode aided by various diagrams.

Q8 Explain the basic requirements of tunneling phenomenon in Tunnel diode.

Q9 Describe briefly the quenched and delayed modes of oscillation in Gunn diode. Which

mode is more suitable and why?

Q10 What is tunneling effect? Explain the construction & working of the device, which uses

this effect, with the help of sketches. Discuss its V-I characteristics also.

Q11 Explain several modes of operation of Gunn diode with the keep of sketches.

Q12 How negative resistance is achieved in IMPATT?

Q13 What’s Gunn effect?

Q14 Compare transistors and Transfer Electron Devices (TED’S).

Q15 How depletion layer is formed in PIN diode at zero bias?

Q16 Give advantages and disadvantages of IMPATT diode.

Q17 Write down basic requirements for two-valley theory of Gunn diode.

Q18 Why FETs are preferred over Bipolar transistors at highest frequencies?

Q19 Describe the construction and operation of a PIN diode as a switch.

Q20 Explain the V-I characteristics of a Gunn diode.

Q21 Explain the use of PIN diode as a modulator.

Q22 Why FET’s are preferred over bipolar transistors at high frequencies?

Q23 What is the main advantage of using Gunn diode over IMPATT diode?

Q24 Discuss applications of PIN diode as a phase shifter.

Q25 Explain Gunn effect using two-valley theory? Also explain several modes of operation &

applications of Gunn diodes.

Q26 What is Avalanche transit time Devices?

Q27 List advantages of using Gunn diodes over IMPATT diodes.

Q28 What is the basic difference between IMPATT and TRAPATT diodes?

Q29 Describe how a tunnel diode can be used as an amplifier and as an oscillator with the

necessary circuit diagrams?

Q30 What are the applications of Tunnel diode?

Q31 Explain the physical description of read diode and the avalanche multiplication process.

Q32 Discuss the principle of negative resistances in IMPATT diode.

Q33 Explain power output and efficiency of IMPATT diode.

Q34 How is TRATATT diode different from IMPATT diode?

Q35 What are PIN Diodes? Where are they after used? Why?

Q36 Explain the use of Pin diode as a transmit/receive switch.

Q37 What are BARITT diodes?

Q38 What is the principle of operation of BARITT diode?

Q39 How is negative resistance effect of tunnel diode used in oscillators?

Q40 What do you understand by mode jumping in a magnetron?

Q41 Differentiate between a strapped and unstrapped magnetron.

Q42 Explain frequency pushing and pulling in context of magnetron.

Q43 Explain domain formation in Gunn effect devices.

Q44 What are the various frequency modes in which Gunn effect oscillator can be made to

oscillate? Explain each mode in detail.

Q45 Which microwave diode is suitable at low frequencies and why?

Q46 What happens to the performance of PIN diode above 100 MHz?

MICROWAVE MEASUREMENTS AND COMPONENTS

Q1 Describe briefly the equipment to measure impedance using slotted line.

Q2 What are non-reciprocal phase shifters? How do they differ from reciprocal phase shifters?

Q3 What is a directional coupler? Give the construction of 2-hole directional coupler.

Q4. Give the relationship between reflection coefficient and VSWR.

Q5. What are the values of reflection coefficient and VSWR in the following cases?

ii) Termination is perfectly matched

iii) Termination is a short circuit

iv) Termination is an open circuit

Q6. What are ferrites?

Q7 What is Faradays rotation? Give the construction and working of devices based on this

phenomenon.

Q8 What are the various methods of impedance matching?

Q9 Why is hybrid Tee also called magic Tee?

Q10 Why is it named magic tee also? Give construction and working in detail.

Q11 Why are resonators of irregular shape?

Q12 Write the principle of attenuator.

Q13 Differentiate reciprocal & nonreciprocal phase shifter.

Q14 What is a phase shifter? Explain its construction and principle of operation.

Q15 Differentiate E-plane Tee & H-plane Tee.

Q16 Give principle of working of resonator.

Q17 Differentiate Transmission line from wave-guides.

Q18 What is Smith chart? What is its application?

Q19 A (200+j75) Ohm load is to be matched to a 300 ohm line to give SWR=1. Calculate the

reactance of the stub and the characteristic impedance of the quarter wave transformer,

both connected to the load.

Q20 Calculate the length of a short-circuited line required to tune out the susceptance of a load

whose Y=(0.004-j0.002) S, placed on an air-dielectric transmission line of characteristic

admittance Y=00.0033S,at a frequency of 150 MHz.

Q21 A load ZL=(100-j50) ohm is connected to a line whose Z0=75ohm.Calculate

a) The point nearest to the load, at which a quarter wave transformer may be inserted

to provide correct matching.

b) The ZO of the transmission line to be used for the transformer.

Q22 A series combination having an impedances = (450+j600) ohm at 10 MHz is connected to

a 300ohm line. Calculate the position and length of a short-circuited stub designed to

match this load to the line.

Q23 A quarter wave transformer is connected directly to a 50ohm load, to match this load to a

transmission line who’s Z0=75ohm.What must be the characteristic impedance of the

matching transformer?

Q24 Calculate the length of a piece of 50ohm open-circuited line if its input admittance to be

j80x10-3 S.

Q25 With the aid of a smith chart, calculate the position and length of a short-circuited stub

matching a (180+j120) ohm load to a 300ohm transmission line. Assuming that the load

impedance remains constant, find the SWR on the mainline when the frequency is (a)

increased by 10% (b) doubled.

Q26 What is Directional coupler? Give construction of 2-hole directional coupler.

Q27 The input power in a two hole directional coupler is 1mW. The coupler has a coupling

factor of 15 db and a directivity of 30 db. Calculate the power in all the ports.

Q28 A symmetric directional coupler with infinite directivity and a forward attenuation of 20db

is used to monitor the power delivered to a load. Bolometer 1 introduces a VSWR of 2on

arm 4and bolometer 2 is matched to arm3. If bolometer1 reads 8mwand bolometer2reads

2mW, find (a) the amount of power dissipated in ZL (B) VSWR on arm2.

Q29 List the properties of ferrites that make them useful in construction of isolator’s and

circulators.

Q30 Why TEM waves cannot be propagated in wave-guides?

Q31 Why rectangular waveguides are preferred over circular waveguides in some applications?

Q32 What is magic Tee and why E-H plane is named as magic Tee?

Q33 Calculate the ratio of crossection of circular waveguide to that of a rectangular one if each

is to have same cutoff wavelength for its dominant mode.

Q34 Discuss the behaviour of ferrites in isolators and circulators.

Q35 Explain the working of H-plane Tee.

Q36 Explain the parameters of Smith Chart.

Q37 Explain Double stub matching.

Q38 Explain the principle of working of probes and loops.

Q39 A 5 dB waveguide attenuator is specified as having VSWR of 1.4. Assuming that it is

reciprocal, calculate the scattering parameters.

Q40 Define coupling factor& Directivity in case of a directional coupler.

Q41 Explain the principle of working of a Rectangular waveguide resonator.

Q42 Explain the principle of working of the following:

(a) Microwave Switch

(b) Microwave Phase Shifter.

Q43 Calculate the coupling factor and transmission factor of a 30 dB directional coupler.

Q44 List various Electronic & mechanical techniques used for measurements at microwave

frequencies?

Q45 Why TEM waves cannot be propagated in wave-guides?

Q46 List various methods that are used to carry out measurement of Low. Medium & high

microwave power.

Q47 What is the main use of coupling probes & coupling loops in wave-guides?

Q48 Calculate ratio of cross-section of circular wave-guides to that of rectangular one of each

is to have same cut off wavelength for its dominant mode?

Q49 What is VSWR & reflection Coefficient? Discuss the measurement of low, medium &

high VSWR?

Q50 Define Faraday’s rotation and also tell any device based on faraday’s rotation.

Q51 What is a Rat-race junction?

Q52 Explain how impedance can be measured using slotted line method.

Q53 Discuss methods for measurement of low and high microwave power.

Q54 Compare practical advantages and disadvantages of circular wave-guides with those of

rectangular wave-guides.

Q55 What are cavity resonators? What applications do they have? Why do they normally have

odd shapes?

Q56 Write notes on the following:

a) Probes and loops

b) Circulators and Isolators.

Q57 Discuss the quality factor& cavity resonators.

Q58 Discuss microwave bends, twists and corners.

Q59 What is matched load?

Q60 What is an E-Plane Tee?

Q61 Explain hybrid ring.

Q62 Why are attenuators needed? Why they are not a trivial part of the test setup?

Q63 Differentiate b/w fixed and variable attenuators.

Q64 Discuss insertion loss and attenuation measurement.

Q65 Show that theoretical efficiency of reflex Klystron is 27.78%.

Q66 What is a BWO? Explain its performance characteristics.

Q67 What are the applications of BWO?

Q68 Explain the function of magic Tee as a duplexer.

Q69 Explain the function of magic Tee as a mixer.

Q70 Differentiate between primary and secondary waveguides.

Q71 Explain the following terms in context of directional couplers:

a) Coupling factor

b) Directivity

c) Isolation

INTRODUCTION TO RADAR SYSTEM

Q1. How are A, B and PPI radar displays different from each other?

Q2. Calculate the maximum unambiguous range of low PRF pulse radar with a prf

of 500 Hz.

Q3. Define radar resolution cell.

Q4. What do you understand by the term dwell time?

Q5. Define multiple time around echoes.

Q6. Give the function of duplexer in radar systems.

Q7. Mention the frequencies used for radar applications.

Q8. A radar is expected to have a range of 100 Km. What is the maximum

allowable PRF for unambiguous reception.

Q9. For a radar peak transmitted power is 1MW; pulse width is 1 sec and PRF

is 1 KHz. Calculate the average transmitted power.

Q10 Enlist the factors that determine the detection range of the radar.

Q11. Enlist different applications of radar.

Q12. Enlist the limitations of PPI displays.

Q13. Draw the block diagram of pulse radar system and give the function of

each block.

Q14. Derive radar range equation.

RADAR DETECTION THEORY

Q1. For an antenna half power beam width is 3 and scan rate is 30 /sec .Calculate the

target illumination period. If R unamb=100 Km. Calculate the number of received

pulses every illumination period.

Q2. How are multiple time around echoes distinguished from unambiguous echoes?

Q3. What do you understand by the term false alarm?

Q4. Define radar cross section of target.

Q5. How does integration of radar pulses improve the detection capability of the radar?

Q6. In a radar receiver Pfa=1.05*10 -10BIF =1 MHz. What will be the

average false alarm time tolerable? For the same Pfa, how many dbs

above the rms voltage, the threshold voltage should be?

Q7. Explain the significance of radar cross section of targets.

Q8. Mention the operating frequency, power requirements and expected range of an

actual radar system.

Q9. The noise entering the IF amplifier is white Gaussian. If threshold to noise ratio is

14 dB, what will be the probability of false alarm?

Q10. Why do we prefer higher radar frequencies for meteorological radars?

Q11. With the help of suitable graph explain the radar cross section of a sphere.

Q12. Derive the radar range equation in terms of signal to noise ratio.

Q13. Briefly explain various types of losses taking place in radar systems.

Q14. Define integration improvement factor.

Q15. Derive surveillance radar range equation.

Q16. Consider s band pulse radar with the following parameters:

Peak transmitted power=300 kW

Pulse width=1msec

PRF=600 Hz

Antenna radius=6 ft.

Transmitted frequency=3000 MHz

Transmit loss=6 dB

Antenna efficiency=0.95

Calculate the maximum signal power at the range of 50 nautical miles.

Q17. Consider a radar with multiple PRF ranging using f1=13.770 KHz and

f2=14.580 KHz. Calculate the unambiguous range of each prf. Discuss the need of

multiple PRF.

Q18. Consider C band radar transmitting at a frequency of 5 GHz and having an

antenna of 6 feet radius. Pt=1 MW, pulse width=1 sec, PRF=200 Hz, equivalent

noise temperature=600 K, receiver bandwidth=1MHz, radar cross section of

target=100 m2.Calculate the available range of the radar for unity signal to noise

ratio.

Q19. A 12 GHz radar has the following parameters.

Pt=240 KW, power gain of antenna=2400, minimum detectable signal power by

receiver=10 -14 watts. Cross sectional area of radar antenna=10 m2.Find the

maximum range up to which a target of 3 m2 can be detected.

Q20. For the radar system, the following parameters are given:

Bandwidth of IF amplifier=1 MHz

Tolerable average false alarm time=15 minutes

Probability of false alarm=1.11*10 -9

Find the ratio of threshold voltage to R.M.S. value of noise voltage necessary to

achieve this false alarm time. Derive the formula used.

CW AND FM RADAR

Q1. State Doppler principle of velocity determination.

Q2. Draw the block diagram of CW radar.

Q3. Draw the block diagram of FM CW radar.

Q4. Explain the principle of working of FM CW radar. How will you modify it for

using as an altimeter?

Q5. Why is multiple frequency CW radar employed? Explain its principle of

operation.

Q6. With the help of block diagram explain the operation of FM CW altimeter.

Q7. Consider FM CW radar in which triangular shaped modulation is used. Draw the

waveforms for

(a) Transmitted signal.

(b) Beat frequency signal

When the target is approaching radar.

Q8. How will you find out sign of radial velocity with the help of CW radar?

MTI RADAR

Q1. Explain sub clutter visibility.

Q2. What do you understand by staggered PRF?

Q3. Explain the operation of MTI radar with the help of block diagram.

Q4. An MTI radar is operated at 9GHz with a PRF of 3000 pps. Calculate the first two

lowest blind speeds for this radar. .Derive the formula used.

Q5. Why is the range gating necessary in MTI radar?

Q6. What is non coherent MTI radar?

Q7. An aircraft is flying at a speed of 250 Km/h. Compute the Doppler frequency for

radar operating at a wavelength of 5 cm.

Q8. Derive an expression for blind speeds of MTI radar. Discuss the effect of large

wavelength and large PRF on lowest blind speed of target.

Q9. What are the advantages of staggered prf?

Q10. What is blind speed in MTI radar? What is the method of overcoming blind speed

problem?

Q11. Give the function of delay line canceller.

Q13. Draw and explain the operation of pulse Doppler radar.

Q14. Differentiate between MTI radar and pulse Doppler radar.

Q15. Differentiate between coherent and non coherent MTI radar.

Q16. Explain the operation of MTI radar using range gates and filters.

Q17. What is the significance of MTI radar? Describe its operation. How are moving

targets recognized on a PPI display using MTI radar?

Q18. Give the applications of MTI radar.

Q19 Give the applications of Pulse Doppler radar.

Q20. With the help of suitable block diagram explain the operation of Digital MTI

radar.

Q21. What are the limitations to MTI performance?

Q23. Explain the term Frequency agility.

Q24. Show that the product of the maximum unambiguous range and the first blind

speed v1 is equal to c /4.

Q25. What is the highest frequency on which radar can be operated if it is required to

have a maximum unambiguous range of 200 NMI and no blind speeds less than

600 Km.

Q26. Show that a triple delay line canceller is equivalent to a four pulse delay line

canceller with weights equal to the coefficients of the binomial expansion with

alternating signs.

Q27. Why does a high PRF pulse Doppler radar require a much larger improvement

factor than low PRF MTI radar, assuming comparable performance in detecting

moving targets in clutter?

Q28. Why cannot the altitude line in a high PRF pulse Doppler radar be eliminated by

range gating rather than by filtering?

Q29. A VHF radar at 220 MHz has a maximum unambiguous range of 180 nmi.

(a)What is its first blind speed?

(b)Repeat for an L band radar at 1250 MHz

Q30. What does a medium PRF pulse Doppler radar do better than a high PRF pulse

Doppler radar?

Q31. What does a high prf radar do better than a medium prf pulse Doppler radar?

TRACKING RADAR

Q1. Show different radar antenna patterns for target acquisition.

Q2. Compare the merits and demerits of the four tracking methods.

Q3. How is tracking in range achieved?

Q5. What is the simplest way to degrade the performance of conical scanning tracking

radar?

Q6. How can a target be tracked by using the phase information of a single pulse?

Q7. What do you understand by low angle tracking?

Q8. With the help of block diagram explain the operation of amplitude comparison

monopulse tracking radar for one angular coordinate.

Q9. With the help of block diagram explain the operation of amplitude comparison

monopulse tracking radar for two coordinates.

Q10. With the help of block diagram explain the operation of phase comparison

monopulse tracking radar.

Q11. With the help of block diagram explain the operation of conical scan tracking

radar.

Q12. What are the various factors which determine the accuracy of tracking radar?

Q13. Discuss the following

(a)Target acquisition

(b)Tracking in Doppler

Q14. What two measures might be taken to reduce the effects of the glint error in both

angle and range?

ELECTRONIC COUNTER MEASURES

Q1. How does an active electronic counter measure reduce the detection range of

radar?

Q2. How the reduction in bandwidth of a radar antenna can be utilized as a technique

of ECCM?

Q3. Differentiate between ECM and ECCM.

Q4. What is noise jamming as referred to ECM?

Q5. Explain the various ECM techniques in detail.

Q6. Explain the various ECCM techniques in detail.

Q7. What are the requirements of ECCM? Draw the block diagram of an ECCM

system and label the different blocks clearly. Describe its working.

STUDY OF ACTUAL RADAR SYSTEM

Q1. Enlist the features of an actual radar system.

Q2. Give a comprehensive description of an actual radar system.

NAVIGATION AIDS

Q1. Write a brief technical note on Four course radio range.

Q2. Write a technical note on LORAN A.

Q3. What are the possible errors in direction finding in radar systems?

Q4. State the functions of ground controlled approach.

Q5. How will you find the direction of arrival of a radio wave by employing a single

loop antenna?

Q6. Explain the concept of Global positioning system for navigation.

Q7. What is GCA? How is it implemented?

Q8. Explain the use of loop antenna for radio direction finding.

Q9. Write a technical note on satellite based navigation system.

Q103. What is an instrument landing system? Explain how elevation guidance is

provided in this system. Give the configuration of localizer antenna also.

Q10. Write a technical note on Four Course radio range.

Q11. Compare LORAN A and LORAN C.