44575327-Mwoc-Final-Lab-Manual-28-08-2010

TIRUMALA ENGINEERING COLLEGEBOGARAM (V), KEESARA (M), R.R.DIST.-501301

MWOCLABORATORY MANUAL

PREPARED BYDEEPTHI.K.V.B.L

ASSISTANT PROFESSOR-DEPT. OF ECE

DEPARTMENT OF ELECTRONICS & COMMUNICATIONENGINEERING

TIRUMALA ENGINEERING COLLEGEAUGUST - 2010

Department of ECE MWOC Lab Manual

TIRUMALA ENGINEERING COLLEGE, BOGARAM, KEESARA (M)

MICROWAVE AND OPTICAL COMMUNICATIONS

LABORATORY

PART-A

1. Reflex Klystron Characteristics.

2. Gunn Diode Characteristics.

3. Attenuation Measurement.

4. Directional Coupler Characteristics.

5. VSWR Measurement.

6. Impedance and Frequency Measurement.

7. Scattering parameters of Circulator.

8. Scattering parameters of Magic Tee.


Date:Pre-Lab:

1. Study the description of Microwave bench.

2. Learn the operation and working principle of Klystron Oscillator

3. Study the procedure of firing the Reflex Klystron

Objective:

1. To study the mode characteristics of a Reflex Klystron

2. To determine the Electronic Tuning Range ( ETR) of the Reflex Klystron

Equipment required:

1. Klystron Power supply

2. Reflex Klystron with Klystron Mount and Cooling fan

3. Isolator

4. Frequency Meter

5. Variable Attenuator

6. Detector mount

7. Wave guide stand

8. VSWR meter

10. Oscilloscope

11. BNC cables.

Experimental Microwave bench set-up:

Fig.1.1 Micro wave bench setup.


PART – A EXPERIMENT NO: 1

REFLEX KLYSTRON CHARACTERISTICS

KLYSTRON POWER SUPPLY

REFLEX KLYSTRON

OSCILLATORISOLATOR

FREQUENCY METER

DETECTOR MOUNT

POWER METER

VARIABLE ATTENUATOR

VSWR METER

OSCILLO-SCOPE


Theory:

Klystron power supply:

The Klystron power supply is used to operate the reflex Klystron tubes of S to X band

frequency range. The Klystron power supply has built in modulation facilities of Amplitude and

Frequency modulation. The Klystron power supply provides all the D.C voltages required for the

operation of reflex Klystron tube such as beam, heater and reflector voltages.

Beam supply : Voltage : +200v to 450v D.C variable

Current : 0-50 mA Max.

Repeller supply : Voltage : -270v to -20v D.C variable

Reflex Klystron:

If a fraction of the output power is fed back to the input cavity and if the loop gain has a

magnitude of unity with a phase shift of multiple of 2π , the Klystron will oscillate. The Reflex

Klystron is a single-cavity Klystron. It is a low-power generator of 10 to 500mW output at a

frequency range of 1 to 25 GHz. The efficiency is about 20-30%. This type of Klystron is widely used

in the laboratory for microwave measurements and in microwave receivers as local oscillator in

commercial, military and air borne Doppler radars.

The Reflex Klystron makes the use of velocity modulation to transform a continuous electron

beam in to microwave power. Electrons emitted from the cathode are accelerated & passed through

the positive resonator towards negative reflector, which retards and finally reflects the electrons and

the electrons turn back through the resonator. Suppose an RF-field exists between the resonators,

the electrons traveling forward will be accelerated or retarded, as the voltage at the resonator

changes in amplitude. The accelerated electrons leave the resonator at an increased velocity and the

retarded electrons leave at the reduced velocity. The electrons leaving the resonator will need

different time to return, due to change in velocities. As a result, returning electrons group together

in bunches, as the electron bunches pass through resonator, they interact with voltage at resonator

grids. If the bunches pass the grid at such a time that the electrons are slowed down by the voltage

then energy will be delivered to the resonator, and Klystron will oscillate.

The frequency is primary determined by the dimensions of resonant cavity. Hence by

changing the volume of resonator, mechanical tuning of Klystron is possible. Also a small frequency

change can be obtained by adjusting the reflector voltage. This is called Electronic Tuning.


MATCHED

TERMINATION


Mechanical and Electronic Tuning:

Mechanical tuning depends on changing the width of cavity i.e, the effective

capacitance and thus the resonant frequency of the Klystron changes. The output power remains

same with tuning.

Electronic tuning refers to change in repeller voltage causing a change in output frequency.

However, the power output also changes. A measure of electronic tuning is given by “Electronic

Tuning Sensitivity (ETS)”.

Procedure:

MODE STUDY ON OSCILLOSCOPE

1. Set up the components and equipments as shown in fig.

2. Keep position of variable attenuator at min. attenuation position.

3. Set mode selector switch to FM-MOD position, FM amplitude and FM frequency knob

at mid-position.

4. Keep beam voltage knob fully anticlockwise and reflector voltage knob to fully

clockwise position.

5. Switch “ON” the klystron power supply, Oscilloscope and cooling fan.

6. Switch “ON” Beam voltage switch and set beam voltage to 300v by beam voltage

control knob.

7. Keep amplitude knob of FM Modulation to maximum position and rotate the reflector

voltage anticlockwise to get modes on the oscilloscope.

8. By changing the reflector voltage and amplitude of FM modulation, any mode of

klystron tube can be seen on oscilloscope.

9. Draw the graph by taking reflector voltage on X-axis and output power on Y-axis.

10. Draw the graph between reflector voltage on X-axis and Frequency change on Y-axis.

11. Find the Mechanical tuning range and Electronic tuning range.



CALCULATIONS:

TABLE:

ModeAmplitude

F1 F2 V1 V2ETS=(f2-f1)/(v2-v1)

Mode 1

Mode 2

Mode 3

MODE CURVES FOR A REFLEX KLYSTRON:

Electronic tuning and output power of a Reflex Klystron:

Fig1.2 Mode characteristics of Reflex Klystron

ETS may be calculated using the relation

ETS = )(

)(

12

12

VV

ff

−−

MHz/V

Where f1, f2 being half power frequencies in GHz, and V1 and V2 are corresponding repeller

voltages for a particular mode.

INFERENCE:



Mode characteristics for Reflex Klystron are drawn.

The electronic tuning sensitivity is: ___________ .

CRITICISM:

1. Why is it necessary to cool the Klystrons?

2. Explain the significance of electronic tuning sensitivity.

3. Why the efficiency of the Klystrons is low?

4. What is the expression for the efficiency of the Reflex Klystron?

5. Differentiate between velocity modulation and current modulation.

6. Draw the admittance diagram for a Reflex Klystron oscillator

7. Draw the equivalent circuit for a Reflex Klystron oscillator

8. Oscillations in a Reflex Klystron oscillator will occur when the transit time T equals

9. Draw the Applegate diagram for a Reflex Klystron oscillator for 2 ¾ mode.

10. Mention few applications of Reflex Klystron oscillator.



WORK SPACE



Date:Pre-Lab:


2. Learn the operation and working principle of Gunn diode.

Objective:

1. To study the V-I characteristics of a Gunn Diode .

2. To determine the Threshold voltage of a Gunn Diode.

Equipment required: 1. Gunn Power supply

2. Gunn oscillator

3. Pin diode Modulator

4. Isolator

5. Frequency Meter


7. Detector mount

8. Wave guide stand

9. VSWR meter

10. Oscilloscope

11. BNC cables.


Fig.2.1. set up for the study of V-I characteristics of Gunn oscillator.

Fig.2.2 Setup for the study of output power and frequency versus bias voltage.


GUNN POWER SUPPLY

GUNN OSCILLATOR

PIN MODULATOR ISOLATOR

VARIABLE ATTENUATOR

MATCHED TERMINATION

FREQUENCY METER

GUNN POWER SUPPLY

GUNN OSCILLATORPIN

MODULATOR ISOLATORVARIABLE

ATTENUATORDETECTOR

MOUNTFREQUENCY

METER

VSWR METER

OSCILLO-SCOPE

PART – A EXPERIMENT NO: 2

GUNN DIODE CHARACTERISTICS


Theory:

The Gunn oscillator is based on negative differential conductivity effect in bulk

semiconductors. Gunn Diode has two conduction bands separated by an energy gap (greater than

thermal agitation energies). When an electron is moved to the satellite energy band, it will have

negative differential mobility. This produces the negative resistance required for the oscillations.

In a Gunn Oscillator, the Gunn diode is placed in a resonant cavity. In this case the

oscillation frequency is determined by the cavity dimension than by diode itself.

A pin modulator is used in this experiment. A square wave modulating signal is applied

through the modulator on to the microwave carrier signal.

The V-I Characteristics of the Gunn diode is obtained to identify the best operating

conditions for maximum power output at the desired operating frequency.

Procedure:

To study the V-I characteristics of Gunn Diode

1. Set up the components and equipments as shown in fig1.

2. Keep position of variable attenuator at min. attenuation position.

3. Keep the control knobs of Gunn power supply as below:

Meter switch - OFF

Gunn bias knob- Fully anticlockwise

PIN bias knob - Fully anticlockwise

PIN Mode frequency - Any position

4. Set the micrometer of Gunn oscillator for required frequency of operation.

5. Switch ON the Gunn power supply.

6. Measure the Gunn diode current corresponding to the various Gunn bias voltages through the

digital panel meter switch in steps of 0.5v. Do not exceed the bias voltage above 10 volts.

7. Plot the voltage and current readings on the graph.

8. Measure the threshold voltage which corresponds to maximum current.

CAUTION:

Do not keep Gun bias knob position at threshold position for more than 10-15 seconds.

Reading should be noted down as fast as possible, otherwise due to excessive heating, Gunn diode

may burn off.


MATCHED

TERMINATION

MATCHED

TERMINATION


CALCULATIONS:

TABLE: 1

S.No. Gunn Bias Voltage

(in Volts)

Current

(in mA)123456789

1011121314151617

Expected Graph: 0

Vth V

INFERENCE:

V-I characteristics for Gunn diode are plotted.

The Threshold voltage for Gunn diode is: __________.


Threshold Voltage

I


CRITICISM:

1. Compare and contrast Gunn diode oscillator with a Reflex Klystron oscillator.

2. Define Gunn Effect.

3. Mention the materials which can exhibit Gunn Effect.

4. List the necessary and sufficient conditions that the above materials have to satisfy

in order that Gunn Effect is observed in these materials.

5. What do you mean by R-W-H Theory?

6. List the important parameters for GaAs material.

7. List the modes of operation of Gunn Diode

8. Do you prefer Gunn oscillator or IMPATT oscillator? Justify your answer by proper

reasoning.

9. Mention few applications of Gunn diode.

10. Expand LSA.

WORK SPACE



Date:


PART- A EXPERIMENT NO: 3

ATTENUATION MEASUREMENT


Pre-Lab:1) Study the description of microwave bench.

2) Learn the difference between attenuation and insertion loss.

Objective: To Study various Attenuator values like 3dB, 6dB, 9dB etc..,.

Equipment required: Microwave source, Isolator, Frequency meter, Variable attenuator, Detector

mount, test attenuators, Cooling Fan, BNC-BNC Cable and Accessories

Theory: The Attenuator is a two port bi- directional device, which attenuates some power when

inserted into the Transmission line.

Attenuation A (in dB) = 10 log (P1/P2).

Where P1 is the Power detected by the load without the attenuator in the line and P2 is the Power

detected by the load with the attenuator.

The Attenuators consist of a resistive vane inside the waveguide to absorb microwave power

according to its position with respect to side wall of the waveguide. As Electric field maximum at

centre in TE10 mode, the attenuation will be maximum if the vane is placed at corner of waveguide.

Moving from center towards the side wall attenuation decreases. In the fixed attenuator the vane

position is fixed where as in variable attenuator, its position can be changed with the help of

micrometer of by other methods.

Following characteristics of attenuators can be studied:

1. Input VSWR

2. Insertion loss

3. Frequency sensitivity i.e. variation of attenuation with change in frequency at any

fixed position.

Procedure:



1. Connect the microwave test bench setup as shown in the fig.1

2. Switch on the AC main power and ensure that the cooling fan is on and cool air is directed

towards RK tube.

3. Switch on the RKO regulated power supply; ensure that switch position is in AM.

4. Apply maximum amplitude and frequency of 1 KHz signal.

5. Make HT on, Adjust beam voltage to 300V (approximately) so that the beam current drawn

is around 25mA.

6. Now adjust the repeller voltage very slowly, observing the CRO screen.

7. On the CRO you should get the internal tone as shown below.(Refer fig. 2)

8. Note down the values of amplitude and frequency of detected output.

9. Now remove the test attenuator and connect the microwave bench and measure the

corresponding input on the CRO.

10. Attenuation =20 log (o/p voltage/ i/p voltage).

11. Repeat the same procedure for different values of attenuators and record the values.

Experimental microwave bench setup:

Fig. 3.1. Microwave Test bench setup for the measurement of attenuation.

Fig.3.2. Detected 1KHz internal test tone.

TABLE:


MICROWAVE SOURCE ISOLATOR

FREQUENCY METER

VARIABLE ATTENUATOR

TEST ATTENUATOR

DETECTOR PROBE CRO

T

P-P amplitude


S.No Test attenuator value

Reading as obtained in step 7 (V2)

Reading as obtained in step 9 (V1)

Attenuation =20log(V2/V1)

1 3dB

2 6dB

3 9dB

4 10dB

INFERENCE:

Criticism: 1) What is VSWR?

2) What is Reflection coefficient3) Differentiate between attenuation and Insertion loss.4) Which is the dominant mode in rectangular waveguide ?5) Which is the dominant mode in circular waveguide?6) The attenuation is a function of frequency, generally becoming -------with increasing in frequency.7) 100 Watts

Power o/p= _____8) X- Band means ____ GHz to ____ GHz.9) 50 W

Power o/p

WORK SPACE


10 dB

3 dB Attenuator

Amplifier power Gain= 2


Date:


PART-A EXPERIMENT NO: 4

DIRECTIONAL COUPLER CHARACTERISTICS


Pre-Lab:1. Study the description of microwave bench.

2. Learn the operation of directional coupler.

3. Know the definition of Insertion loss, Coupling factor and directivity.

Objective:To study the function of directional coupler by measuring the following parameters.

1. Insertion loss.

2. Coupling factor

3. Directivity.

Equipment required:1. Microwave source

2. Isolator

3. Frequency meter

4. Variable attenuator

5. Detector mount

6. matched termination

7. MHD coupler

8. Cooling Fan

9. BNC-BNC Cable and Accessories.

Theory: A directional coupler is a four port device with which it is possible to measure the

incident and reflected waves separately. It consists of two transmission lines, the main arm and

auxiliary arm, electromagnetically coupled to each other as shown in fig. the power entering in the

main arm gets divided between port 2 and port 4 and almost no power comes out in port 3, power

entering at port 2 is divided between port 1 and port 3 and no power comes at port 4. Port 3 is

already terminated by default

Directional Coupler:

Fig. 4.1 Multi port directional coupler

In Fig 4.1. *. Port designations of given directional coupler.V1= Voltage measured at port 1.V2= Voltage measured at port 2.V3= Voltage measured at port 3.


MAIN ARM

AUXILLARY ARM

PORT 3

PORT 1 PORT 2

PORT 4

Terminated in matched load


V4= Voltage measured at port 4.

Fig.4.2 Detected 1KHz internal test tone.

Fig.4.3 Setup for measurement of insertion loss of given directional coupler

Fig.4.4 Setup for measurement of coupling factor for the given directional coupler


DETECTOR PROBE

CRO

Matched termination

TP-P am

plitude

MICROWAVE SOURCE ISOLATOR

FREQUENCY METER

VARIABLE ATTENUATOR

DIRECTIONAL COUPLER

PORT 1 111

PORT 2

PORT 3PORT4 4

4

Matched termination

MICROWAVE SOURCE

ISOLATOR

I

FREQUENCY METER

VARIABLE ATTENUATOR

DIRECTIONAL COUPLER

PORT 1 PORT 2

PORT 3 PORT 4

Matched termination

DETECTOR PROBE CRO

MICROWAVE SOURCE

ISOLATOR

I

FREQUENCY METER

VARIABLE ATTENUATOR

DIRECTIONAL COUPLER

PORT 1PORT 2

PORT 3 PORT 4

Matched termination

DETECTOR PROBE CRO


Fig. 4.5 Setup for measurement of directivity for the given directional coupler.

PROCEDURE:Measurement of IL:( Refer Fig.4.3)

1. Connect the microwave test bench setup as shown in the fig.

2. Switch on the AC mains power and ensure that the cooling fan is on and cool air is

directed towards RK tube.

3. Switch on the RKO regulated power supply; ensure that switch position is AM.

4. Apply maximum amplitude and frequency of 1 KHz signal.

5. Make HT on, Adjust beam voltage to 300V (approximately) so that the beam current

drawn is around 25mA.

6. Now adjust the repeller voltage very slowly, observing the CRO screen.

7. On the CRO you should get the internal tone as shown in (Fig **).

8. Note down the values of amplitude and frequency of the detected output.

9. Now remove the directional coupler and measure the corresponding input voltage (V1)

on the CRO.

10. Insertion loss is calculated by the formula IL in dB =20log(Vo/Vi)

Measurement of CF: ( Refer Fig.4.4)

11. After the measurement of IL interchange matched termination and detector probe

between ports 2 & 4. Measure the detected output at port4.

12. Coupling in dB =20 log (V4/V1).

Measurement of Directivity: (Refer Fig. 4.5)13. After the measurement of CF, reverse the direction of the given directional coupler.

Measure the detected output at port 4.

Directivity is calculated by using the formula:

Directivity in dB = 20log (V4/V1).

14. Connect matched termination to port 1 and detector probe to port 4 , observe V4.

15. Directivity in dB =20 log (V4/V2).



S.No parameter Reading obtained in

Reading obtained in step 9 (V1)

Remarks

1 INSERTION LOSS(IL)

STEP 7 (V2)V2=

IL=20Log(v2/V1)= -( ) dB

2 COUPLING FACTOR(CF)

STEP 10 (V4)V4

CF=20Log(V4/V1)

3 DIRECTIVITY STEP 12 (V4)V4

DIRECTIVITY=20 Log (v4/v1)

INFERENCE:

Criticism:

1. Mention two applications of a directional coupler.

2. An ideal direction coupler should have _____

directivity.

3. The input power is 1000W. The coupling factor is

-30 dB hence the coupled power is a ___ port device.

A directional coupler is a _____ port device.

20 dB is equivalent to a power ratio of __: __.

WORK SPACE





Date:

Pre-Lab: 1. Study the description of Microwave bench.

2. Study the concepts of standing waves. And standing wave patterns for Open circuit, Short

circuit and Matched termination lines.

Objective:

1. To study the Standing wave pattern (voltage distribution) along a slotted line when it is

i) Open-circuited

ii) Short-circuited

iii) Terminated by Z0.

iV) Arbitrary load

2. To measure Low, Medium and High VSWR.

Equipment required:

1. Micro wave power source

2. Source power supply

3. Isolator

4. Frequency Meter


6. Slotted section

7. S.S. Tuner

8. Tuned detector

8. VSWR meter

9. Wave guide stand

10. Oscilloscope

11. BNC cables.


Fig.5.1 Set up for study of voltage standing wave patterns


PART – A EXPERIMENT NO: 5VSWR MEASUREMENT

Klystron power supply SUPPLY

RKO ISOLATOR FREQUENCY METER

SLOTTED SECTION

MATCHED TERMINATION

VARIABLE ATTENUATOR

SHORT CIRCUIT TERMINATION

OPEN CIRCUIT TERMINATION

TUNING DETECTOR

WITH PROBE

INDICATING METER

SOURCE POWER SUPPLY

MICROWAVE POWER SOURCE

ISOLATOR FREQUENCY METER

SLOTTED SECTION

S.S TUNER

VARIABLE ATTENUATO

R

MATCHED TERMINATION

TUNING DETECTOR

WITH PROBE

INDICATING METER


Fig.5.2 Set up for study of Low, Medium and High VSWR.

Theory:The combination of incident and reflected waves give rise to standing waves of current and

voltage with definite maxima and minima along the line. The ratio of the maximum and minimum

magnitudes of current (or) voltage on a line having standing waves is called the standing wave ratio

and is normally abbreviated as SWR and is generally denoted by letter ‘S’.

While dealing with ratio of voltage it is abbreviated as VSWR and for current ratio it is

abbreviated as CSWR.

∴ VSWR = min

max

V

V

It is significant that VSWR is always greater than one, and when it is equal to one the line is

correctly terminated and there is no reflection.

The relation between VSWR and Reflection coefficient is given by

VSWR = S = K

K

−+

1

1

Fig.5.3 Standing waves

PROCEDURE:


E max -----------

E min ----------


(A) Standing wave patterns for: i) Open circuited ii) Short circuited

iii) Matched termination iv) Arbitrary load


2. Move the probe along the slotted line to get maximum deflection in VSWR meter.

3. Adjust the VSWR meter gain control knob or variable attenuator until the meter indicates 1.0 on

normal VSWR scale.

4. Keep all the control knobs as it is, move the probe carriage.

5. By moving the probe carriage record the VSWR meter readings in table 1, at points 0.5 cm apart

along the line.

6. Plot a curve of SWR meter reading versus distance along the line.

7. Repeat steps 5 & 6 with load–end open circuited, short circuited and match terminated and

connected with arbitrary load.

(B) Measurement of Low and Medium VSWR:


2. Move the probe along the slotted line to get maximum deflection in VSWR meter.

3. Adjust the VSWR meter gain control knob or variable attenuator until the meter indicates 1.0 on

normal VSWR scale.

4. Keep all the control knobs as it is, move the probe carriage to next minimum position. Read the

VSWR on scale.

5. Repeat the above step for change of S.S.Tuner probe depth and record the corresponding SWR.

6. If the VSWR is between 3.2 and 10, change the range dB switch to next higher position and read

the VSWR on second VSWR scale of 3 to 10.

(C) Measurement of High VSWR: (Double minimum method)


2. Set the depth of S.S. Tuner slightly more for maximum VSWR.

3. Adjust the VSWR meter gain control knob and variable attenuator to obtain a reading of 3 dB in the normal dB scale (0-10 dB) of VSWR meter.

4. Move the probe to the left on slotted line until full scale deflection is obtained on 0-10 dB scale. Note and record the probe position on slotted line let it be d1.

5. Repeat the step 3 and then move the probe right along the slotted line until full scale deflection is obtained on 0-10 dB normal dB scale. Let it be d2.

6. Replace the S.S. Tuner and termination by movable short.

7. Measure the distance between two successive minima positions of the probe. Twice this distance is guide wave length λ g.

8. Compute SWR from the following equation SWR = )( 21 dd

g

−πλ

.

CALCULATIONS:



TABLE: 1

S.No Type of load

Max. value of

standing

wave Vmax.

Min. value of

standing

wave Vmin.

VSWR=

(Vmax/Vmin)

1 ZL= ∞

Load-end open-

circuited2 ZL=0

Load-end short

circuited3 ZL=Z0

Load-end

matched load4 ZL= Arbitrary

load(Connect any

device with one

port open)

d1 d2

INFERENCE:

The standing wave patterns for Open circuit Short-circuit and Matched load are plotted by using

S.S.Tuner Low, Medium and High VSWR are measured.

Criticism:

1. Define VSWR

2. What is the range of VSWR?


o/p


3. What is the value of VSWR for i) Open circuited ii) Short circuited iii) Matched

Transmission lines.

4. What is the relation between VSWR and Reflection co-efficient?

5. Define Standing waves

6. Define Node and Anti node with respect to Standing waves.

7. What is the range of reflection coefficient?

8. Write the relation between VSWR and reflection coefficient

9. Write the expression for the input impedance of a transmission line.

WORK SPACE




PART – A EXPERIMENT NO: 6A

FREQUENCY MEASUREMENT


Date:

Pre-Lab:


2. Study the concepts of wave propagation in Rectangular wave guides, dominant mode and cut

off wave length calculations.

Objective:

To determine the frequency and wave length in a rectangular wave guide working in TE 10 mode.

Equipment required:

1. Micro wave power source

2. Source power supply

3. Isolator

4. Frequency Meter


6. Slotted section

7. Tuned detector

8. VSWR meter

9. Wave guide stand

10. Oscilloscope

11. BNC cables.


Fig.6.1 Set up for Frequency and wave length measurement

Theory:

The mode for which cut off wave length is the greatest (or) cut off frequency is the lowest is

termed as dominant mode. In case of TE waves the lowest order mode is TE10 wave which is called


KlystronPOWER SUPPLY

RKO ISOLATOR FREQUENCY METER

SLOTTED SECTION

MATCHED TERMINATION

VARIABLE ATTENUATOR

MOVABLE SHORT

TUNING DETECTOR

WITH PROBE

INDICATING METER


the dominant mode. For dominant TE10 mode rectangular waveguide λ 0, λ g and λ c are related as

below:

1 1 1 —— = —— + ---- ----- 1

λ0 2 λg

2 λc 2

where λ0 free space wavelength λg guide wavelength λc cut-off wavelength

For TE10 mode, λc = 2a where ‘a’ is broad dimension of waveguide.

PROCEDURE:

1. Set up the equipment as shown in the fig1.

2. Set up variable attenuator in the minimum attenuation position.

3. Keep the Control Knobs of Klystron power supply as below:

Beam voltage — OFF

Mod-switch — AM

Beam Voltage Knob — Fully anticlockwise

Reflector Voltage Knob — Fully clockwise

AM-Amplitude Knob — Around fully clockwise

AM-Frequency knob — Mid position.

4. Switch ‘ON’ the Klystron power supply, VSWR Meter and Cooling Fan.

5. Switch ‘ON’ the Beam Voltage Switch position and set beam voltage at 300 V.

6. Rotate the reflector voltage knob to get deflection in VSWR Meter.

7. Tune the frequency meter knob to get a ‘dip’ on the VSWR scale and note down the

frequency directly from frequency meter.

8. Replace the Termination with movable short, and detune the frequency meter.

9. Move the probe along the slotted line. The deflection in VSWR meter will vary. Move the

probe to a minimum deflection position, to get accurate reading. If necessary increase the

VSWR meter range db switch to higher position. Note and record the probe position as d1.

10. Move the probe to the next minimum position and record the probe position again as d2.

11. Calculate the guide wavelength as twice the distance between two successive minimum

positions obtained as above.

12. Measure the waveguide inner broader dimension ‘a’ which will be around 22.86 mm for X-

band.

13. Calculate the frequency by following equation.

f = λc

= c. 22

11

cg λλ+

Where c = 3 × 108 meter/sec i.e. velocity of light.



14. Verify with frequency obtained by frequency meter.

15. Above experiment can be verified at different frequencies.

CALCULATIONS:

TABLE: Measure λc=2a, calculate λ0 from equation1

S.NoFrequency (in GHz)From frequency meter

d 1 (in c m) d 2 (in c m)

Guide wavelength

(λ g)=2(d1-d2)

Operating frequency

f =0λc

1

2

INFERENCE:

Frequency and wavelengths are measured in rectangular wave guide for TE10 mode propagation.

CRITICISM:

1. Differentiate between λo, λc and λg

2. Write the inter relationship between

3. Mention the frequency range of the MW lab.

4. Mention the other methods of measuring the frequency.

5. Differentiate between operating frequency and cut off frequency.

WORK SPACE



Date:Pre-Lab:


PART- A EXPERMENT NO: 6B

IMPEDANCE MEASUREMENT



2. Study the concepts of Smith chart its properties and applications.

Objective:

To measure an unknown impedance using the smith chart with the help of microwave test

bench.

Equipment required:

1. Klystron Oscillator


3. Wave meter

4. Slotted Line section

5. Unknown Load Impedance.

6. Shorted termination plate.

Microwave test bench setup:

Fig.6.1 Set up for Impedance measurement

Theory:

Measurement of impedance is an important part of microwave engineering as it enables us to

design of impedance matching networks.


DC regulated power supply KPS

Reflex klystron oscillator

IsolatorWavemeter

Variable attenuator

Slotted section

Short circuit Termination

Detector

Unknown load impedance


There are two types of impedance matching namely, conjugate matching and Zo matching.

Conjugate matching is illustrated below:

Fig 6.1 Matching a load impedance ZL to a generator having an internal impedance ZG

(conjugate matching)

The term Zo matching is used to denote matching a load impedance to the

characteristic impedance of a transmission line.

Fig 6.2 Matching a load impedance ZL to a transmission line of characteristic impedance Zo (Zo

matching)

The input impedance of a lossless transmission line is given by

Zin = Zo [ZL + jZo Tan(βl)]/ [Zo + jZL Tan(βl)]

Procedure:


ZG = RG + j XG

ZLVG

ZG

ZL

VG

Matching Network

MATCHING NETWORK ZLZO


1. Assemble the Apparatus as shown below.

2. Adjust the position of the Traveling wave detector to the point of minimum detector

output. Record the corresponding position of the traveling detector as L1.

3. Replace the short circuit by the given unknown Load Impedance. The minima position

would have changed since the Load is changed.

4. Find the new position of the minima by moving either to right (towards Load) or to left

(towards generator). Record it L2 and Calculate

Dmin = L2 – L1 .

5. Measure the λg, Find Dmin / λg.

6. Measure the Load VSWR. Draw the VSWR circle on the Smith’s chart with the centre of the

Smith’s chart taking as the centre of the VSWR circle.

7. Move from the Short circuit Load point A on the chart along the wavelengths towards Load

(or generator) scale by distance Dmin / λg to B and join OB.

8. The point of intersection between the line OB and the VSWR circle gives the normalized

Load Zℓ = ZL/Z0.

INFERENCE:



Criticism:

1. Write the mathematical expression for the input impedance of a loss transmission line.

2. The half wave length line acts as a _______.

3. The quarter wave length line acts as a _____.

4. Define SMITH CHART.

5. A 5.2 Cm length of lossless 100Ω line is terminated in a load impedance ZL = 30+j50 Ohms

calculated TL , ΦL and the SWR along the line.

6. Define a stub.

7. What do you mean by a single stub tuner?

8. What do you mean by a double stub tuner?

9. Define scattering matrix.

10. Mention the frequency range of microwave.

WORK SPACE



Date:Pre lab :


PART-A EXPERMENT NO: 7

SCATTERING PARAMETERS OF CIRCULATOR


1. Study the description of microwave bench.

2. Study the scattering matrix and its properties.

3. Study operation of circulator.

Objective:

To study the isolator and circulator.

Equipment required:

Microwave source, Isolator, Frequency meter, Variable attenuator, Detector mount,

circulator, Cooling Fan, BNC-BNC Cable and Accessories

THEORY: CIRCULATOR:

Circulator is defined as a device with ports arranged such that energy entering a port is

coupled to an adjacent port but not coupled to the other ports.

ISOLATOR:. An isolator is a 2 port device that transfers energy from input to output with little

attenuation and from output to input with a very high attenuation

A.INSERTION LOSS:Insertion loss is the ratio of power detected at the output to the power supplied.

B. ISOLATION:Isolation is the ratio of power detected at the undesired output port to the power supplied

with all other ports is terminated with matched load.

PROCEDURE:Measurement of IL and Isolation for a 3 port circulator:

1. The scattering matrix for a 3 port circulator is given by S =

CASE 1: (To measure S11, S21 and S31)

1. Connect the set up as in fig. 1.

2. Insertion loss is given by IL = 20 log10 (V2/V1) === S21.

3. Isolation is given by I = 20 log10 (V3/V1) ====S31.



4. S11 is assumed to be zero as we are assuming impedance matched

conditions.

CASE 2: (To measure S22, S32 and S12)1. Connect the input to port 2, take the output at port 3 and terminate port 1 by

Matched Load.

2. IL = 20 log (V3/V2) =====S32.

3. I = 20 log (V1/V2) ===S12.

4. S22 = 0

CASE 3: ( To measure S33,S13 and S23)1. Connect the input to port 3, take the output at port 1 and terminate port 2 by

Matched Load.

2. IL = 20 log (V1/V3) =====S13.

3. I = 20 log (V1/V2) ===S23.

4. S33 = 0 (Assumed impedance matching throughout).

Finally form the scattering matrix for a 3 port circulator.

Fig.7.1 Setup for measurement of S-Matrix for a 3 port circulator

INFERENCE:

The general scattering matrix for 3 port circulator is given by


MICROWAVE SOURCE

ISOLATOR

FREQUENCY

METERVARIABLE

ATTENUATOR

PORT 1 PORT 2

PORT 3

Matched termination

DETECTOR PROBE

CRO


Now substitute the ratio for the scattering elements (from your measurements) and obtain the

practical S-matrix.

CRITICISM:

1. What are ferrites?

2. What do you mean by Faraday rotation?

3. Mention few materials for ferrite applications.

4. Dedifferentiate between isolator and circulators.

5. What do you mean by gyromagnetic resonance?

WORK SPACE





Date:Pre-Lab :

1. Study the description of microwave bench.

2. Study the scattering matrix and its properties.

3. Study operation of MAGIC Tee.

Objective:

To study the Magic Tee.

Equipment required:

Microwave source, Isolator, Frequency meter, Variable attenuator, and Detector mount,

Magic Tee, Cooling Fan, BNC-BNC Cable and Accessories.

THEORY: The device magic T is a combination of the E and H planes T’s. Arm 3 is the H arm and

arm 4 is the E arm. If the power is fed, into arm 3 the electric field divides equally between arm 1

and 2 with the same phase and no electric field exists at arm 4. Similarly, if the power is fed into

arm 4 the electric field divides equally between arm 1 and 2 with 180 phase and no electric field

exists at arm 3. If power is fed into arm 1 the electric field gets divided equally between arms 3 and

4, no power exists at port 1.

In a nutshell, in a magic T – the opposite arms will not see eye-to eye.

4

E- ARM 1 2

H-ARM 3

Fig.8.1 Schematic representation of magic –T

The general S- matrix for magic T is

S11 S12 S13 S14

S21 S22 S23 S24

S31 S32 S33 S34

S41 S42 S43 S44


S =

PART-A EXPERMENT NO: 8SCATTERING PARAMETERS OF MAGIC-TEE


Applying lossless, reciprocal and impedance matched conditions, the final S-matrix for magic

T (with the above port designations) is given ass

0 0 1/ 2 1/ 2 S= 0 0 1/ 2 -1/ 2

1/ 2 1/ 2 0 0 1/ 2 -1/ 2 0 0

Measurement of scattering matrix for MAGIC- T

PROCEDURE:

1. Connect the setup as shown in fig.2, by passing the magic T. Measure the peak-to-peak

amplitude of the detected output, with the help of detected probe and CRO, at the end of the

variable attenuator. Designate this as input to magic –T(vin).

2. Now connect the setup as in fig.2.

a) Measure V2 (port 3 and 4 should be terminated with matched loads). Calculate

20log(V2/Vin ) this is S21.

b) Measure V3 (port 2 and 4 should be terminated with matched loads). Calculate

20log(V3/Vin) this is S31.

c) Measure V4 (port 2 and 3 should be terminated with matched loads). Calculate 20log(V4/Vin)

this is S41.

d) It is assumed impedance matched, hence S11=0 and the first column in S-matrix is now

obtained.

Repeat this procedure and obtain scattering elements is 2nd, 3rd and 4th columns of S-matrix

for magic –T.

Finally form the Scattering matrix for MAGIC-TEE.

Microwave test bench setup:

Fig.8.1 Setup for measurement of S-Matrix for a Magic -T


MICROWAVE SOURCE

ISOLATOR

I

FREQUENCY METER

VARIABLE ATTENUATOR

PORT 1 PORT 3

DETECTOR PROBE CRO

MAGIC T

PORT 4

PORT 2

Matched termination

Matched termination


INFERENCE:

CRITICISM:

1. Define the E- plane waveguide Tee junction.

2. Define the H- plane waveguide Tee junction.

3. Define the Hybrid junction.

4. Define the hybrid ring.

5. What do you mean by WILKINSON power divider?



WORK SPACE



PART – B

1. Characterization of LED.

2. Characterization of Laser Diode.

3. Intensity modulation of Laser output through an optical fiber.

4. Measurement of NA.

5. Measurement of Losses for Analog Optical link.



Date:

Pre-Lab: 1. Study the optical communication kit.

2. Study about the light sources and optical sources.

Objective:

1. To study relationship between the LED dc forward current and the LED optical power

output.

2. To determine the linearity of the device at 660 nm.

3. To determine conversion efficiency of the LED 660nm.

Equipment required: optical communication kit, Digital multi meters.

THEORY:

LED’s and laser diodes are the commonly used sources in optical communication systems,

whether the system transmits digital or analog signals. In the case of analog transmission, direct

intensity modulation of the optical source is possible, provided the optical output from the source can

be varied linearly as a function of the modulating electrical signal amplitude. LED’s have a linear

optical output with relation to the forward current over certain region of operation. It may be

mentioned that in many low cost and small bandwidth applications LED’s at 660nm, 850 nm and

1300 nm are popular. While direct intensity modulation is simple to realize, higher performance is

achieved by FM modulating the base-band signal prior to intensity modulation.

This relationship between an LED optical output Po and the LED forward current If is given by

Po =K If (over a limited range), where K is constant.

PROCEDURE:

1. Connect the circuit as shown in diagram 1. Connect one end of cable 1(1 m) to

the FO LED1 (660 nm) port and the other end to the FO PIN port (power

meter).

2. Switch on the power supply.

3. Adjust the potentiometer Po, so that the power meter reads 15.0 dBm.

4. Connect the digital mutimeter at V01 terminal provided at FO LED 1 and

measure voltage V01 in milli volts.


PART-B EXPERIMENT NO: 1CHARACTERIZATION OF LED


If1 =V01 (mV)/R1 in mA.

Where If1 =660 nm LED forward current.

R1= Internal Resistance (100 Ohm)

5. Adjust the potentiometer PO to the extreme anti clock wise position to reduce

If1 to 0

6. Slowly turn the potentiometer Po clockwise to increase If1. The power meter

should read -30.0 dB approximately. From here vary the pot PO in suitable

steps and note the V01 and note the power meter reading, Po, record up to the

extreme clockwise position and note down the values in table 2.1.

7. Switch OFF the power supply.

8. Repeat the complete experiment for Fo LED2 and tabulate the reading in table

2.2 for V02 and Po. If2 = V02 (mV)/R2 in mA. (Apply the conation of 2.2 dB

discussed in experiment for the 850 nm LED).

Where If2 =850 nm LED forward current.

R2 = Internal resistance (100 Ohms).

Table:

660 nm LED

S.NO V01(mV) If1=(V01/100) mA Po(dBm) P0(mW)

1

2

3

4

5

6

7

8

9

10

11

12

13

14



INFERNCE:

From this experiment we can observe that the LED at 660 nm have a linear response for Po

vs If. By selecting this region of If for operation, a linear intensity modulation system for signal

transmission may be designed. We choose quiescent DC operating current of 10mA (approx.) for the

660 nm .

Criticism:

1) Define optical communications.

2) Compute the advantages and disadvantages of optical fiber over metallic cables.

3) Define light source and optical power.

4) The human eye can detect only those light waves between approximately

_____nm and ___nm.

5) Mention few semiconductor materials used in led construction and their

respective output wave lengths.

6) Differentiate between homo junction LEDs and hetero junction LEDs.

7) Define process called lasing.

8) Mention advantages of ILDs over LEDs.

9) Mention disadvantages of ILDs over LEDs.

10)Determine the optical power 10mW in dBm and dBu



WORK SPACE



Date:Pre-Lab:

1. Study the optical communication kit.

2. Study about the light sources and optical sources.

Objective:

The aim of the experiment is to study

1. Optical power (P0 ) of a Laser Diode vs Forward current(IF )

2. Monitor Photodiode current( Im ) vs Laser optical power output(Po)

Equipment required:

1. Optical communication kit

2. Digital multimeters.

THEORY:

LEDS and laser diodes are the commonly used sources in optical communication systems,

whether the system transmits digital or analog signals. In the case of analog transmission, direct

intensity modulation of the optical output with relation to the forward current over a certain region of

operation. It may be mentioned that in many low cost, short haul and small band width applications,

LEDs at 660 nm, 850 nm and 1300 nm are popular. While direct intensity modulation is simple to

realize, higher performance is achieved by FM modulating the base band signal prior to intensity

modulation.

Laser diodes (LDs) are used in telecom, datacom and viedo communication applications

involving high speed and long hauls. All single mode optical fiber communication systems use Lasers

in the 1300 nm and 1550 nm windows. Lasers with very small line widths also facilitates realization

of wave length division multiplexing (WDM) for high density communication over a single fiber. The

inherent properties of Lds that make them suitable for such applications are, high coupled optical

intensity, small line-widths(less greater than 1 mw), high speed (several GHz) and high

linearity( over a specified region suitable for analog transmission). Special lasers also provide for

regeneration/amplification of optical signals within an optical fiber. These fibers are known as erbium

doped fiber amplifiers. LDs for communication applications are available in the wavelength regions

650 nm, 780 nm, 850 nm, 980 nm, 1300 nm and 1550 nm. Even though a variety of laser diode

constructions are available there are a number of common features in all of them. We have selected

a very simple device (650 nm/ 2.5 mW) to demonstrate the functions of a laser diode. Interested

students may refer to additional information from the books listed in appendix III.


PART-B EXPERIMENT NO: 2CHARACTERIZATION OF LASER DIODE


Specifications of a typical laser diode at 650 nm are summarized below.

SPECIFICATIONS OF THE LASER MODULE @ 25 C:

Symbol Parameter Typical Unit

* Po Cw o/p power 2.5 mW

*lop Operating current 30 mA

*Wp wave length at peak emission 650 nm

*MTTF mean time to failure 10000 Hrs

Monitor Photo Detector (MPD), Automatic Power Control and Automatic

Current Control modes of operation:

A Laser diode has a built in photo detector, which one can employ to monitor the optical

intensity of the laser at specified forward current. This device is also effectively utilized in designing

an optical negative feedback control loop, to stabilize the optical power of a laser in steep lasing

region. The electronic circuit scheme that employ the monitor photo diode to provide a negative

feedback for stabilization of optical power is known as the automatic power control alone to set

optical power then this mode is called the automatic current control mode (ACC). The disadvantage

of ACC scheme is that the optical power output may not stable at given current due to the fact that

small shifts in the lasing characteristics occur with temperature changes and aging. The

disadvantage of the APC is that the optical feedback loop may cause oscillations, if not designed

properly.



Fig. 2.1 Laser Diode trainer kit.

Po vs IF Experiment:

The schematic diagram for study of the LD Po as a function of LD forward current IF is shown

below and is self explanatory.

PROCEDUERE:

1. Connect the 2 meter PMMA FO cable (Cab 1) to TX unit of LT-2023 and couple the laser light

to the power meter (FOP in) on the Rx unit as shown select ACC mode of operation.

2. Set DMM 1 to the 2000mV range and on the Rx side connect to the terminals marked Po

(between Po1 and Po2) to it. Turn it on. The power meter is now ready for use. Po=

(Reading)/10 dBm.

3. Set DMM 2 to 2000mV range and connect it between Vo and Gnd on the TX unit (IF

=Vo/100), R1 =100Ohms.

4. Adjust the SET Po on the TX knob to the extreme anticlockwise position to reduce If to 0( i.e

Vo =0V) the power meter reading will normally be below -40dBm or out of range.

Note: There will be a negligible offset voltage.

5. Slowly turn the SET Po knob and clockwise to increase IF and Po. Note IF and PO readings.

Take closer readings prior to and above the laser threshold.

6. Plot the graph Po vs IF on a semi log graph sheet. Determine the slops prior to lasing and

after lasing. Record the laser threshold current graph shown.



Fig. 2.2 Setup for measurement of Po with respect to IF.

S.NO Vo(mV) IF=Vo/100(mA) Po(dBm) Po(mW)123456

INFERENCES:

From the above table it is seen that the laser optical o/p does not increase

appreciably for IF below threshold current Ith. Above Ith Po increases steeply Po is very

steep. The laser threshold may be determined from the graph or by recording closer

readings.

CRITICISM:

1. Light frequencies used in optical fiber communication systems are between ___ and

____Hz.

2. LASER means ______

3. SONET means _____

4. Subsonic frequencies are___ Hz

5. Cosmic rays ______Hz

6. Wave lengths ranging between 770nm and 106 nm are called____

7. Wavelengths ranging between 390nm and 770nm are called ____

8. Wavelengths ranging between 10nm and 390nm are called ____

9. What is Snells law?

10. Determine the light frequency for the following wavelengths

a. 670 nm

b. 7800Ao

c. 710nm

WORK SPACE




PART – B EXPERIMENT NO: 3

INTENSITY MODULATION OF LASER OUTPUT THROUGH OPTICAL FIBRE


Date:Pre-Lab:


2. Study the fundamental concepts of a Fiber Optics system.

Objective:

1. To study the Vin(ac) Vs Vout characteristics for fixed carrier Power Po and signal Frequency

Fo

2. To study the Vin max Vs Po characteristics for known distortion free Vout at fixed Fo.

Equipment required:

1. Laser TX unit.

2. Laser RX unit.

3. DMM (2 nos.)

4. CRO.

5. Patch cards.

6. Function generator.

7. PMMA FO cable.

8. Power supply.

CIRCUIT DIAGRAM:

Fig. 3.1 Laser Diode trainer kit



Theory: The Intensity Modulation /Demodulation system is realized using the LT-2023 TX Unit and

the LT-2023 Rx unit linked through an optical fibre. We use the 2- meter PMMA fibre cable. The laser

carrier power, Po is set by adjusting the SET P0 Knob in the middle laser region. Selection of

optimum carrier power is essential to minimize distortion. Limiting depth of modulation also ensures

distortion free Transmission. In the band width of the system in the present case is limited by the

Photo Detector. We may choose to operate in the ACC or APC mode to obtain Optical output

proportional to the modulating signal Vin.

An ideal Intensity modulation Transmission system will have the relationship Vout = G.Vin,

Where G is a factor dependent on LD conversion efficiency, Loss in the Optical Transmission path

and the Laser photo detector conversion efficiency. Distortion results from the LD being biased in

the nonlinear region. Band width is limited by the slowest device in the system; in this case it is

Photo Transistor. Speed can be increased by using a PIN diode, which is inherently a faster devise.

Procedure:

1. Connect one end of the PMMA FO cable to the Laser port on the TX unit. The other end is

first connected to FO PIN to set carrier power level of the laser. Then it is removed and given

to FO PT (Rx unit) to study the response of the IM system.

2. Set DMM to the 2000mV range. Connect it to P0. The Power meter is now ready for use. P0

= (Reading)/ 10 dBm.

3. On the TX unit connect Vin to a Function Generator (10 Hz to 500 kHz sine wave output,

10mV to 2ooomV p-p output. The black lead is GND. Give the function generator output to

CH 1, as shown.

Fig. 3.2 Setup for measurement of gain(G).



4. On the RX unit, connect Vout to CH2 of Dual Trace Oscilloscope. Connect the black lead to

GND.

5. Plug the AC mains for both systems.

6. With the PMMA FO cable connected to the Power meter, adjust the SET P0 knob to set the

Optical carrier power meter and connect to FO PT.

7. Set signal frequency and amplitude to 2 kHz and 100mV respectively. Observe the

transmitted and received signals on the Oscilloscope. Set Rin suitably to get Vout = Vin or a

known Gain or minimum Gain. The system Gain is now set.

8. Vary Vin in suitable values from 10mV to 200mVP-P and note the values of Vout. Tabulate

and plot a graph Vout Vs Vin.

Table of Readings:

S.No Vin(mVp-p) Vout (mV p-p) G=Vo/Vin

9. Set signal frequency to 2kHz and P0 to -25.0 dBm. Disconnect Vin before Po measurement.

Set Vin to its max value for distortion free Vout. Note the values of Vin and Vout. Repeat this

for other values of P0 and record change in gain if any. We may additionally observe the

wave forms in the Oscilloscope dc coupled position too. You may also compare the ACC and

the APC modes in the case of IM.

Table of Readings:

S.No Po(dBm) Vin max(mV p-p) Vout(mVp-p) G=Vo/Vin

1.

2.

3.



INFERENCE:

CRITICISM:

1. Draw the simplified block diagram of an optical fiber communications link.

2. What is the function of an optical regenerator?

3. Define intensity modulation .

4. Know the history of optical fiber communication.

5. Determine the optical power received in dBm and Watts for a 20 Km optical fiber link with

the following parameters.

LED output power of 30 mW.

Four 5 Km sections of optical cable each with a loss of 0.5dB per Km

Three cable – cable connectors with a loss of 2dB each

No cable splices

Light source- to – fiber interface loss of 1.9dB

Fiber – Light detector loss of 2.1dB

No losses due to cable bends



WORK SPACE


PART-B EXPERIMENT NO: 4DETERMINATION OF NUMERICAL APERTURE OF GIVEN

OPTICAL FIBRES


Date:Pre-Lab:


2. Study about velocity of propagation, Refraction, refractive index, Critical angle,

acceptance angle, acceptance cone and NA

Objective:The aim of the experiment is to determine the Numerical Aperture of the given Optical Fiber

(either glass fiber or plastic fiber).For glass fibers the NA may vary between 0.1 to 0.25 and for

plastic fiber it may be between 0.4 to 0.5.

Equipment required:

Laser Transmitter and Optical fibers of Different lengths and Accessories.

Theory: Numerical aperture of any optical system is a measure of how much light can be collected by

the optical system. It’s the product of the refractive index of the incident medium and the sine if the

maximum ray angle.

NA = ni.sinθmax. ni = 1 for air.

For a step index fiber, as in the present case, the Numerical aperture is given by

N = (ncore² -ncladding²)½.

For very small differences in refractive indices the equation is

N = ncore (2∆) ½ where ∆ is the fractional difference in refractive indices.

Fig 4.1 The schematic diagram of Optical Fiber


θ


The experimenter may refer to the specifications of the PMMA fiber given in Appendix 1 and

record the manufacturer’s n (cladding) and n (core) and ө.

The schematic diagram is shown above.

Fig. 4.2 Measurement setup for finding the NA of given FOC

PROCEDURE:

1. Connect the end of the PMMA FO Cable to Po LT-2023 TX Unit and the other

end to the NA Jig, as shown.

2. Plug the AC Mains, Light should appear at the end of the fiber on the Na Jig.

Turn the SET Po knob clock wise to set to maximum Po. The light intensity should

increase.

3. Hold the white scale-cum screen, provided in the Kit vertically at a distance

of 15 mm (L) from the end view the red spot on the screen. A dark room will facilitate

good contrast. Position the screen-cum scale to measure the diameter (W) of the spot.

Choose the largest diameter.

4. Compute NA from the formula NA = W/ (4L²+W²)½. Tabulate the readings

and repeat the experiment for 10mm 20mm 25 mm distance.

TABLE OF READINGS

S.No Length of the given cable

W LNa=W/(4L2+W2)1/2

θa

1

2

3

4



Fig. 4.3 Diagram for measuring the parameter W

INFERENCES: The Numerical aperture as recorded in the manufacturer’s data sheet is 0.5 typically.

The value measured here is 0.437. The lower reading recorded is mainly due to the fiber being

under filled. The acceptance angle is given by 2Өmax. The value of 52 degrees recorded in the

experiment is close to the range 0f 55-60 degrees. The lower reading is again due to the fiber being

under filled.

The procedure may be repeated for cable 2 too. Since the power from the smaller core

fibers will not be intents, we may have to carryout the experiment in a dark room.

CRITICISM:

1. Define velocity of propagation.

2. Define refraction.

3. Define refractive index.

4. Define snells law.

5. Define critical angle.

6. Define acceptance angle.

7. Define acceptance cone.

8. Define Numerical Aperture.

9. Differentiate between single mode and multi mode.

10. A multi mode step index fiber with a core diameter of 50 micro M, a core refractive

index of 1.6, a cladding refractive index of 1.584, and a wavelength of 1300nm has

approximately___ possible modes.


2.4 CM

1.9CM

1.4 CM

0.9CM


WORK SPACE



Date:

Pre-Lab:1. Study the optical communication kit.

2. Study about optical fiber configurations, optical fiber classifications, losses in optical fiber

cables.

Objective:

The aim of the experiment is to study the various types of losses that occur in optical fibers

and measure the loss in dB of optical patch cords individually and also connected in tandem using an

in-line adaptor.

Equipment required:1. Laser transmitter and receiver Optical fiber2. connector and Accessories

Theory:

Attenuation in an optical fiber is a result of number of effects. This aspect is well covered in

books referred. We will confine our study to attenuation in a fiber due to macro bending and

estimate the losses in the patch cords.

The loss as a function of the length of the fiber is not measurable here as the lengths of

fibers under consideration are too short. Fiber loss variations with wavelength for the PMMA fiber

under consideration are shown in Appendix 1. The details of glass graded index multimode fibers are

given in Appendix 1.

The optical power at a distance L in an optical fiber is given by

PL = P0 10*(αL/10). Where P0 is the launched power and α is the attenuation coefficient in dB

per unit length. The typical attenuation coefficient value for the PMMA fiber under consideration here

is 0.3 dB per meter for light at a wave length of 660 nm. For the GI fibers it is of the order of 3 to 4

db per km at 850 nm.

Loss in fibers expressed in dB is given by -10 log (Po/Pf) where, Po is the launched power

and Pf is power at the far end of the fiber. Typical losses at connector junctions may vary from 0.3 to

0.8 dB.

The loss equation for a simple fiber optic link is given as:

Pin(in dB) – Pout(in dB) = Lj1+Lj2+LFIB2+Lj3(dB), where Lj1 is the loss at LED connector junction,

Lj2 is the insertion loss at a splice or in-line adaptor, LFIB2 is the loss at cable 2 and Lj3 is the loss

at the connector detector junction.


PART-B EXPERIMENT NO: 5

MEASUREMENT OF LOSSES FOR ANALOG OPTICAL LINK


Losses in fibers also occur at fiber –fiber joints or splices due to axial displacement,

angular displacement, separation, mismatch of cores diameters, numerical apertures, improper

cleaving at the ends.

The patch cords designed for the experiment are as follows:

Cable 1: 2 – meter PMMA SI/MM (BLACK JACKET)

Cable-2: 2- meter 62.5/ 125 GI/MM (ORANGE JACKET)

PROCEDURE:

1. On the RX unit set the DMM to the 2000mV range. Connect it to the Po port of the RX unit.

2. Connect FO cable 1 between Po and Pin as shown. Set APC Mode.

3. Adjust the SET Po knob to set PO to a suitable value, say -12.0 dBm (the DMM will read

-150 mV). Note this as Po1.

4. Next repeat measurements with cable 2and note reading as Po2.

5. Use the In – Line SMA adaptor and connect the cables in series as shown and note down the

readings Po3.

Fig. 5.1 Setup for measurement of output power

TABLE:

S.NO CABLE LENGTH Optical power output dBm

1

2

3



INFERENCES:

Power coupled into a fiber with in the acceptance angle proportional to core cross

sectional area. The power coupled into a 1000 micron core PMMA fiber (cable 1) as compared with

the 62.5 micron core GI MM fiber (cable 2) will be 250 times greater or 24 dB higher. The measured

readings match the expected value.

CRITICISM:

1. Define absorption loss.

2. Define material, or Rayleigh, Scattering losses.

3. Define chromatic or wavelength dispersion.

4. Define radiation losses.

5. Define modal dispersion.

6. Define coupling losses.

7. For a 300m optical fiber cable with a BLP ( Band width length product ) of 600MHz –Km

,determine the band width.

8. Define pulse spreading.

9. For an optical fiber 10Km long with a pulse spreading constant of 5ns/Km determine the

maximum digital transmission rates for

a. Return to Zero(RZ)

b. NRZ transmissions

10. Mention the typical loss of an optical fiber cable.



WORK SPACE



PART-C

EXPERIMENTS BEYOND THE SYLLABUS:

1. Measurement of gain of a wave guide horn antenna

2. Measurement of dielectric constant of a homogeneous material



Date:Pre-Lab:

1. Study the microwave test bench.

2. Study about Gain, Directivity, and Radiation pattern of Antennas.

Objective:

To measure the Gain of a WG Horn Antenna.

Equipment required: Gunn power supply, Gunn oscillator, PIN Modulator, Frequency Meter,

Isolator, Variable Attenuator, Detector Mount, Two Horn Antennas, Turn table, VSWR Meter and

accessories.

Theory:

If a Transmission line carrying EM energy is left open at one end, there will be radiation from

this end. In case of rectangular waveguide this antenna presents a mismatch of about 2:1 and it

radiates in many directions. The match will improve if the open waveguide is a Horn shape.

Antenna measurements are mostly made with unknown antenna as receiver. One method of

measuring gain of an unknown antenna is to use two identical antennas, one as transmitter and the

other as receiver from the following formula the gain can be calculated

PR = (Pt G1 G2 λ 2) / (4∏ S) 2

Where Pt = Transmitted power

Pr = Received power

G1, G2 =Gains of transmitting and receiving antennas

λ = Free – space wavelength

S = Distance between the two antennae

If both transmitting and receiving antennas are identical having gain G, then

Pr = (Pt G2 λ 2)/ (4∏ S) 2

G= (4∏ S/λ) √ (Pr/Pt)

Fig. 1.1 Setup for antenna gain measurement of gain(G)


PART-C EXPERIMENT NO: 1

MEASUREMENT OF GAIN OF A WAVE GUIDE HORN ANTENNA

DETECTOR MOUNT

VSWR METER

GUNN POWER SUPPLY

GUNN OSCILLATO

RISOLATO

R

PIN MODULATO

R

FREQUENCY

METER

VARIABLE ATTENUAT

OR


Procedure:

1. Setup the equipments as shown above. Both horns should be in line.

2. Keep the range dB switch of VSWR meter at 50 dB position with gain control full.

3. Energize the Gunn oscillator for maximum output at desired frequency.

4. Obtain full scale deflection in VSWR meter with variable attenuator.

5. Replace the transmitting horn by detector mount and change the appropriate range dB

position to get the deflection on scale (do not touch the gain control knob). Note and record

the range dB position and deflection of VSWR meter

6. Calculate the difference in dB between the power measured in step 4 and 5.

Example:

Suppose that a deflection of 5 dB on 20 dB range position was obtained in step 5, the

difference between 4 and 5 is 50 – (20 + 5) = 25 dB convert the dB into ratio. For the above

example it will come out to be 316 which will be Pt/Pr

Calculate gain by the following formula:

G= (4∏ S/λ) √ (Pr/Pt)

In our above example suppose the operating frequency is 9GHZ and distance between antennas is

150 CM.

7. Covert G into dB in above example

G in dB = 10 log10 318 = 15dB

8. The same setup can be used for other frequency of operation.

Observation & Calculations:

Result: Gain of the given antenna is found to be ________ dB.



CRITICISM:

1. Define an Antenna.

2. Define Gain of an Antenna.

3. Mention different type of microwave antennas.

4. What do you understand by RADIATION PATTERN of an antenna.

5. What is FRIIS TRANSMISSION equation?

6. Differentiate between Gain and Directivity of an antenna.

7. What are look angles?

8. Define LOS.

9. Define Beam width of an antenna.

10. Differentiate between Beam width and Bandwidth of an antenna.



WORK SPACE



Date:

Pre-Lab:

1. Study the microwave test bench.

2. Study about different materials like TFG, Alumina and etc.

Objective: To determine the Dielectric Constant of a Homogeneous Material.

Equipment required: Klystron power supply, Klystron oscillator, Frequency Meter, Isolator,

Variable Attenuator, Detector Mount, Waveguide Containing sample material.

Theory:

Refer Maxwell equation

x H =J + ðD/ðt --------( 1 )

x H = σE +jωεE ---------(2)

Where ε = (Real) Dielectric constant

The equation 2 can be rewritten as

x H = jω(ε-j σ/ω)E

Where ε* = ε -j σ/ω , is a complex Dielectric constant

The above equation can also be written as

ε* = ε0 (ε' -j ε")

Where ε"= σ/ω ε0 and ε' = ε/ ε0

It is usual practice to employ normalized complex dielectric constant

ε r= ε*/ ε0 = ε' -j ε"

In the above terms ε” is called loss factor and ε' is associated with ability of material to store

electric energy.

It is also useful to write the relative dielectric constant as ε r= ε'(1- j tan δ)

where Tan δ is referred as loss tangent.


PART-C EXPERIMENT NO: 2MEASUREMENT OF DIELECTRIC CONSTANT OF A HOMOGENEOUS

MATERIAL


D

Fig. 2.1 Setup for measuring dielectric constant

Procedure:

1. With no sample in the short circuited line find position of voltage minima Dr with respect to

an arbitrarily chosen reference, with the help of a slotted section with detector probe.

2. Measure the guide wave length λg by measuring the distance between two adjacent minima

in slotted line.

3. Remove short circuit, insert a sample and replace the short circuit in such a manner that it

touches the end of the sample.

4. Measure D, the position of minima in slotted line w.r.t the same reference as in step2.

5. Measure VSWR in the slotted line.

6. Repeat steps 1 to 6 with sample having different lengths.

Lossless Dielectric sample

1. Compute propagation constant

βg = 2∏/λg

2. Compute K= Tan [ βg( lE +DR – D)]/ βglE

Where lE =length of the sample

3. Slove transcendental equation for X

K=Tan X/X

4. The dielectric constant is given by

ε' = [(a/∏)2 (X/lE )2 +1]/ [(2a/λg)2 +1]

where a= width of the waveguide

λg= guide wavelength


WG containing sample

KLYSTRON POWER SUPPLY

VADETEC

ISOLATOR METER

TOR MOUNT

R

KLYSTRON OSCILLATOR

FREQUENCY METER

VARIABLE ATTENUATOR

SAMPLE

DETECTOR

Short Circuit


Observation and calculations:

Result:

CRITICISM:

1. Define dielectric loss tangent.

2. What do you mean by lossy dielectric?

3. The relative permittivity and loss tangent of POLYSTYRENE material is ____ and _____.

4. YIG material is used as _____.

5. Define Curie temperature.



WORK SPACE


44575327-Mwoc-Final-Lab-Manual-28-08-2010

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