EC Department SUBJECT NAME: Microwave Engineering … · Klystron Power Supply: Klystron Power...

EC Department SUBJECT NAME: Microwave Engineering

SUBJECT CODE: 2171001

B.E. 7th

SEMESTER

List of Practicals

Sr

No.

Name of Practical

1 Introduction to various components of microwave workbench and

measuring equipment.

2 To study Gunn diode V-I characteristics.

3 To study about characteristics of the Reflex Klystron Tube and to

determine its electronic range.

4 To determine the frequency and wavelength in a rectangular waveguide

working on TE10 mode.

5 To determine the standing wave ratio and reflection co-efficient.

6 To measure an unknown impedance using Smith chart.

7 To measure coupling factor, insertion loss and directivity of a Directional

coupler.

8 To study power division measurement in a Magic Tee.

9 To study measurement of vswr, insertion loss, isolation of Isolator and

Circulator.

10 To study Fixed and Variable attenuator.

EXPERIMENT: 1

AIM: Introduction to various components of microwave workbench and measuring

equipment.

THEORY:

MICROWAVE TEST BENCH:

Microwave Test Benches are precision made microwave systems, which use

standard type rectangular wave-guide components to illustrate the essential elements

of this field for study.

The equipment consist of:

1) A selection of wave-guide components

2) The power supply for the microwave source

3) A detector

4) A meter, which monitors the detector output

The components are explained below.

Klystron Power Supply:

Klystron Power supply is a state of art solid state regulated power supply for

operating low power klystron such as 2k25, 723 MB. Reflex Klystron uses only a

single cavity resonator and operates as an oscillator.

The various part included as electron gunn; Resonator, repeller and o/p coupling.

The reseller electrode is at a (-ve) potential and sends the partially bunched electrode

beam back to the resonator cavity. This provides a (+ve) feedback mechanism which

supports oscillation. If the voltage difference between resonator and repeller is V

and the distance is„d‟, the retardation experienced by the electron beam may be

obtained as

A= Force/Mass

= e/m

Gunn oscillator:

The Gunn Oscillator is based on negative differential conductivity effect in

bulk semi-conductor, which has two conductor bands minima separated at cathode

give rise to high field region, which travels towards anode. It disappears and another

domain is formed at cathode and starts moving towards anode and so on. The time

required for domain to travel from cathode to anode gives oscillation.

In a given oscillator, gunn diode is place in a resonant cavity. In this case the

oscillator frequency is determined by cavity dimension than by diode itself.

VSWR meter:

The meter indicates the signal level in propagation to the i/p which is

calibration directly in VSWR and db

Pin modulator:

Pin diode modulators are used to provide amplitude or pulse modulation in wide

range of microwave to study many applications.

These modulators uses PIN diode which is mounted across the waveguide

line with RF isolated DC bias lead passing to an external TNC(F).

Isolator:

This port circular may be converted into isolator by terminating one of its port

in\to momental load.

The isolator allows the waves to pass in one direction but stops them in

opposite direction.

Frequency meter:

It gives direct frequency on the dial provided These are recommended for used

Whenever quick determination of frequency and easy reading are desired.Direct

Reading frequency meters are used to measure the microwave frequency accurately.

There long scale length and numbered calibration marks provide high resolution

which is particularly useful when measuring frequency difference of small frequency

changes.

Variable attenuator Waveguide:

This is provided at least 20db of continuous variable attenuator. This Consist of

movable loosywave inside the section of a guide.

Magic Tee:

TEE consist of a section of waveguide with both series and shunt wave guide

arms mounted at the exact midpoint of main arm.

Fixed attenuator:

These are used for inserting a known attenuator to a waveguided. These of

attenuation to a waveguide.

These of a loosy inserted in a section flanged on the both ends.

H and E plane Tee:

Tee and series the type T junction and consist of three section of wave guide

joined together in order to divide and compare power levels.

E plane: The signal entering the first port of this junction will be equally divided of

second and third ports of the some magnitude but in \opposite phase

H Plane: the signal fed through the first port of h plane tee will be equally divided

in waveguide at 2nd

and 3rd

ports but in some phase.

Multiple Directional Coupler:

These are useful for sampling a port of microwave energy for monitoring

purpose and for measuring reflections and impedance.

Slotted Line:

Slotted section is used to measure various measuring parameter in microwave.

for example to determine VSWR, phase and impedances. These consist of a slot in

center of waveguide in which we can connect a probe and probe can be moved in

slot and position of probe can be measured by its Varnier scale. The travel of probe

carriage is more than three times of half wavelength.

Detector Mount:

The crystal detector can be used for the detection of microwave signal. At low level

of microwave power, the response of each detector approximates to square law

characteristics and may be used with a high gain selective amplifier having a square

law meter calibration.

EXPERIMENT: 2

AIM: To study Gunn diode V-I characteristics.

APPARATUS: Gunn Power Supply, Microwave Bench –Gunn oscillator, Gunn

diode, Isolators, Pin modulator, Variable attenuator (20 db),

Frequency meter, Slotted section, Detection mount, SWR meter.

THEORY: Gunn diodes are negative resistance devices which are normally used as

low power oscillator at microwave frequencies in transmitter and also as local

oscillator in receiver front ends.J.B. Gunn (1963) discovered microwave oscillation

in gallium arsenide (GaAs), Indium phosphide (InP) and Cadmium telluride

(CdTe).These are semiconductors having a closely spaced energy valley in the

conduction band as shown in figure for GaAs.

When dc voltage is applied across the materials, most of the electrons

will be locatedin the lower energy central valley T. At higher E-field, most of the

electrons will be transferred into the high energy satellite L & X valleys where the

effective electron mass is larger & hence electron mobility is lower than that in the

lower energy T valley.

Since the conduction conductivity is directly proportional to the mobility,

the conductivity & hence the current decreases with an increase in E-field or voltage

in an intermediate range, beyond a threshold value Vetch as shown in figure. This is

called transferred electron effect & the device is also called “Transfer Electron

Device”or “Gunn Diode”.

Thus, the material behaves as negative resistance device over a range of

applied voltages & can be used in Microwave oscillators.

The basic structure of a Gunn diode is shown in fig (a), which consists of

n-type GaAs semiconductor with regions of high doping (n+). Although there is no

junction this is called a diode with reference to the +ve end (anode), and negative

end (cathode) of the dc voltage applied across the device. If voltage or an electric

field at low level is applied to the GaAs, initially the current will increase with a rise

in the voltage. When diode voltage exceeds a certain threshold value Vth, a high

electric field is produced across the device where they become virtual immobile. If

the rate at which electrons are transferred is very high the current will decrease with

increase in voltage; resulting in an equivalent negative resistance effect. Since GaAs

is a poor conductor, Considerable heat is generated in the diode. The diode should be

well bounded into heat sink.

The electrical equivalent circuit of a gun diode is shown in figure where

Cj and -Rj are the diode capacitance and resistance respectively. Rs includes the total

resistance of a lead; ohmic contacts, and bulk resistance of the diode, Cp and Lp are

the package capacitance and inductance respectively. The negative resistance has a

value that typically lies in the range -5 to 20 ohms.Thegunn oscillator is based on –

ve differential conductivity effect in bulk semiconductor, which has two conduction

bands minima separated by an energy gap (greater than thermal agitation energies)A

disturbance at the cathode gives rise to high field region, which travels towards

anode & so on. The time required for domain to travel from Cathode to anode

(Transit time) gives oscillation frequency. In a gunn oscillator, Gunn diode is placed

in resonant cavity. In this case oscillator‟s frequency is determined by cavity

diminution than by diode itself.Althoughgunn oscillator can be amplitude modulated

with the bias voltage. We have used separate pin modulator through pin diode for

square wave modulation capability. A message of square wave modulation capacity

is modulation depth i.e. Output Ratio between on & off state.

PROCEDURE:

1. Set the component and equipment as shown in fig.

2. Initially set variable attenuation for max. Attenuation.

3. Keep control knob of gunn power supply as below: gunn bias knob: fully

anti clockwise.

4. Keep control knob of VSWR meter as below: meter switch: normal input

switch: low impedance, range db switch: 40 db, gunn control knob: fully

clock wise.

5. Set micrometer of the Gunn oscillator for required frequency of oscillation.

6. Switch on the Gunn power supply to voltage position.

7. Turn the meter switch of Gunn power supply to volt position.

8. Measure Gunn diode voltage corresponding to various current values

controlled by gunn bias knob through panel meter and meter switch, do not

exceed bias bolt above 10v.

OBSERVATION TABLE:

Sr.No CURRENT (Amp.) VOLTAGE (Volt)

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

CONCLUSION:

EXPERIMENT: 3

AIM: To study about characteristics of the Reflex Klystron Tube and to determine

its electronic range.

APPARATUS: Klystron power supply, Klystron tube with Klystron mount, Isolator

,Frequency meter, Variable attenuator, Detector mount, Wave guide

stand, VSWR meter, Oscilloscope

THEORY: The Reflex Klystron makes the use of velocity modulation to transform

a continuous electron beam into microwave power. Electron emitted from the

cathode are accelerated & passed through the positive resonator towards negative

reflector, which retards and finally, reflect the electrons and the electron turn back

through the resonator. Suppose an RF-field exists between the resonator the electron

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

changes in amplitude.

The accelerated electron leaves 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 through

the grids at such a time that electrons are slowed down by the voltage then energy

will be delivered to the resonator; and Klystron will oscillator.

The frequency is primarily determined by the dimensions of resonator

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.

PROCEDURE:

1. Connect the components and equipments as shown in figure.

2. Set the Variable Attenuator at the maximum position.

3. Set the mode switch of klystron power supply to CW position ,beam voltage

control knob to full anti-clock wise and reflector voltage control knob to

fully clock wise and the meter switch to OFF position.

4. Rotate the knob of Frequency meter at one side fully.

5. Put VSWR meter in 50 db att. and coarse find on mid direction and put in

low crystal impedance position.

Square wave operation:

1. Connect the equipments and components as shown in the fig.

2. Set Micrometer of variable attenuator around highest position.

3. Set Micrometer of variable attenuator around highest position.

4. Set the range switch of VSWR meter at 40db position, input selector switch

to crystal impedance position, meter switch to normal position.

5. Set Mod-selector switch to AM-MOD position. Beam voltage control knob

to fully anticlockwise position and meter switch to „OFF‟ position.

6. Switch „ON‟ the Klystron Power Supply, VSWR meter and cooling fan.

7. Change the meter switch of Klystron Power Supply to beam voltage knob

clockwise up to 300v.

8. Keep the AM-MOD amplitude knob and AM-FREQ knob at the mid-

position.

9. Rotate the reflector voltage knob to get the deflection in VSWR meter.

10. Rotate the AM-MOD amplitude knob to get the maximum output in VSWR

meter.

11. Maximize the deflection with & frequency control knob of AM-MOD.

12. If necessary, change the range switch of VSWR meter 50 db to 30 db if the

deflection in VSWR meter is out of scale or less than normal scale

respectively. Further the output can be also reduced by Variable Attenuator

for setting the output for any particular position.

13. Find the oscillation by frequency by Frequency Meter as described in the

earlier setup.

14. Connect oscilloscope in place at VSWR and see square wave across detector

mount.

Mode Study on Oscilloscope:

1. Set up component and equipments as shown in fig.

2. Keep position of variable attenuator at maximum position.

3. Set Mod selector switch to FM-MOD position with FM amplitude and FM

frequency knob at mid position. Keep beam voltage control knob fully

anticlockwise and reflector voltage knob to fully clockwise with meter

switch to „OFF” position.

4. Keep the time/division scale of oscilloscope around 100Hz frequency

measurement and volt/div to lower scale.

5. Switch On the klystron Power Supply and oscilloscope.

6. Change the meter switch of Klystron power supply to beam voltage position

and set beam voltage to 300V by beam voltage control knob.

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

reflector voltage anti-clockwise to get modes as shown in fig. As well as on

the oscilloscope. The horizontal axis represents voltage axis and vertical axis

reprents output power.

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

mode of Klystron tube can be seen on an oscilloscope.

CONCLUSION:

EXPERIMENT-4

AIM: To determine the frequency and wavelength in a rectangular waveguide

working on TE10 mode.

APPARATUS: Gunn Power Supply (NV101), Microwave bench -Gunn oscillator,

Gunn diode, Isolator, Pin modulator, Variable attenuator (20 db),

Frequency Meter, Slotted section, Detection mount, SWR Meter,

CRO, Cable.

THEORY: A Gunn diode oscillator can be designed by mounting the diode inside a

waveguide cavity formed by a short circuit termination at one end and by an iris at

other end as shown in figure. The diode is mounted at the centre perpendicular to the

broad wall where the electric field component is maximum under the dominant TE10

mode. The intrinsic frequency fo of oscillation depends on the electron drift velocity

Vd due to high field domain through the effective length L.

fo= Vd / L

For GaAs, Vd ≈ 107 cm/sec. Normally, the cavity is tuned to resonate at

the intrinsic frequency fo by adjusting the short position. A tuning screw is inserted

perpendicularly at the centre of the broad wall for fine frequency tuning.

The total resistive loading from the cavity and the external load should be

around 20 per cent higher than the Gunn device resistance –Rj so that the circuit

resistance - RLRj / (RL- Rj) will be negative. The cavity has an impedance

transforming property between the high impedance of the output waveguide and the

required low value for the Gunn diode. The Gunn diode is placed on a metal post.

The top of the post is insulated from the waveguide to form RF bypass capacitor and

dc bias voltage is applied to the post. The degree of coupling to the external

waveguide is adjusted by selecting the inductive iris dimension.

The power output of the Gunn diode oscillator is in the range of a few

watts for CW operation at biasing values 10V and 1A at 30- 40 GHz. A frequency

tuning range of nearly 2% can be achieved. For pulsed operation peak powers are

typically 100-200W. The power output of the Gunn diode is limited by the difficulty

of heat dissipation from the small chip. The advantages are small size, ruggedness

and low cost.

Mode represents in waveguides as either: TE m, n / TM m, n, Where, TE -

Transverse electric, TM- Transverse magnetic, m – Number of half wave length

variation in broader direction, n – Number of half wave length variation in shorter

direction.

λg/2 = (d1 – d2)

Here, d1 and d2 are the distances between two successive minima / maxima.

It is having lowest cut off frequency hence dominant mode.

For dominant TE10 mode in rectangular waveguide λo, λg and λc are related as

below:

For TE10 mode:

λc = 2a / m

Where, m =1 and „a‟ is broad dimension of waveguide, Where, λo – free space wave

length, λg – guide wave length, λc – cutoff wave length, Consider, C = f λ, Where,

C = 3 × 108 m/s is velocity of light, f = frequency

PROCEDURE:

1. Set up the components and equipment as shown in block diagram.

2. Set up the variable attenuator at maximum position.

3. Switch on the Gunn power supply, VSWR meter and cooling fan.

4. Adjust the voltage of power supply to get some deflection in VSWR meter.

5. Take the reading on Frequency meter at intersection of two horizontal and

one vertical red lines.

6. The value indicates the operating microwave frequency. At that frequency

the power becomes zero.

7. Take the reading from micrometer screw.

8. Turn the Gunn bias control knob to counter clockwise position.

9. Switch off the Gunn Power Supply.

OBSERVATION:

1) f =________________ 2) λ=________________

CALCULATION:

CONCLUSION:

EXPERIMENT: 5

AIM: To determine the standing wave ratio and reflection co-efficient.

APPARATUS: Gunn Power Supply (NV101), Microwave bench -Gunn oscillator,


Frequency Meter, Slotted section, Detection mount, Movable Short/

Termination or any unknown Load and BNC Cable, SWR Meter,

CRO, Cable, S-S Tuner.

THEORY: It is a ratio of maximum voltage along a transmission line is called

VSWR, as ratio of maximum to minimum current. SWR is measure of mismatch

between load and line.The electromagnetic field at any point of transmission line

may be considered as the sum of two traveling waves: the „Incident Wave‟

propagates from generator and the „Reflected Wave‟ propagates towards the

generator.

The Reflected Wave is set up by reflection of incident wave

fromdiscontinuity on the line or from the load impedance. The magnitude andphase

of reflected wave depends upon amplitude and phase of the reflectingimpedance.

The superposition of two traveling waves, gives rise to standing wave along with the

line. The maximum field strength is found where two waves are in phase and

minimum where the line adds in opposite phase. The distance between two

successive minimum (or maximum) is half the guide wavelength on the line. The

ratio of electrical field strength of reflected and incident wave is called reflection

between maximum and minimum field strength along the line.

Hence VSWR denoted by S is S= Emax / Emin = |E1|+|Er| / |E1|-|Er|, Where

E1 = Incident Voltage and Er = Reflected Voltage

Reflection Coefficient, ρ is ρ= Er / E1 = (Z-Z0) / (Z+Z0) Where, Z is the

impedance at a point on line, Z0 is characteristic Impedance.

The above equation gives following equation

| ρ| = S-1 / S+1

PROCEDURE:

1. Set up the equipment as shown in the block diagram.

2. Keep variable attenuator at maximum-position.

3. Keep the Control knob s of VSWR Meter as below:

Range : 40dB / 50 dB

Input Switch : Impedance Low

Meter Switch : Normal

Gain (Coarse-Fine) : Mid Position approx.

4. Keep the control knobs of Klystron power supply as below:

Mod-Switch : AM

Beam Voltage Knob : Fully Anticlockwise

Reflector Voltage Knob : Fully clockwise

AM frequency & amplitude

Knob : Mid Position

5. Switch ON the power supply, VSWR meter and cooling fan.

6. Turn the meter switch of klystron Power supply to beam. Voltage position

and set the beam voltage at 300V.

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

8. Tune the output by tuning the reflector voltage, amplitude and frequency of

AM modulation.

9. Tune for maximum deflection by tuning the plunger of Klystron Mount.

Then tune for maximum deflection by tuning the probe.

10. If necessary change the range dB-switch, variable attenuator position and

gain control knob to get deflection in the scale of VSWR Meter.

11. Move the probe along with slotted line, the deflection will change.

a. Measurement of low and medium VSWR:

o Move the probe along with slotted line to maximum deflection in VSWR

Meter.

o Adjust the VSWR Meter gain control knob or variable attenuator until meter

indicates1.0 on normal SWR scale (0-∞).

o Keep all the Control knobs as it is, move the probe to next minimum

position. Read the VSWR on scale and record it.

o Repeat the above step for change of S.S. Tuner probe & record the

corresponding SWR.

o If the VSWR is between 3.2 and 10, change the range dB switch to next

higher position and read the VSWR scale is 3 to 10.

b. Measurement of High VSWR (Double Minimum Method):

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

o Move the probe along with slotted line until minimum is indicated.

o Adjust the VSWR meter gain control knob and variable attenuator to obtain

a reading of 3 dB of normal dB scale (0 to 10 dB) of VSWR Meter.

o Move the probe to the left on slotted line until full-scale deflection is

obtained i.e. „0‟ dB on 0-10 dB normal dB scale. Note and record the probe

position on slotted line. Let it be S1.

o Repeat the step 3 and 4 and then move the probe right along with slotted line

until full scale deflection is obtained on 0-10 dB normal dB scale. Let it be

S2.

o Replace the S.S. Tuner and terminator by movable short.

o Measure the distance between two successive minima position on probe.

Twice this distance is wave guide length λg.

o Calculate SWR by following equation:

SWR = λg / π (S1- S2).

For different SWR, calculate the reflection coefficient.

12. Turn the Gunn bias control knob to counter clockwise position.

13. Switch off the Gunn Power Supply.

OBSERVATION:

1) VSWR(S) =_________

2) REFLECTION COEFFCIENT(ƍ) =_________

CONCLUSION:

EXPERIMENT: 6

AIM: To measure an unknown impedance using Smith chart.

APPARATUS: Gunn Power supply , Microwave bench, Gunn Diode, Gunn

Oscillator, Isolator, Variable Attenuator 20db, Frequency Meter,

Slotted Section, Tunable Probe, S.S Tuner, Movable

short\termination or any unknown load, VSWR Meter

THEORY: The impedance at any point of a transmission line can be in the form

R+jX. For comparison SWR (S) and Reflection Coefficient (R) can be calculated as:

R = (Z-Z0)/ (Z+Z0)

S = (1+|R|)/ (1-|R|)

Where, Z0=Characteristics impedance of w/g at operating frequency, Z=Load

impedance at any point.

The measure is performed in following way: The unknown device is

connected to the slotted line and the SWR=S0 and the position of one minima is

determined. Then unknown device is replaced by movable sort to the slotted line.

Two successive minima positions are noted. The twice of the difference between the

minima position will be guide-wave length. One of the minima is used as reference

for impedance measurement. Find the difference of reference minima and minima

position obtained for load. Let it be „d‟. Take a smith chart taking „1‟ as center; draw

a circle of radius equal to S0. Make a point on circumference of chart towards load

side at a distance equal to d/g. Join the center with this point.

Find the point where it cut the drawn circle. The coordinates of this point

will show the normalized impedance of load.

PROCEDURE:

1. Set up the equipment as shown in the block diagram.

2. Set the variable attenuator at the maximum position.

3. Keep the control knobs of VSWR meter as below: Range dB: 50dB position,

Meter switch: Normal position, Gain (Coarse and Fine): Mid position, Keep the

Control knobs of Gunn power supply as below: Mod switch: AM, Gunn Bias

knob: Fully Counter clockwise position

4. Switch „ON‟ the Gunn power supply, VSWR meter and cooling fan.

5. Slowly vary the Gunn Bias Voltage and set it to 10V ( approx).

6. If necessary, change the range dB switch.

7. Vary attenuator position & Control knob to get deflection in the scale of VSWR

meter.

8. After getting maximum deflection on VSWR meter replace detector mount to

S.S. tuner and V match terminal.

9. Tune the tunable probe for maximum deflection in VSWR meter.

10. Keep the depth of pin of S.S. tuner to around 3-4mm and lock it.

11. Move the probe along with the slotted line to get maximum deflection.

12. Adjust VSWR meter gain control knob and variable attenuator unit such that the

meter indicates 1.0 on the normal upper SWR scale.

13. Move the probe to next minima point note down the SWR=S0 on the scale. Also

note down the probe position, 14. Remove the S.S. tuner and Matched

Termination and place movable short at slotted line. The plunger of short should

be at zero.

15. Note down the position of two successive minimum positions. Let it be as d1

and d2. Hence g=2(d1-d2).

16. Calculate d/g.

17. Find out the normalization impedance as described in the theory section.

18. Repeat the same experiment for other frequency if required.

19. Turn the Gunn bias knob in counter clockwise direction.

20. Turn off the Gunn Power Supply.

OBSERVATION:

d=___________ S0=___________ d1=___________ d2=___________

g=2(d1-d2) = ___________

Unknown Impedance from Schmitt Chart (normalized) = ___________

CONCLUSION:

EXPERIMENT: 7

AIM: To measure coupling factor, insertion loss and directivity of a Directional

coupler.

APPARATUS: Gunn power Supply (NV101), Microwave bench - Gunn oscillator,


Frequency meter, Slotted section, Detection mount, Microwave

Power Meter, Directional Coupler, CRO, Connectors and cables as

required.

THEORY: A directional coupler is a device with which it is possible to measure the

incident and reflected wave separately online. It consists of two transmission line,

the main arm and auxiliary arm, electromagnetically coupled to each other. When

power is coupled at the input port P1, it gets split into 2 parts by the directional

coupler. Majority of power is obtained at port2 which is output power. The opening

of the main waveguide into the adjacent waveguide is through holes placed λ/4 apart

due to which they power is added in phase at the Forward Port (Port 3) and added

out of phase at the Backward Port (Port 4). However, any power obtained due to any

mismatch is terminated at port 4 by an internal terminator to avoid any reflection

from this port. When Directional coupler is fed from Port2, we obtain Backward

Power at Port 3 and Forward Power is terminated at Port 4.

Directional Coupler

Coupling (db) = 10 log10 [P1/P3] ,where port 2 is terminated

Isolation = 10 log10 [P1/P4], where P1 is matched.

With built-in termination and power is entering at port 1. The directivity of

the coupler is a measure of separation between incident and the reflected wave. It is

measured as the ratio of two power outputs from the auxiliary line when a given

amount of power is successively applied to each terminal of the main lines with the

port terminated by material loads.

Directivity 0(db) = Isolation – Coupling = 10 log10 [P3/P4]

Min line VSWR is SWR Measured looking into the main line input

terminal when the matched loads are placed at all other ports.

Auxiliary line VSWR is SWR measured in the auxiliary line looking into

the output terminal, when the matched loads are placed on other terminals.

Main line insertion loss is the attenuation introduced in transmission line

by insertion of coupler. It is defined as insertion loss.

Insertion Loss = 10 log10 [P1/P2], where power is entering at port 1

PROCEDURE:

Measurement of coupling, insertion loss and directivity:

1. Set up the equipments as shown in the block diagram below.

2. Klystron and gunn oscillator.

3. Energies the microwave source for particular frequency operation as

described operation of and Gunn Oscillator.

4. Remove the multi-hole directional coupler and connect the detector mount to

the frequency meter. Tune the detector for the maximum output.

1. Set any reference level of power on Microwave power meter with the help of

variable attenuator, gain control knob of Microwave power meter, and note

down the reading. (Reference level let it be P1).

2. Insert the directional coupler as shown in second fig. with detector to the

auxiliary port 3 and matched termination to port 2, without changing the

position of variable attenuator and gain control knob of Microwave power

meter.

3. Note down the reading on Microwave power meter on the scale with help of

range-db switch if required. (Let it be P3)

4. Calculate coupling factor, which will be P1-P3 in dB.

5. Now carefully disconnect the detector from the auxiliary port 3 and detector

to port 2 without disturbing the set-up.

6. Connect the matched termination to the auxiliary port 3 and detector to port

2 and measure the reading on Microwave power meter. Suppose it is P2.

7. Compute insertion loss P1-P2 in dB.

8. Connect the directional coupler in the reverse direction, i.e. port 2 to

frequency meter side, matched termination to port 1 and detector mount to

port 3, without disturbing the position of the variable attenuator and gain

control knob of Microwave power meter.

9. Repeat the same for other frequencies.

10. Turn the Gunn bias control knob to counter clock wise.

11. Switch off the Gunn power supply.

OBSERVATION:

1. Input Power at port 1, P1 =____________

2. Output Power at port 2, P2=____________



CALCULATION:

1) Coupling (dB) = 10log10 (P1/P4)

2) Isolation (dB) = 10log10 (P2/P3)

3) Directivity = Isolation (dB) - Coupling (dB) = 10log10 (P2/P1)

4) Insertion = 10log10 (P1/P2)

CONCLUSION:

EXPERIMENT: 8

AIM: To study power division measurement in a Magic Tee.

APPARATUS: Microwave source, Isolator, Variable attenuator, Frequency meter,

Slotted line, Tunable probe, H-plane Tee, E-plane Tee and Magic

Tee, Matched termination, Wave guide stand, Detector mount,

Microwave Power meter, Accessories.

THEORY:

Microwave T-junctions:

A T-junction is an intersection of three waveguides in the form of English

alphabet „T‟. There are several types of Tee junctions. The following Tee junctions

will be discussed.

1. H-plane Tee junction

2. E-plane Tee junction

3. Magic-T junction

H-plane Teejunction:

An H-plane Tee junction is formed by cutting a rectangular slot along the

width of a main waveguide and attaching another waveguide-the side arm-called the

H-arm as shown in Fig. The port1 and port2of the main waveguide are called

collinear ports and port3 is the H-arm or side arm. H-plane Tee is so called because

the axis of the side arm is parallel of the planes of the main transmission line. As all

three arms of H-plane Tee lie in the plane of magnetic field, the magnetic field

divides itself in to the arms. Therefore this is also called a current junction. When

power is fed to port 3, it gets divided equally in port 1 and port 2 and both the

powers are in same phase.

E-plane Tee:

A rectangular slot is cut along the broader dimension of a long waveguide

and a side arm is attached as shown in Fig. Port1 and port2 are the collinear arms and

port3 is the E-arm.

When TE10 mode is made to propagate into port3, the two outputs at

port1 and port2 will have a phase shift of 180 degree as shown in Fig. Since the

electric field lines change their direction when they come out of port1 and port2, it is

called an E-plane Tee. E-plane Tee is a voltage or series junction

symmetrical about the central arm. Hence any signals that is to be split or any two

signal that are to be combined will be fed from the E arm. The scattering matrix of

an E-plane Tee can be used to describe its properties. In general, the power out of

port3 (side or E arm) is proportional to the difference between instantaneous powers

entering from port1 and port2.Also, the effective value of the power leaving the E

arm is proportional to the phase difference between the powers entering ports 1 and

2.when powers entering the main arms (ports 1 and 2) are in phase opposition,

maximum energy comes out of port 3 or E arm.

Magic Tee:

Here rectangular slots are cut both along the width and breadth of a long

waveguide and side arms are attached as shown in Fig. Ports 1 and 2 are collinear

arms, port 3 is the H-arm, and port 4 is the E-arm. Such a device became necessary

because of the difficulty of obtaining a completely matched three port Tee junction.

This four port hybrid Tee junction combines the power dividing properties of both

H-plane Tee and E-plane Tee as shown in Fig and has the advantage of being

completely matched at all its port. When power is input at port 3, there is no power

at port 4 and vice versa i.e. it provides isolation between the ports 3 and 4.

PROCEDURE:

(A): For H-Plane Tee:

1. Connect the apparatus as per block diagram given below

2. Remove the tunable probe and H-Plane Tee from the slotted line and connect the

detector mount to slotted line.

3. Energize the microwave source for particular frequency of operation and tune the

detector mount for maximum output.

4. Measure the input power to the Tee by placing the Microwave Power meter. This

is input power to the tee and this is the input Port

5. Without disturbing the position of variable attenuator and gain control knob,

carefully place the H-plane Tee after slotted line.

6. Determine the two output powers using Microwave Power meter.

7. Move the Gunn Power bias knob in counter clockwise direction

8. Turn off the Gunn Power Supply

(B): For E-Plane Tee

1. Connect the apparatus as per block diagram given in above procedure

2. Remove the tunable probe and E-Plane Tee from the slotted line and connect

the detector mount to slotted line.

3. Energize the microwave source for particular frequency of operation and

tune the detector mount for maximum output.

4. Measure the input power to the Tee by placing the Microwave Power meter.

This is input power to the tee and this is the input Port


carefully place the E-plane Tee after slotted line.

6. Determine the two output powers using Microwave Power meter.



(C): For Magic Tee

1. Connect the apparatus as per block diagram given below

2. Remove the tunable probe and Magic Tee from the slotted line and connect

the detector mount to slotted line.

3. Energize the microwave source for particular frequency of operation and

tune the detector mount for maximum output.

4. Measure the input power to the Tee by placing the Microwave Power meter.

This is input power to the tee and this is the input Port


carefully place the Magic Tee after slotted line keeping H-arm connected to

slotted line, detector to E-arm and matched termination to arm 1 and 2. Note

down the reading of Microwave Power meter. Determine the isolation

between port 3 and port 4 as P3-P4 in dB.

6. The same experiment can be repeated for other ports also.

7. Repeat the above experiment for other frequency.



CONCLUSION:

Experiment No. 9

AIM: To study measurement of vswr, insertion loss, isolation of Isolator and

Circulator.

APPARATUS: Micro-wave source, Klystron power supply 5KPS610, Klystron

Tube 2K25, Klystron mount XM251, Isolator XI621, Frequency

meter XF710, Variable Attenuator XA520, Slotted line X565,

Detector Mount XD450, Wave guide stand XU535, BNC Cable,

VSWR Meter SW115, Cooling fan.

CIRCUIT:

THEORY:

A circulator is a ferrite device (ferrite is a class of materials with strange

magnetic properties) with usually three ports. Circulators are non-reciprocal. That is,

energy into port 1 predominantly exits port 2, energy into port 2 exits port 3, and

energy into port 3 exits port 1. In a reciprocal device the same fraction of energy that

flows from port 1 to port 2 would occur to energy flowing the opposite direction,

from port 2 to port 1.The selection of ports is arbitrary, and circulators can be made

to "circulate" either clockwise (CW) or counter-clockwise (CCW).

Fig (a)-Circulators

By terminating one port, a circulator becomes an isolator, which has the

property that energy flows on one direction only. This is an extremely useful device

for "isolating" components in a chain, so that bad VSWRs don't contribute to gain

ripple, or lead to instabilities (unwanted oscillations). An isolator is a non-reciprocal,

passive network.

Fig (b) Isolators

PROCEDURE:

1. Connect the apparatus as shown in the above figure.

2. Switch on the power supply.

3. Connect circulator and measure the output voltage on VSWR meter or CRO.

4. Give input to circulator from port 1 and measure voltages at port 2 and port -

3.

5. Repeat the above steps for port 2 and port 3.

6. Connect isolator and measure the output voltage from detector.

7. Give input to isolator at port 1, measure output at any one of another port

and terminate the rest left over port.

8. Repeat steps for port 2 and 3.

CONCLUSION:

EXPERIMENT: 10

AIM: To study Fixed and Variable attenuator.

APPARATUS: Microwave source, Isolator, freq. meter, Variable attenuator,

Slotted line, Tunable probe, Detector mount, Matched termination,

VSWR meter, Fixed and variable type attenuator.

THEORY:

The attenuator is two port bi directional devices which attenuates some

power when inserted into transmission line. Attenuation A(dB)=10log(base 10)

P1/P2, Where P1 is power absorbed or detected by load without the attenuator in the

line and P2 is power absorbed / detected by the load line with attenuation in the line.

The attenuation consists of a rectangular waveguide with resistive vane

inside it to absorb microwave power according to their positions with respect to side

wall of the waveguide. As electric field is maximum at centre in TE10 mode, the

attenuation will be maximum if the vane side wall, attenuation decreases in the fixed

attenuator. The vane position is fixed where as in variable attenuator; its position

can be changed by help of micrometer or by other methods.

PROCEDURE:

A) Input VSWR Measurement

1. Remove the tunable probe attenuator and matched termination form the

slotted section in the above set up.

2. Connect the detector mount to the slotted line and tune the detector mount

also for maximum deflection on VSWR meter.

3. Set any reference Level on the VSWR meter with the help of variable

attenuation and gain control knob of VSWR meter. Let it be P1.

4. Carefully disconnect the detector mount from the slotted line, without

disturbing any position on the set up. Place the test variable attenuator to the

slotted line and detector mount to other port of test variable attenuator.

5. Keep the micrometer reading of test variable attenuator to zero and record

the reading of VSWR meter. Let it be P2, then the insertion loss or test

attenuator will be P1-P2 dB.

6. For measurement of attenuation of step 4 of above measurement. Carefully

disconnect the detector mount from the slotted line without disturbing any

position obtained up to step 3.

7. Place the test attenuator to the slotted line and detector mount to the other

port of test attenuator.

8. Record the reading of VSWR meter.

9. Let it be P3. Then the attenuation value of fixed attenuator for particular

position or micro meter reading will be P1-P3 dB.

10. In case of variable attenuator, change the micro meter reading and record the

VSWR meter reading. Find out Attenuation value for different position of

microwave reading.

11. Now change the operating frequency and whole step should be repeated for

finding frequency sensitivity for fixed and variable attenuator.

CONCLUSION:

EC Department SUBJECT NAME: Microwave Engineering … · Klystron Power Supply: Klystron Power...

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