Microwave:Electronics & Communication Engineering 7th semester notes

SUBJECT      :  Microwave Engineering                                        CODE                 : EC 1403

BRANCH      :  ECE                                                                                      SEM      : VII

DURATION  :  3 Hrs                                                            MAX MARKS   : 100

NOTE: ANSWER ALL QUESTIONS

SCHEME OF EVALUATION

PART – A      (10 X 2 = 20)

1. Explain Unitary Property

           The sum of products of each term of any one row or of any column of the s matrix multiplied its complex conjucate is unity.

2. What are the performance parameters of Directional Coupler

The two performance factors of DC are the Coupling Factor and Directivity. Coupling Factor defines the ratio of the amount of power coupled in coupled port to that of power at input port in decibels. Directivity is defined as the ratio of powers at the isolated port and the incident ports at decibels

3. Why we need  S matrix for microwave Analysis.

Suitable equipments are not available at microwave frequencies for the measurements of voltages and current at the ports of the networks

Short circuit and open circuit conditions are difficult at these frequencies.

Active devcies like power transistors, tunnel diodes etc don’t have suability under open /short circuit conditions.

4. Define Gunn Effect.

Gunn effect was first observed by GUNN in n-type GaAs bulk diodes.  According to GUNN above some critical voltage corresponding to an electric field of 2000-4000 v/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.

5.List out any two Non Reciprocal Devices.

     (a) Isolator (b) Circulator              

6. Why we cant use elemental based semiconductors in microwave

     (a) Maximum Saturated Drift Velocity is Limited

      (b) Applied Electric Field is also constant

7. Write the relation between S matrix and ABCD Matrix

       S₁₁= A-B-C-D/A-B+C-D

       S₂₂= -A-B-C-D/ A-B+C-D

       S₁₂= -2(AD+BC)/ A-B+C-D

       S₂₁= 2/ A-B+C-D

8. List out the various modes of Gunn Diode

Gunn oscillation mode, stable amplification mode, LSA oscillation mode and bias current osillation mode.

9. Write any four advantages of Parametric Up converter

                  Positive input impedance, Unconditionally stable, Unilateral and No circulator required

 10. What is Avalanche Transit Time devices

         Due to excess of charge carriers produced there is a delay in charge carriers moving 

          towards the other terminal of the diode.  This effect is called avalanche time effect

PART B

11.

b) Explain about Four port circulator & obtain S-matrix of Three port circulator

Four port circulator Diagram - 4

Working Principle - 5

Three port circulator Derivation - 7

S = 0    0          1

                              1    0          0

                              0    1          0         

12. ) a)  Derive and Explain Magic Tee.

S14=S41=S24=S42

S31=S13=-S23=-S32

S34=S43=0

S12=S21=0

S=        0              0           1/√2          1/√2

                         0              0           -1/√2         1/√2

                          1/√2     -1/√2        0                0

                         1/√2       1/√2        0                0              - 16

(OR)

b) Briefly explain Hybrid couplers and Rings also derive the S matrix for that.

Hybrid couplers diagram and working principle - 4

S matrix for Hybrid couplers -4

Hybrid Rings diagram and working principle -4

S matrix for Hybrid Rings -4

13. a)Derive and explain Two Hole Directional coupler in detail      

            Performance characteristics of Directional coupler -4

            S matrix derivation - 12

(OR)

b) Explain Gunn effect, RWH Theory, high field domain & Two valley model theory in details

                        Gunn effect was first observed by GUNN in n-type GaAs bulk diodes.  According to GUNN above some critical voltage corresponding to an electric field of 2000-4000 v/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.    - 4

RWH Theory: Voltage controlled Mode with diagram

                         Current controlled mode with diagram – 7

Two valley model Theory : Diagram

                                              Energy separation between valleys - 5

14. a)  Briefly explain the operation and working principles of READ diode        

                        Physical Description - 4

                        Avalanche Multiplication - 4

                        Carrier current I_o(t) and External current I_e(t)  - 4

                        Output Power and Quality Factor - 4

(OR)

(b) Write  short notes on (1) CdTe diodes (2) InP diodes

CdTe diodes construction and working principle - 8

            InP diodes construction and working principle - 8

15. (a) Explain Manley Rowe Power relation also discuss any two applications of Parametric Amplifiers

Diagram -4

Parametric amplifiers - 4

                         Parametric Up Converter -4

                         Parametric Down Converter - 4

(OR)

b) Write short notes on Microwave Amplification and Generation

 Microwave Amplification - 8

Microwave Generation - 8