LATHA MATHAVAN ENGINEERING COLLEGE Alagarkovil, … -VII SEM.pdf · =2.7 780 and S 22 =0.89 -26.50. May 2012 12) A microwave ... What impedances are offered by a tuning screw on the

LATHA MATHAVAN ENGINEERING COLLEGE Alagarkovil, Madurai – 625301

Department of Electronics and Communication Engineering

FACULTY : M.Anandan ,ASP/ECE EC6701 RF and Microwave Engineering SEMESTER : VII SEM

UNIT I - TWO PORT NETWORK THEORY PART A

1) Draw the high frequency equivalent circuit of the resistor and inductor May2015

2) Mention any four differences between low and high frequency microwave circuits. May2015

3) Give the relationship between [s] and [z]. May2014

4) What are the high frequency limitations of Conventional tubes? Dec2014

5) Given [y] = [ 0 1 ] Find S parameters

[ 1 0] Dec2014

6) Define reciprocal and symmetrical networks May2013

7) What are the properties of S matrix ? May 2015

8) Draw the equivalent circuit of an inductor at radio frequency. Dec2013

9) What is ESR? Dec2013

10) What are the advantages of scattering parameters? May2012

11) Draw the equivalent circuit of practical capacitor. Dec2012

12) Mention the limitations of Z,Y and ABCD parameters at Microwave frequencies. Dec2011

13) A 5dB attenuator is specified as having VSWR of 1.2. Assuming that the

device is reciprocal, Find the S parameters. Dec2011

14) Determine the radius of the AWG 26 wire?

15) List the type of resistors?

PART B

1) Explain the concept of N port scattering matrix representation.(8) May2015

2) A four port network has the scattering matrix shown below (16)

S =

(i) Is this network lossless? (ii) Is this network Reciprocal?(iii) What is the return loss at port 1

When all other ports are terminated with matched loads?(iv) What is the insertion loss and phase

Dialog between ports 2 and 4, when all other ports are terminated with matched loads?

(v) What is the reflection coefficient seen at port 1 in a short circuit is placed at the terminal

plane of port 3, and all other ports are terminated with matched loads? 3. Explain the Scattering matrix for lossless junction. (16) May2015

4. (i) Derive Z and Y matrix formulation of Multiport network (8) May2015

(ii) State and Prove the Symmetry of S matrix for a reciprocal network (8) May2015

5. With the help of S matrix concept prove the following properties. May2014

(i)Symmetry (ii) Unitary (iii) Zero and (iv) Phase shift.

6. (i) When do you prefer transmission matrix? Obtain the ABCD matrix of a transformer with

Turns ratio of N: 1. (8) May2014

(ii) The impedance matrix of a certain lumped element network is given by Z11=4, Z12=2, Z21=2,

and Z22=4. Determine the equivalent scattering parameter matrix. (8) May2014

7. (i) Discuss the importance of low and high frequency parameters of RF two port networks(8)Dec2014

(ii) The two port devices represented by the following matrices are cascaded. Find the scattering

Matrix of the resulting device. Determine its properties (Symmetry, Reciprocity, lossless

and match). (1) [0.1 0.8] (2) [ 0.4 0.6]

[0.8 0.1] [0.6 0.4] Dec2014

8) Verify the Loss less & Reciprocity properties of two port network using scattering matrix. Dec2014

0.1900

0.8-450 0.3∟450

0

0.8-450 0 0 0.4450

0.3-450 0 0

0.6-450

0 0.4450 0.6-450

0




9. (i) Write a detailed note on ABCD parameters. (8) Dec2013

(ii) The input of an amplifier has a VSWR of 2 and the output has a VSWR of 3. Dec2013

10. Find the magnitude of the S-Parameters S11 and S22 under matched condition. (8)

Formulate S-matrix for N-port network, compute ABCD parameter for a T-network. May2013

11. (i) Explain the properties of S-matrix and hence S-matrix representation of n-port network (8)

(ii) if the impedance matrix of a simple device is [ 4 2 ]

[ 2 4], find its S-matrix May2012

12. (i) Derive the S-matrices of linear lose less Microwave devices. (8)

(ii) What are transmission matrices? Explain and obtain their relationship with S-matrix. May2012

13. (i) Formulate scattering matrix for a n-port microwave network, (8) Dec2012

(ii) Give the [ABCD] matrix for a two-port network and derive its [S] matrix (8) Dec2012

14. The S-parameters of a two-port network are given by S11 = 0.2∟900

S22= 0.2∟900

S12=0.5∟900 ,

S21= 0.5∟00.

(i)Determine whether the network is lossy or not. Dec2012

(ii) Is the network symmetrical and reciprocal? Find the insertion loss of network. (16) Dec2012

15. The S parameters of a two port network are given by S11 =0.2∟00, S22 =0.1∟0

0, S12 =0.6∟90

0,

S21 =0.6∟900.

(i) Prove that the network is reciprocal but not lossless. (ii) Find the return loss at

Port 1 when port 2 is short circuited. (16) Dec 2011

UNIT II - RF AMPLIFIERS AND MATCHING NETWORKS PART A

1) Draw the VSWR circle for reflection coefficient 1. May2015

2) Draw the Contour of Nodal Quality Factor Q=3. May2015

3) Define stability. May2014

4) What are the needs for impedance matching networks? May2014

5) Define transducer power gain. Dec 2013

6) Give the expression that relates nodal quality factor (Qn) with loaded quality factor (QL) Dec2013

7) Why impedance matching is required. What are other constrains required. May 2013

8) Draw typical output stability circle and input stability circle. May 2013

9) What are the considerations in selecting a matching network? Dec 2012

10) Define power gain of amplifier in terms of S-parameters and reflection coefficients. Dec 2012

11) Distinguish between conditional and unconditional stabilities of Amplifier. May 2012

12) A GaAs MESFET has the following parameters: S11 = 0.65∟-1540, S12 = 0.02∟40

0,

S21=2.04∟1850 and S22=0.55∟-30

0. Calculate its maximum stable power gain. May 2012

13) Write the expression for noise figure of a two port amplifier. Dec 2011

14) Define the Rollet factor?

15) What are forbidden regions? PART B

1) (i) Write the Mathematical Analysis of Amplifier Stability(8) May2015

(ii) Design a Microwave Amplifier for Maximum transducer power gain (8) May2015

2) Using Smith chart design any two possible configuration of discrete two element matching

Networks to match the source impedance ZS = (50+j25) Ω to the load ZL= (25- j50) Ω. Assume the

Characteristic impedance of Zo = 50 Ω and operating frequency of 2 GHz. (16) May2015

3) Design a matching network to match a ZL = (10+j10) Ω to a 50Ω line. Specify the values of L

and C at frequency of 1GHZ. (use smith chart). May2014

4) Derive the expressions for the following of a microstripline matching network

(a) W/h ratio (b) Total Q factor (QT) May 2014

5) (i) with reference to RF transistor amplifier, discuss the considerations for stability and gain Dec2014

(ii) Show that the noise figure of a three stage amplifier is F= F1 + F2-1 /GA1 + F3-1/GA2. Dec2014

Where F1, F2 and F3 are noise figures and GA1 and GA2 are power gains.

6) (i) Explain in detail the concept of T and Microstripline matching networks

(ii) Describe the Smith chart. How can it be used to determine unknown impedance?




7) (i) A MESFET operated at 5.7 GHz has the following S-parameters:S11 = 0.5 ∟-600 , S12 = 0.02∟0

0 ,

S21 = 6.5∟1150, S22 = 0.6∟-35

0. Verify the circuit, whether it is unconditionally stable or not? (6)

(ii) Write brief note on: (i) Operating power gain (3) (ii) Available power gain (3)

(iii) Noise figure. (4) Dec 2013

8) Discuss the Design procedure for T and π matching networks. Dec 2013

9) Discuss the smith chart approach to design the L-section and T-section matching networks. May2013

10) (i) What is a matching network? Why is this required? (8) Dec 2012

(ii) Design a ‘LC’ network for matching ZL = 10+j10 Ω to a 50 Ω transmission line at 1 Ghz. Dec 2012 11) The S-parameters for a transistor is given below. Determine its stability and draw the input

and output stability circles(Use Smith Chart).S11 = 0.385-530, S12 = 0.045900, S21=2.7780 and

S22=0.89-26.50. May 2012

12) A microwave transistor has the S parameters at 10 GHZ, with a 50 Ω reference impedance,

S11 = 0.451500, S12 = 0.01-100 , S21=2.05100 , S22=0.4-1500 . The source impedance is 20 Ω and

load impedance is 30 Ω. Compute the power gain, available gain and the transducer power gain. Dec 2011

13) An RF amplifier has the following values: Given S11 = 0.3 00, S21 = 3.5 85

0, S12 = 0.2-10

0,

S22 = 0.4-450, Vs = 5V, Zs = 40 Ω, ZL = 73 Ω, Z0= 50 Find the following quantities (a) Transducer

gain, Unilateral transducer gain, available gain, operating power gain (b) Power delivered to the load,

available power, incident power to the amplifier.

14) The output impedance of a transmitter operating at a frequency of 2Ghz is ZT=(150+j75) Ω. Using

analytical approach, design an L-section matching network, such that the maximum power is delivered

to the antenna whose input impedance is ZA=(75+j15) Ω. 15) Design a T-type matching network that transforms a load impedance ZL= (60-j30) Ω into a Zin= (10+j20)Ω

input impedance and that has a maximum nodal quality factor of 3. Compute the values for the matching

network components, assuming that matching network is required at f=1 Ghz.

UNIT III PASSIVE AND ACTIVE MICROWAVE DEVICES PART A

1) Name any two microwave passive devices which make use of Faraday rotation May 2015

2) What are matched terminators? May 2014

3) What do you mean by Faraday rotation isolator? Dec2008

4) Power at the input port is 900mw. If this power is incident on 20dB coupler with

Directivity 40dB, what is the coupled power and transmitted power. May 2013

5) Draw a structure of two hole direction coupler. Nov 2011

6) Draw the equivalent circuit of Varactor diode May 2015

7) What are the factors that reduce the efficiency of IMPATT diode? May 2014

8) What is the need for matching network ? May 2015

9) What is negative resistance in Gunn diode? May 2014

10) Mention the ideal characteristics of dielectric material in MMIC. Dec 2013

11) What is Gunn effect? Name the materials that exhibit Gunn effect? May2013

12) State the transferred electron effect. Dec 2012

13) Can Inductive elements be fabricated in MMICs? Justify your answer. May 2012

14) What impedances are offered by a tuning screw on the broad wall of rectangular waveguide,

When depth of penetration varies?

15) Write the working principle of crystal diode. PART-B

1) Draw and explain the operation of Magic Tee. Explain its application in the construction

of a 4 port circulator.(8) May 2014

2) Find the directivity in dB for a coupler if same power is applied in turn to input and output of the

coupler with output terminated in each case in a matched impedance. The auxiliary output

Readings are 450 mW and 0.710 µW.(8) May 2014

3) Draw and explain the various types of attenuators and phase shifters May2014

4) Describe the following with neat sketch (i) Magic Tee (ii) Directional coupler. May2013




5) Explain the operation of following microwave passive devices i) Circulator ii) Isolator. Dec 2013

6) Prove that it is impossible to construct a perfectly matched, lossless, reciprocal there port junction.(8) 7) Explain the working principle of Gunn diode with two valley model and plot its characteristics. May 2015

8) Explain the operating principles of varactor diode and PIN diodes (8) 9) With neat diagram explain the operation of the following devices : (i)Two hole Directional

Coupler (ii)Explain with neat diagram explain the operation of Phase shifter and show its

Phase change is 2 + 4 βl. May2015

10) What are the materials used for MMIC fabrication? Explain with neat diagrams the

Fabrication process of MMICs. May2014

11) (i) Explain any four modes of operation of a Gunn diode. (8)

12) (ii) An IMPATT diode has a drift length of 2 µm. Determine the drift time of the carriers and May 2012

the operating frequency of the IMPATT diode. (8) May2012

13) Explain the operation of following microwave passive devices.

(i) Crystal diode (8) (ii) Schottkey diode (8) 14) Show how a PIN diode is used as (i) a switch (5) (ii) an attenuator (5) (iii) a phase shifter (6)

15) (i) Explain with diagrams the applications of tuning screws.(8)

(ii) How can you synthesize a rat race hybrid coupler from magic tee? (8)

UNIT IV MICROWAVE GENERATION PART A

1) What is the role of slow wave structures in TWTs. Jun 2016

2) A helix travelling wave tube operates at 4GHZ, under a beam voltage of 10kv and beams current

of 500mA. If the helix is 25 and interaction length is 20 cm, find the gain parameter. Dec 2011

3) What is strapping with respect to magnetron? May 2010

4) Why the conventional tubes like triode, tetrode cannot generate microwave power? May2009 5) Define: Convection current of TWT. May 2014

6) Distinguish between TWT and Klystron. Dec 2013

7) What are the limitations of conventional vacuum devices? May 2015

8) Mention the major differences between TWT and Klystron. May 2015

9) Compare O-type tube and M-type tube. Dec 2012

10) List a few sensors used for Microwave power measurement. May 2012

11) What is meant by Hull cut-off voltage? Dec2008

12) Why magnetron is called as crossed field device? May 2007

13) What is meant by velocity modulation? May 2007

14) What is the condition for oscillation in Reflex klystron? Dec2007

15) Write the main demerits of single bridge power meter. Dec 2007 PART B

1) Explain the principle of operation of the Two cavity klystron with neat sketch. May 2016

A 250kW pulsed cylindrical magnetron has the following parameters. Anode voltage = 25 KV,

Peak anode current = 25A, magnetic field B = 0.35Wb/m2, Radius of cathode = 4cm, Radius of

Cylinder = 8cm.Calculate efficiency of the magnetron, cyclotron frequency, cut-off magnetic field.

2) Explain the π mode of operation of magnetron. Mention few high frequency limitations. May2015

3) (i) Show the High frequency effects in vacuum tubes. (8)

(ii) Explain the impact of frequency effects in real time vacuum tube applications. (8)

4) (i) An X band pulsed cylindrical magnetron has the following operating parameters: Anode voltage Vo= 26kV,

Beam Current Io = 27 A , Magnetic flux density Bo=0.336 Wb/m2 , Radius of cathode cylinder a = 5 cm ,

Radius of vane edge to center b = 10 cm . Determine Cyclotron angular frequency, cut off voltage for a fixed

Bo and cut off magnetic flux density for fixed Vo. Dec2014

(ii) Write a detailed note on cylindrical magnetron

5) Explain the working principle of Reflex Klystron and derive the expression of Bunching parameter Dec 2013

6) (i) Draw the cross sectional view of Magnetron tube and explain how bunching occurs in it.

Derive the expression for Hull cut-off voltage. (12) May 2012

(ii) What are practical applications of magnetron? Explain any one in detail. (4) May 2012




7) A two cavity Klystron has the following parameters. V0 =1000V, R0= 40k ohms, I0=25mA, f= 3 GHz.

Gap spacing in either cavity (d) = 1mm, Spacing between two cavities L=4 cm, Effective shunt impedance

Rsh = 30 k ohm. Calculate input gap voltage, voltage gain and efficiency. Dec 2012

8) Describe with a neat sketch the constructional details and principle of operation of a Reflex klystron.

9) (i)How can you analyze a TWTA circuit that uses a helix slow-wave non-resonant guiding structure?(8)

(ii)Explain the oscillation mechanism and the electron trajectory concept of magnetron oscillator.(8)

10) (i) Draw a neat sketch showing the constructional features of a cavity Magnetron and explain why the

Magnetron is referred to as a crossed field device.

(ii) Explain with neat sketch the operation of BWO and BWA.

UNIT V - MICROWAVE MEASUREMENTS PART A

1) Name the errors possible in VSWR measurements. May2016

2) What are the methods used to measure the attenuation at microwave frequency? Nov 2015

3) What are the errors in impedance measurement? May 2014

4) What are the sources of errors in return loss measurement using a waveguide

Reflectometer and klystron source?

5) Compare Baretter with a thermister.

6) What are the special features of a Spectrum Analyzer?

7) What is a bolometer? Give two examples. May 2008

8) What is the principle of high power measurements could be done by calorimetric method?

9) Name the two methods to measure dielectric constant of a solid.

10) Write the main demerits of single bridge power meter. Nov2008

11) Mention two methods to measure impedance. Nov 2007

12) Define return loss and write its expression. Nov 2007

13) What does the accuracy of phase measurement depend on while measuring the impedance using

Reflect meter method? Nov2008

14) What are the measurements that can be performed using (a) Spectrum Analyzer (b) Network Analyser?

15) What are the minimum and maximum values of VSWR? Give the corresponding values of

Reflection Coefficients.

PART B

1) (i) Describe how the frequency of a given source is measured.

(ii) Explain the measurement of high VSWR with the help of block diagram. May2016

2) (i) Describe how the power of a microwave generator can be measured using bolometer.(10) May2015

(ii)Calculate the SWR of a transmission system operating at 10 GHz .Assume TE10 wave transmissions

Inside a wave guide of dimensions a = 4 cm, b = 2.5 cm. The distance measured between twice

Minimum power points = 1 mm on a slotted line. (6)

3) (i) Explain SWR measurement with neat block diagram. Dec2014

(ii) Explain the procedure for measuring impedance at microwave frequency with the aid of slotted line. (8)

4) (i) Describe the measurement of power at microwave frequencies in detail.(8) May2014

(ii) Explain the procedure to measure the impedance of a load.(8)

5) With neat block diagram explain the Insertion loss and Attenuation measurements. May2008

6) With neat block diagram explain how a Network Analyzer can be used to measure the

Amplitude and phase of a signal over a wide frequency range. Also explain the measurement of

Reflection and transmission parameters and ‘ S’ parameters. (16)

7) (i) Explain the measurement of cavity ‘Q’ by slotted line method.(8)

(ii) Explain the measurements of load Impedance by reflectometer method. (8)

8) (i) Draw the experimental set up for the measurement of impedance of a discontinuity and explain.(8)

(ii) Draw the experimental setup for S parameter measurement of Magic Tee and explain.

9) Identify the applications of i) Power meter (8) ii) Spectrum Analyzer (8)

10) (i) Discuss the dielectric constant measurement using necessary block diagrams. (10)

(ii) Elaborate about S-parameters and Scattering coefficients. (6)




Unit – 1 Two Marks with Answer

1. Define s-matrix

In a microwave junction there is intersection of three or more omponents.There will be an output port ,

in addition there may be reflection from the unction of other ports. Totally there may be many combinations,

these are represented easily using a matrix called S matrix.

2. What are the Properties of s-matrix?

1. It possess symmetric property Sij = Sji

2. It possess unitary property , [s][s]*=[i]

3. Why S-matrix is used in Microwave analysis?

S matrix is used in Microwave analysis to overcome the problems which occurs when h, Y, &Z parameters

are used in high frequencies. Since, 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. 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-B I2

I1=CV2-D I2

5. 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.

6. Draw the equivalent circuit for High frequency Resistor

7. Give the properties of impedance [x] and admittance[y] matrix?

1. For a lossless functionary y and z are symmetric.

2. [y]=[z]-1

3. Elements of matrix [Z] &matrix [Y] are frequency dependent.

8. 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 S- matrix with the complex conjugate of any other column is zero.

9. What is transmission matrix?

10. State the unitary property of scattering matrix?

The row of a scattering matrix multiplied by the complex conjugate of the same row of the

Scattering matrix is one. [s][s]*=[i]

10) Write the ABCD matrix for uniform transmission line.

The ABCD Matrix for uniform transmission line is given by,




Sixteen Marks with Hints

1. Compare Z, Y ,h & ABCD parameters

2. 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.

3. It possess symmetric property Sij = Sji

4. It possess unitary property , [s][s]*=[i]

3. Explain about Transmission (ABCD) Matrix

When a number of microwave devices are connected in cascade. Each junction is represented by a transmission

matrix which gives the output quantities in terms of input quantities.

The ABCD matrix is defined as




4. Derive the S-matrix of N port network


1) What is meant by fractional bandwidth?

The fractional bandwidth is given by

2) Write the function of matching networks?

Matching networks can help stabilize the amplifier by keeping the source and load impedances in

the appropriate range. Impedance matching (or tuning) is an important issue for - Maximum power is delivered when

load is matched to line (assuming the generator is matched) - Power loss is minimized.

S/N- ratio of receiver components is increased. - Amplitude and phase errors are reduced.




3) What is function of input and output matching networks?

Input and output matching networks are needed to reduce undesired reflections and improve

the power flow capabilities.

4) What are the parameters used to evaluate the performance of an amplifier?

Key parameters of amplifier, to evaluate the performance are i. Gain and gain flatness(in dB)

ii. Operating frequency and bandwidth (in Hz) iii. Output power (in dB)

iv. Power supply requirements (in V and A) v. Input and output reflection coefficients (VSWR)

vi. Noise figure (in dB)

5) Define transducer power gain.

Transducer power gain is nothing but the gain of the amplifier when placed between source and load.

GT = Power delivered to the load

Available power from the source

6) Define Unilateral Power gain.

It is the amplifier power gain, when feedback effect of amplifier is neglected i.e.S12=0.

7) What is available Power Gain (GA) at Load?

The available power gain for load side matching (TL = T*Out) is given as,

8) Define Operating Power Gain.

The operating power gain is defined as “the ratio of power delivered to the load to the power

supplied to the amplifier”.

G = Power delivered to the load = PL

Power supplied to the amplifier Pin

9) Write a short note on feedback of RF circuit.

i. If |T|>1, then the magnitude of the return voltage wave increases called positive feedback,

which causes instability (oscillator).

ii. If |T|<1, then the return voltage wave is totally avoided (amplifier). It’s called as negative

feedback.

10) Define Stability factor ( Rolette Factor)





1. Derive the Amplifier Power Relations.

2. From the first principle, derive the constant gain circle equations

3. Explain about Gain considerations




4. Explain about Stability considerations

There are necessary conditions for a transistor amplifier to be stable based on the possible

Oscillation for input and output impedance has a negative real part as a two-sub group:

5. A Microwave transistor has the following S- parameters at 10 GHz with 50 Ω reference impedance

S11 = 0.45150o, S12 = 0.01-10

o, S21 =2.0510

o and S22 = 0.40-150

o. The source impedance is

Zs=20Ω and the load impedance is ZL=30Ω.Compute the Power gain, Available power gain and

Transducer power gain.





1. What are ferrites and give its properties?

Ferrites are ceramic like materials. These are by sintering a mixture of metallic oxides Properties

Specific resistivity’s may be used as much as 1014

greater than that of metals Dielectric constants around 10 to

15 or greater Relative permeability is 1000 . Examples of ferrite devices: Isolator Circulator Phase shifters,

Modulators, Power limiters

2. Define Gunn Effect.

Gunn effect was first observed by GUNN in 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 function of time. The frequency of oscillation was determined mainly by the specimen and not by

the external circuit.

3. 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

4. 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.

5. Give the applications of directional coupler

1. Unidirectional power measurement 2. SWR measurement

3. Unidirectional wave launching 4. Reflect meter 5. Balanced duplexer

6. What is Faraday’s rotation law?

If a circular polarized 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.

7. Define VSWR

Voltage standing wave ratio is defined as the ratio of maximum voltage to the minimum voltage .

VSWR=Vmax/Vmin

8. 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.

9. What is the principle of Microwave phase shifter?

When a wave propagates on a line, a phase difference prevails between any two arbitrary points along

its paths. The phase difference between two points,

10. 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.

11. 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.

12. List the advantages of Monolithic Microwave Integrated Circuits.

1) Small size and Weight 2) High reliability 3) Improved reproducibility 4) Improved performance

5) Eventual cost reduction when produced in large quantities.





1. Derive 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

2. Give the Smatrix of directional coupler

[S] = 0 p 0 jq

p 0 jq 0

0 jq 0 p

jq 0 p 0

3.What is negative resistance in gunn diode?Desribe the operation of Gunn diode

Gunn effect was first observed by GUNN in n_type GaAs bulk diode. The carrier drift velocity increases

linearly from 0 to maximum when the electric field is increased from 0 to threshold value in gunn diodes. When

the electric field is beyond the threshold value of 3000v/cmthe drift velocity is decreased and the diode exhibit

negative resistance.

4. Explain various modes operation of Gunn diode.


1. What are the assumptions for calculation of RF power in Reflex Klystron?

i) Cavity grids and repelled are plane parallel and very large in extent. ii) No RF field is excited in repelled

space iii) Electrons are not intercepted by the cavity anode grid. iv) No debouching takes place in repelled

space. v) The cavity RF gap voltage amplitude V, is small compared to the dc beam voltage VO

2. 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 G=Gc + Gb +G1 = 1/ Rsh ,

Rsh → effective shunt resistance ,Gc → copper losses of cavity

Gb → beam loading conductance ,G1 → load conductance




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 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.

5. 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.

6. 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.

7. How the klystron amplifier can act as klystron oscillator? When the klystron amplifier is given a positive feedback such that the overall phase shift becomes

zero 360˚ and βAv = I then klystron amplifier acts as an oscillator.

8. 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

9. What is meant by strapping?

The magnetron has eight or more coupled cavity resonators and hence several modes of oscillation are possible.

The oscillating frequencies of different modes are not same and are quite close to each other which results in

mode jumping. i.e., a 3 cm π mode oscillation which is normal for a particular magnetron 3 π could become

a 3.05 cm 3π /4mode 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 π radians for the modes other π-mode and thus preventing the occurrence of

other modes, except the π-mode.

10. 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 / b

2)

The hull cutoff voltage equation is Voc = e BO2 b

2 (1- a

2/ b

2 ) / 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.

11. 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.




12. Compare TWT and Klystron amplifier

Klystron TWT

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

2. Uses cavities for input & output circuits. 2. Use non resonant slow wave circuit.

3. Narrow band device due to Resonant

cavities

3. Wide band device because use of use

of non resonant slow wave circuit.


1. Discuss the high frequency effects in conventional tubes?

The high frequency effects in conventional tubes are

i) Circuit reactance like Inter electrode capacitance

And 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. 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.

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.Explain about the Reflex klystron.

Schematic diagram

Velocity modulation process

Power output &efficiency

Frequency characteristics.

Electronic admittance of reflex klystron.







6.

.




7.





1. How will you determine the vswr and return loss in reflectometer method?

The voltage ratio between port3 or port4 is known, reflecting coefficient () determined.

We determine VSWR and return loss as VSWR=(1+)/(1-) ,Return loss=-20 log()

2. List the different types of Impedance measurement methods?

1. Slotted line method 2. Reflectometer method 3. Reactor method

3. How do you measure microwave frequency?

1. Wave meter method 2. Slotted line method 3. Down conversion method

4. What are microwave detectors?

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

Microwave circuit.

5. Differentiate baretter and thermistor?

Baretter Thermistor

1. Barrater has positive temp.Coefficient. 1. Negative temperature coefficient.

2. It has thin wire. 2. Small bead of semi conductor material.

3. Less sensitive. 3. More sensitive.

4. Required less bias current 4. Require more sensitive

6. 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 coefficient. 6. Return loss measurement.

7. 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.

8. 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 resistance.

9. 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

10. 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.

11. List the types of spectrum analyzer

Real time spectrum analyzer and Swept tuned frequency spectrum analyzer

12. 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




13. 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


1. Explain the different types of Impedance measurement methods?

1. Slotted line method 2. Reflectometer method 3. Reactance discontinuity method

2. How do you measure microwave frequency?

1. Wave meter method 2.Slotted line method 3.Downconversion method

Wave meter 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

3. Describe Spectrum Analyzer in Detail with diagram.

A spectrum analyzer or spectral analyzer or signal analyzer is a device used to examine the spectral

composition of some electrical, acoustic, or optical waveforms. It also measures the power spectrum.

A spectrum analyzer displays signal amplitude (strength) as it varies by signal frequency.

The frequency appears on the horizontal axis, and the amplitude is displayed on the vertical axis.

To the casual observer, a spectrum analyzer looks like an oscilloscope and, in fact, some lab

instruments can function either as an oscilloscope or a spectrum analyzer.

A spectrum analyzer is used to determine whether a wireless transmitter is working according to federally-

defined standards for purity of emissions. Output signals at frequencies other than the intended

communications frequency appear as vertical lines (pips) on the display .A spectrum analyzer is also used to

determine, by direct observation, the bandwidth of a digital or analog signal.A spectrum analyzer interface is

a device that connects to a wireless receiver or a personal computer to allow visual detection and analysis of

electromagnetic signals over a defined band of frequencies. This is called panoramic reception and it is used

to determine the frequencies of sources of interference to wireless networking equipment, such as Wi-Fi and

Wireless routers.

There are analog and digital spectrum analyzers: An analog spectrum analyzer uses either a variable band-pass filter or a superheterodyne receive With a band-pass

filter, the mid-frequency is automatically tuned (shifted, swept) through the range of frequencies of which the

spectrum is to be measured. With a superheterodyne receiver, the local oscillator is swept through a range of

frequencies.

A digital spectrum analyzer computes the discrete Fourier transform (DFT), a mathematical process that transforms a

waveform into the components of its frequency spectrum.

Some spectrum analyzers (such as "real-time spectrum analyzers") use a hybrid technique where

the incoming signal is first down-converted to a lower frequency using superheterodyne techniques and then

analyzed using fast fourier transformation (FFT) techniques.

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