characteristics of the reflex klystron … study the characteristics of the reflex klystron tube and...

MICROWAVE & RADAR LAB MANUALS DEPARTMENT OF ECE, BRCM CET, BAHAL, HARYANA (INDIA)

To study the characteristics of the reflex Klystron tube and to determine its electronic tuning range.

Klystron Power Supply, Klystron Tube, Isolator, Frequency Meter, Variable Attenuator, DetectorMount, Waveguide Stand, VSWR Meter and BNC Cable.

The Reflex Klystron makes use of velocity modulation to transform a continuous electron beam intomicrowave power. Electron emitted from the cathode are accelerated and passed through the positiveresonator towards negative reflector, which retards and, finally, reflects the electron; and the electronturns back through the resonator. Suppose an hf-field exists between the resonator, the electrontravelling forward will be accelerated or retarded, as the voltage at the resonator changes inamplitude. The accelerated electrons leave the resonator at an increased velocity and the retardedelectrons leave at the reduced velocity. The electrons leaving the resonator will need different timeto return, due to change in velocities. As a result, returning electrons group together in bunches. Asthe electron bunches pass through resonator, they interact with voltage at resonator grids. If thebunches pass the grid at such time that the electrons are slowed down by the voltage, energy will bedelivered to the resonator; and Klystron will oscillate. Fig. P1 shows the schematic of a typicalKlystron tube. Fig. P2 shows the relationship between output power, frequency and reflector voltage.The frequency is primarily determined by the dimension of resonant cavity. Hence, by changing thevolume of resonator, mechanical tuning range ofKlystron is possible. Also, a small frequency changecan be obtained by adjusting the reflector voltage. This is called Electronic Tuning Range. The sameresult can be obtained, if the modulation voltage is appliedon the reflector voltage VR as shown in the Fig. P1.

CHARACTERISTICS OF THE REFLEX KLYSTRON TUBE

AIM

APPARATUS REQUIRED

THEORY


(a) Carrier Wave Operation1. Connect the components and equipments as shown in the Fig. P3.

2. Set the Variable Attenuator at the maximum position (a zero micrometer reading).3. Set the Mod-Switch of Klystron Power Supply to CW position, beam voltage control knob tofully anticlockwise and reflector voltage control knob to fully clockwise and the Meter Switch to‘OFF’position.4.Rotate the knob of frequency meter at one sidefully.5.Put the multimeter in dc microampere range of 250 microampere.6. ‘ON’ the Klystroiz Power Supply, VSWR Meter and Cooling Fan for the Klystron tube.7. Put the meter switch to beam voltage position and rotate the beam voltage knob clockwiseslowly upto 300 V meter reading, and observe beam current on the meter by changing meterswitch to beam current position. “The beam current should not increase more than 30 mA”8. Change the reflector voltage slowly and watch on the micro. Set the voltage for maximumdeflection in the meter. If no deflection is obtained, change the multimeter switch position to 50microampere.9. Tune the plunger of Klystron Mount for the maximum output.

PROCEDURE


10. Rotate the knob of frequency meter slowly and stop at that position, when there is less outputcurrent on multimeter. Read directly the frequency meter between two horizontal lines and verticalmarker. If micrometer type frequency meter is used, read the micrometer reading and find thefrequency from its calibration chart.11. Change the reflector voltages and read the current and frequency for each reflector voltage andplot the graph as shown in Fig. P2.

(b) Square Wave Operation

1. Connect the equipments and components as shown in Fig. P3.2. Set the variable attenuator to around zero position.3. Set the range switch of VSWR meter at 40 db position, input selector switch to crystalimpedance position, meter switch to normal position.4. Set Mod-Selector switch to AM-MOD position, beam voltage control knob fully anti-clockwisedirection, reflector voltage control knob to the maximum clockwise position and meter switch toOFFU position.5. ‘ON’ the Klystron Power Supply, VSWR meter and cooling fan.6. Change the meter switch of Klystron Power Supply to beam voltage position,and rotate the beamvoltage knob clockwise up to 300 V deflections in meter.7. Keep, the AM-MOD amplitude knob and AM-FRE knob at the mid- position.8. Rotate the reflector voltage knob anti-clockwise to get deflection in VSWR meter.9. Rotate the AM-MOD amplitude knob to get the maximum output in VSWR meter.10. Maximize the deflection with frequency control knob of AM-MOD.11. If necessary, change the range switch of VSWR meter to 30 db or 50 db if the deflection inVSWR meter is out of scale or less than normal scale respectively. Further, the output can also bereduced by Variable Attenuator for setting the output for any particular position.12. Find the oscillation frequency by Frequency Meter as described in the earlier set-up.13. Observe the square wave modulation of the Klystron on the CRO as shown in Fig. P4.


(c) Mode Study on Oscilloscope1. Set up the components and equipments as shown in Fig. P3.2. Keep position of variable attenuator at ten positions.3. Set Mod selector switch to FM-MOD position with FM amplitude and FM frequency knob atmid position, keep beam voltage control knob fully anti-clockwise and reflector voltage knob tofully clockwise with meter switch to ‘OFF’ position.4. Keep the time/div. scale of oscilloscope around 100 Hz frequency measurement and volt./div. tolower scale.5. ‘ON’ the Klystron Power Supply and Oscilloscope.6. Change the meter switch of Klystron Power Supply to Beam Voltage position and set beamvoltage to 300 V 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 shownin Fig. P3 on the oscilloscope. The horizontal axis representsreflector voltage axis, and vertical axis represents output power.

8. By changing the reflector voltage and amplitude of FM modulation, any mode of Klystron tubecan be seen on Oscilloscope.

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1.klystron power supply should be constant.

2.BNC cable should be connected properly.

3.VSWR meter readings should be taken carefully.

RESULT

PRECAUTION


To determine the frequency and wave length in a rectangular waveguide working on TE10 mode.

Klystron tube, Klystron Power Supply, Klystron Mount, Isolator, Frequency Meter, VariableAttenuator, Slotted Section, Tunable Probe, VSWR Meter, Waveguide Stand, MovableShort/Matched Termination.

For dominant TE10 mode in rectangular waveguide λ○, λg and λc are related as below

where λ○= free space wavelengthλg = guide wavelengthλc = cutoff wavelengthFor TE10 mode, λc = 2a where a is broad dimension of waveguide.The following relationship can be proved

C =fλ

where c is velocity of light and f is frequency.

1. Set up the components and equipments as shown in Fig. P5.

PROCEDURE

THEORY

TO DETERMINE THE FREQUENCY AND WAVE LENGTH

AIMREQUIRED

APPARATUSREQUIRED


Fig. P5. Set up for frequency and wave-length measurement.

2. Set the variable attenuator at maximum position.3. Keep the control knobs of VSWR meter as below:

Range db — 50 db positionInput Switch — Crystal low ImpedanceMeter Switch — Normal positionGain (coarse and fine) — Mid position

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

Meter Switch ‘OFF’ Mod-Switch — AMBeam Voltage Knob — Fully anti-clockwiseReflector Votlage — Fully clockwise

AM-Amplitude Knob — Around fully clockwiseAM-Frequency Knob — Around Mid position

5. ‘ON’ the Klystron Power Supply, VSWR Meter and Cooling Fan.6. Turn the meter switch of Power Supply to beam voltage position

and set beam voltage at 300 V with the help of beam voltage knob.7. Adjust the reflector voltage to get some deflection in VSWR Meter.8. Maximize the deflection with AM amplitude and frequency control knob of powersupply.9. Tune the plunger of Klystron Mount for maximum deflection.10. Tune the reflector voltage knob for maximum deflection.11. Tune the probe for maximum deflection in VSWR Meter.12. Tune the frequency meter knob to get the ‘dip’ on the VSWR scale

and note down the frequency directly from frequency meter.13. Replace the Termination with movable short, and detune the frequency meter.14. Move probe alongwith the slotted line, the deflection in VSWR meter will vary. Move the probeto a minimum deflection position, to get accurate reading, it is necessary to increase the VSWRmeter range db switch to higher position. Note and recordthe probe position.15. Move the probe to next minimum position and record the probe position again.16. Calculate the guide wavelength as twice the distance between two successive minimum positions


obtained as above.17. Measure the waveguide inner broard dimension ‘a’ which will be around 22.86 mm for X-band.18. Calculate the frequency by following equation:

where c = 3 x 108 meter/sec., i.e., velocity of light.19. Veñ with frequency obtained by frequency meter.20. Above experiment can be verified at different frequencies.

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ResultRESULT

PRECAUTION


To determine the standing-wave-ratio and reflection coefficient.

Klystron tube, Klystron Power Supply, VSWR Meter, Klystron Mount, Isolator, Frequency Meter,Variable attenuator, Slotted line, Tunable probe, Waveguide Stand, Movable Short/Termination orany unknown load and BNC Cable, S-S Tuner.

The electromagnetic field at any point of transmission line, may be considered as the sum of twotravelling waves: the ‘Incident Wave’ propagates from generator and the reflected wave propagatestoward the generator. The reflected wave is set up by reflection of incident wave from adiscontinuity on the line or from the load impedance. The magnitude and phase of reflected wavedepends upon amplitude and phase of the reflecting impedance. The presence of two travellingwaves, gives rise to standing wave along with the line. The maximum field strength is found wheretwo waves are in phase and minimum where the two waves add in opposite phase. The distancebetween two successive minimum (or maximum) is half the guide wave-length on the line. The ratioof electrical field strength of reflected and incident wave is called reflection coefficient.The voltage standing wave ratio (VSWR) is defined as ratio between maximum and minimum fieldstrength along the line.

where Z is the impedance at a point on line, Z0 is characteristic impedance.

The above equation gives following equation:

1. Set up the equipment as shown in the Fig.P6.

STANDING WAVE RATIO AND REFLECTION COEFFICIENT

AIMREQUIRED

APPRATUS RREQUIRED

THEORY

PROCEDURE


2. Keep variable attenuator at maximum position.3. Keep the Control knobs of VSWR meter as below:

Range db — 40 db/50 dbInput Switch — Impedance lowMeter Switch — NormalGain (Coarse-fine) — Mid position approximately

4. Keep the control knobs of Klystron Power Supply as below:Meter Switch — ‘OFF’Mod Switch — ‘AM’Beam Voltage Knob — Fully anti-clockwiseReflector Voltage Knob — Fully clockwise

AM Frequency and amplitude knob — Mid position5. ‘ON’ the Klystron 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 300 V.7. Rotate the reflector 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. Also 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 VSWR1. Move the probe along with slotted line to get maximum deflection

in VSWR Meter. (Fig. P7).2. Adjust the VSWR meter gain control knob or variable attenuator

untill the meter indicates 1.0 on normal SWR Scale (0-OQ).3. Keep all the control knob as it is, move the probe to next

minimum position. Read the VSWR on scale and record it.4. Repeat the above step for change of S-S. Tuner probe depth and

record the corresponding SWR.5. If the VSWR is between 3.2 and 10, change the range dB switch

to next higher position and read the VSWR on second VSWRscale is 3 to 10.


(b) Measurement of High VSWR (Double Minimum Method)1. Set the depth of S-S. Tuner slightly more for maximum VSWR.2. Move the probe along with Slotted line untill a minimum is indicated.

3. Adjust the VSWR meter gain control knob and variable attenuator to obtain a reading of 3 db ofnormal dB of VSWR Meter.4. Move the probe to the left on slotted line untill full scale deflection is obtained, i.e., 0 db on 0-10db scale. Note and record the probe position on slotted line. Let if be d1. (Fig. P8).5. Repeat the step 3 and 4 and then move the probe right along with slotted line untill full scaledeflection is obtained on 0-10 db normal db scale. Let it be d2.6.Replace the S-S.Tuner and terminator by movable short.7. Measure the distance between two successive minima position of probe. Twice this distance isguide wave length λg.8. Compute SWR by following equation:



3.VSWR meter readings should be taken

PRECAUTION

RESULT


To measure an unknown Impedance with smith chart.

Klystron Tube, Klystron Power Supply, Klystron Mount, Isolator, Frequency Meter, VariableAttenuator, Slotted Line, Probe, VSWR Meter, Waveguide Stand, S-S. Tuner, MovableShortlTermination etc.

The impedance at any point of a transmission line can be written in the form R+jx.For comparison SWR can be calculated as

Where p = reflection coefficient =

Z is the impedance at any point. The measurement is performed in following way:

The unknown device is connected to the slotted line and the SWR = So and position of one minimais determined. Then unknown device is replaced by movable short to the slotted line. Twosuccessive minima positions are noted. The twice of the difference between minima position will beguide-wave length. One of the minima is used as reference for Impedance measurement. Find thedifference of reference minima and minima position obtained from unknown load. Let it be d. Take asmith chart, taking ‘1’ as centre; draw a circle of radius equal to S0. Mark a point on circumferenceof chart towards load side at a distance equal to λg . Join the centre with this point. Find the pointwhere it cuts the drawn circle. The co-ordination of this point will show the normalized impedanceof load.

TO MEASURE AN UNKNOWN IMPEDANCE WITH SMITH CHART.

AIM

APPRATUS REQUIRED

THEORY

PROCEDURE


1. Set up the equipments as shown in the Fig. P9.2. Set the variable attenuator at maximum position.

Fig P9. Impedance measurement

3. Keep the control knobs of VSWR meter as below:Range db — 50 db positionInput Switch — Crystal low impedanceMeter Switch — Normal positionGain (Coarse and fine) — Mid position.

4. Keep the control knobs of Klystron power supply as below:Meter Switch — ‘OFF’ModSwitch — AMBeam Voltage Knob — Fully anti-clockwiseReflector Voltage — Fully clockwise

AM-Amplitude — Around fully clockwiseAM-Frequency Knob — Around mid position

5. ‘ON’ the Klystron power supply, VSWR meter and cooling fan.6. Turn the meter switch of power supply to beam voltage position

and set beam voltage at 300 V with help of beam voltage knob.7. Adjust the reflector voltage to get some deflection in VSWR meter.8. Maximize the deflection with AM amplitude and frequency

control knob of power supply.9. Tune the plunger of Klystron Mount for maximum deflection.10. Tune the reflector voltage knob for maximum deflection.11. Tune the robe for maximum deflection in VSWR meter.12. Tune the frequency meter knob to get a dip on the VSWR scale,

and note down the frequency directly from frequency meter.13. Keep the depth of pin of S-S. Tuner to around 3-4 mm and lock it.14. Move the probe along with slotted line to get maximum deflection.15. Adjust VSWR meter gain control knob and variable attenuator

until, the meter indicates 1.0 on the normal upper SWR scale.16. Move the probe to next minima point, note down the SWR = S0 on the scale, also, note downthe probe position, let be d. (Fig. PlO).


17. Remove the S-S. Tuner and Matched Termination and place movable short at slotted line. Theplunger of short should be at zero.18. Note the position of two successive minima position. Let it be asd1 and d2. Hence λg = 2 (d1- d2).

19. Calculate d/λg.20. Find out the normalized impedance as described in the theory section.21. Repeat the same experiment for other frequency if required.




PRECAUTION

RESULT


To study the following characteristic of Gunn Diode

1. V-I Characteristic.

2. Output power and frequency as a function of voltage.

3. Square wave modulation through PIN diode.

Gunn Oscillator, Gunn Power Supply, PIN Modulator, Isolator, Frequency Meter, Variable Attenuator,Detector Mount, Waveguide Stands, SWR Meter, Cables and accessories.

The Gunn Oscillator is based on negative differential conductivity effect in bulk semi-conductorswhich has two conduction bands minima separated by an energy gap (greater than thermalagitational energies). A disturbance at the cathode gives rise to high field region which travelstowards the anode when this high field domain reaches the anode, it disappears and another domainis formed at the cathode and starts a moving towards anode and so on. The time required for domainto travel from cathode to anode (transit time) gives oscillation frequency.

In a Gunn Oscillator, the Gunn diode is placed in-a resonant cavity. In this case the Oscillationfrequency is determined by cavity dimension than by diode itself. Although Gunn oscillator can beamplitude-modulated with the bias voltage. We have used seperate PIN modulator through PINdiode for square wave modulation. A measure of the square wave modulation capability is themodulation depth, i.e., the output ratio between ‘ON’ and ‘OFF’ state.

1. Set the components and equipments as shown in the Fig. P11.

2. Initially set the variable attenuator for maximum attenuation

3. Keep the control knob of Gunn Power Supply as below:

Meter Switch — ‘OFF’,

CHARACTERISTIC OF GUNN DIODE

AIM

APPARATUS REQUIRED

THEORY

PROCEDURE


Gunn bias Knob — Fully anti-clockwise

Pin bias Knob — Fully anti-clockwisePin Mod frequency — Any position

4. Keep the control knob of VSWR meter as below:Meter Switch — NormalInput Switch — Low impedanceRange db Switch — 40 db

Gain control knob — Fully clockwise5. Set the micrometer of Gunn Oscillator for required frequency of operation.6. ‘ON’ the Gunn Power Supply, VSWR meter and Cooling Fan.

(a)Voltage-Current Characteriste1. Turn the meter switch of Gunn power supply to voltage position.2. Measure the Gunn diode Current Corresponding to the various voltage controlled by Gunnbias knob through the panel meter and meter switch. Do not exceed the bias voltage above 10 volts.3. Plot the voltage and current readings on the graph as shown in Fig. P12.4. Measure the threshold voltage switch which corresponds to maximum current.

Note: Do not keep Gunn bias knob position at threshold position for more than 10-15 seconds.Reading should be obtained as fast as possible. Otherwise, due to excessive heating, Gunn diodemay burn.

Fig. P12. V-I curve of Gunn oscillator.


(a)Output Power and Frequency as a Function of Bias Voltage1. Turn the meter switch of Gunn power supply to voltage position.2. Increase the Gunn bias control knob.3. Rotate PIN bias knob to around maximum position.4. Tune the output in the VSWR meter through frequency control knob of modulation.5. If necessary change the range dB switch of VS WR meter to higher or lower db position to getdeflection on VSWR meter. Any level can be set through variable attenuator and gain control knobof VSWR meter.6. Measure the frequency by frequency meter and detune it.7. Reduce the Gunn bias voltage in the interval of 0.5 V or 1.0 V and note down correspondingreading of output at VSWR meter and frequency by frequency meter.8. Use the reading to draw the power vs voltage curve and frequency vs. voltage and plot thegraph.9. Measure the pushing factor (in MHz/volt) which is frequency sensitivity against variation in biasvoltage frr an oscillator. The pushing factor should be measured around 8 volt bias.

(c) Square Wave Modulation1. Keep the meter switch of Gunn power supply to volt position and rotate Gunn bias voltageslowly so that panel meter of Gunn Power Supply reads 10 V.2. Tune the PIN modulator bias voltage and frequency knob for maximum output on theoscilloscope.3. Concide the bottom of square wave in Oscilloscope to some reference level and note down themicrometer reading of variable attenuator.4. Now with help of variable attenuator concide the top of square wave to same reference leveland note down the micrometer reading.5. Connect VSWR to detector mount and note down the db reading in VSWR meter for both themicrometer reading of the variable attenuator.6. The difference of both db reading of VSWR meter gives the modulation depth of PINmodulator.

1. Gun Power Supply should be constant.



RESULT

PRECAUTION


To study the function of multihole directional coupler (MHD coupler) by measuring thefollowing parameters:

1. To measure main-line and auxiliary-line VSWR.2. To measure the coupling factor insertion loss and directivity of the coupler.

Microwave sourco (Klystron or (kum Diode type), Isolator, Frequency Meter, Variable Attenuator,Slotted line, Tunable probe, Detector mount, Matched terminator, MHD coupler, Waveguide stand,Cables and accessories,VSWR meter.

A directional coupler is a device with which it is possible to measure the Incident and reflected waveseparately. It consists of two transmission lines, the main arm and auxiliary arm, electromagneticallycoupled to each other. Refer to the Fig. P13. The power entering port 1 in the main-arm dividesbetween port 2 and 3, and almost no power comes out m port 4. Power entering port 2 is dividedbetween port 1 and 4

Where port 4 is terminated with built in termination and power is entering at port 1. The directivityof the coupler is a measure of separation between incident wave and the reflected wave. It ismeasured as the ratio of the two power outputs from the auxiliary line when a given amount ofpower is successively applied to each terminal of the main-lines with other port terminated bymaterial loads.

MULTIHOLE DIRECTIONAL COUPLER

AIM

APPARATUS REQUIRED

THEORY


Where P3F, and P3R is the power measured at port 3 with equal amount ofpower fed to port 1 and port 2 respectively.

Main line VSWR is SWR measured, looking into the main-line input terminal when the matchedloads are placed at all other parts.Auxiliary line VSWR is SWR measured in the auxiliary line looking intothe output terminal when the matched loads are placed on other threeterminals.

Main line insertion loss is the attenuation introduced in transmission line by insertion of coupler. It isdefined as insertion:

When power is entering at port 1.

(a) Main Line SWR Measurement

1 Set up the equipments as shown in Fig. P14.2 Energize the microwave source for particular frequency operation as described. (Procedures givenin the operation of Klystron tube and Gunn Oscillator).3 Follow the procedure as described for VSWR measurement experiment (Low and medium SWRmeasurement).4 Repeat the same for other frequencies.

(b) Auxitia,y Line SWR Measurement1. Set up the components and equipments as shown in the Fig. P14.2. Energize the microwave source for particular frequency operation as described in operation ofKlystron tube and Gunn oscillator.

3 Measure SWR as described in the experiment of SWR measurement (low and medium SWRmeasurement).4 Repeat the same for other frequencies.

PROCEDURE


.

Fig. P15 measurement of insertion loss,coupling &directivity

2. Energize the microwave source for particular operation of frequency.3. Remove the multihole directional coupler and connect the detector mount to the frequency meter.Tune the detector for the maximum output.4. Set any reference level of power on VSWR meter with the help of variable attentuator, gaincontrol knob of VSWR meter, and note down the reading (reference level letX).


5. Insert the directional coupler as shown in Fig. P15 with detector to the auxiliary port 3 andmatched termination to port 2, without changing the position of variable attenuator and gain controlknob of VSWR meter.6. Note down the reading on VSWR meter on the scale with the help of range-db switch if required,let it be Y.7. Calculate coupling factor which will be X-Y in db.8. Now carefully disconnect the detector from the auxiliary port 3 and match termination from port 2without disturbing the set- up.

9. Connect the matched termination to the auxiliary port 3 and detector to port 2 and measure thereading on VSWR meter. Supply it is Z.10. Compute insertion loss X — Z in db.11. Repeat the steps from 1 to 4.

12. 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 thevariable attenuator and gain control knob of VSWR meter.

13. Measure and note down the reading on VSWR meter, let it be YD. 14. Computer the directivity asY — YD .

15. Repeat the same for other frequencies.




RESULT

PRECAUTION


Study of Power Division in a Magic Tee.

Microwave source, Isolator, Variable attenuator, Frequency meter, Slotted line, Tunable probe,Magic Tee, Matched terminations, Waveguide stand, Detector mount VSWR meter and Accessories.

The device magic tee is a combination of E and H plane Tee.Arm 3, the H arm forms an H plane Teeand arm 4, the E arm forms an E plane Tee in combination of arm I and 2 as side or collinear arms.If the power is fed into arm 3 (H-arm), the electrid field divides equally between arm 1 and 2 withthe same phase, and no electric field exists in arm 4. Reciprocity demands no coupling in part 3 (H-arm); if power is fed in arm 4 (E-arm), it divides equally into arm 1 and 2 but out of phase with nopower to arm 3. Further, if the power is fed from arm 1 and 2, it is added in arm 3 (Fl-arm), and it issubstracted in E-arm, i.e., arm 4. Refer Fig. P16.

The basic parameters to be measured for magic Tee are defined below:(a) Input VSWR : Value of SWR corresponding to each port, as a load to the line while other portsare terminated in matched load.(b) Isolation : The isolation between E and H arms is defined as the ratio of the power supplied bythe generator connected to the E-arm (port 4) to the power detected at H-arm (port 3) when side arms1 and 2 are terminated in matched load.

Similarily, isolation between other parts may also be defined.

STUDY OF POWER DIVISION IN A MAGIC TEE

AIM

APPARATUS REQUIRED

THEORY


Where Pi is the power delivered to arm I and Pj is the power detected at j arm.

a) VSWR measurements of the ports

1. Set up the component as shown in fig P 17 Keeping E arm towards, slotted line and matchedtermination to other ports.

2. Energize the microwave source for particular frequency of operation.

3. Measure the VSWR of E-arm as described in measurement of SWR for low and medium value.4. Connect another arm to slotted line and terminate the other port with matched termination. Measure theGVSWR as above. Asabove, VSWR of any port can be measured.

(b) Measurement of Isolation and Coupling Coefficient1. Remove the tunable probe and magin Tee from the slotted line and connect the detector mount toslotted line.

2. Energize the microwave source for particular frequency of operation and tune the detector mountfor maximum output.3. With the help of variable attenuator and gain control knob of VSWR meter, set any power level in

PROCEDURE


the VSWR meter and notedown. Let it be P3.

4. Without disturbing the position of variable attenuator and gain control knob, carefully place themagic Tee after slotted line keeping H-arm to slotted line, detector to E-arm and matchedtermination to arm 1 and 2. Note down the reading of VSWR meter. Let it be P4.

5. Determine the isolation between port 3 and 4 as P3— P4 in db

6. Determine the coupling coefficient from equation given in thetheory part.

7. The same experiment may be repeated r other ports also. .

8. Repeat the above experiment for other frequencies.




RESULT

PRECAUTION


Measurement of VSWR, Insertion Loss, Isolation of isolator and Circulator

Microwave source, isolators Circulators, Frequency meter, Variable attenuator, Slotted line, Tunable probe,Detector mount, VSWR meter, Test isolation and circulation and Accessories.

The isolator is a two-port device with small insertion loss in forward direction and a large in reverseattenuation

The circulator is a multiport junction that permits transmission in certain ways. Refer to the Fig. P18.A wave incident in port 1 is coupled to port 2 only; a wave incident at port2 is coupled to port 3 only and so on. Following is the basic parameters of isolator and circulator forstudy.(a) Insertion Loss: The ratio of power supplied by a source to the input port to the power detectedby a detector in the coupling arm, i.e., output arm with other port terminated in the matched load, isdefined as insertion less or forward loss.

(b) Isolation: It is the ratio of power fed to input ann and the power detected at not coupled portwith other port terminated in the matched load.

(c) Input VSWR: The input VSWR of an isolator or circulator is the ratio of voltage maximum tovoltage minimum of the standing wave existing on the line, when one port of it terminates the line

MEASUREMENT OF VSWR, INSERTION LOSS,ISOLATION OF ISOLATOR AND CIRCULATOR

AIM

APPARATUS REQUIRED

THEORY


and others have matched termination.Note: When port which is not coupled to input port is terminated by matched termination, it makesas Isolator (Two port device).

(a) Input VSWR Measurement1. Set up the components and equipments as shown in Fig. P19. With input port of isolator orcirculator towards slotted line and matched load on other ports of it.2. Energize the microwave source for particular operation offrequency.

3. With the help of slotted line, probe and VSWR meter, find out SWR of the isolator or circulator asdescribed earlier for low and medium SWR measurements.4. The above procedure can be repeated for other ports or for otherfrequencies.

(b) Measurement of Insertion Loss and Isolation

1. Remove the probe and isolator or circulator from slotted line and connect the detector mount tothe slotted section. The output of the detector mount should be connected with VSWR meter.2. Energize the microwave source for maximum output for a particular frequency of operation. Tunethe detector mount for maximum output in the VSWR meter.3. Set any reference level of power in VSWR meter with the help of variable attenuator and gaincontrol knob of VSWR meter. Let it be P1.4. Carefully remove the detector mount from slotted line without disturbing and position of set up.Insert the isolator/circulator between slotted line and detector mount. Keeping input port to slottedline and detector at its output pert. A matched termination should be placed at third port in case ofcirculator.5. Record the reading in the VSWR meter. If necessary change range-db switch to high or lowerposition and taking 10db change for one step change of switch position. Let it is P2.6. Computer insertion loss on P1— P2 in db.7. For measuremext of isolation, the isolator or circulator has to be connected reverse, i.e., outputport to slotted line and detector to input port with other port terminated by matched termination (incase circulator) after setting a reference level without isolator or circulator in the set up as describedin insertion loss measurement. Let same P1 level is set.

PROCEDURE


8. Record the reading of VSWR meter inserting the isolator or circulator as given in step, let it is P3.9. Compute isolation as P1— P3 in db.10. The same experiment can be done for other ports of circulator.11. Repeat the above experiment for other frequencies if needed.




RESULT

PRECAUTION


Measurement of VSWR, Insertion Loss, Attenuation of Fixed and Variable Attenuators

Microwave source Isolator Frequency meter, Variable attenuator, Slotted line, Tunable probe, Detectormount, Matched termination, VSWR meter, Test fixed and variable attenuator and Accessories.

The attenuator are two port bidirectional device which attenuates some power when inserted into thetransmission line.

where P1 = Power absorbed or detected by the load without the attenuator in the line.P2 = Power absorbed/detected by the load with attenuator in the line.The attenuators consist of a rectangular wave guide with a resistive vane inside it to absorbmicrowave power according to their position with respect to side wall of the waveguide. An electricfield is maximum at centre in TE10 mode, the attenuation will be maximum if the vane is placed atcentre of the waveguide. Moving from centre towards the side wall, attenuation decreases in thefixed attenuator, the vane position is fixed where as in variable attenuator, its position can bechanged by the help of micrometer or by other methods.Following characteristics of attenuators can be studied:1. Input VSWR.2. Insertion loss (in case of variable attenuator).3. Amount of attenuation offered into the lines.4. Frequency sensitivity, i.e., variation of attenuation at any fixed position of vane and frequency ischanged.

(a) Input VSWR Measurement1. Connect the equipments as shown in Fig. P21.2. Energize the microwave source for maximum power at any frequency of operation.3. Measure the VSWR with the help of tunable probe, Slotted line and VSWR meter as described inthe experiment of measurement of low and medium VSWR.4. Repeat the above step for other frequencies if required.

MEASUREMENT OF VSWR, INSERTION LOSS,ATTENUATION OF FIXED AND VARIABLE

ATTENUATORSAIM

APPARATUS REQUIRED

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(b) Insertion Loss/Attenuation Measurement1. Remove the tunable probe, attenuator and matched termination from the slotted section in theabove set up.2. Connect the detector mount to the slotted line, and tune the detector mount also for maximumdeflection on VSWR meter (Detector mount’s output should be connected to VSWR meter).3. Set any reference level on the VSWR meter with the help of variable attenuator (not testattenuator) 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 onthe set up. Place the test variable attenuator to the slotted line and detector mount to other port of testvariable attenuator. Keep the micrometer reading of testvariable attenuator to zero and record thereading of VSWR meter. Let it be P2. Then the insertion loss of test attenuator will be P1— P2 db.5. For measurement of attenuation of fixed and variable attenuator, after step 4 of abovemeasurement, carefully disconnect the detector mount from the slotted line without disturbing anyposition obtained upto step 3. Place the test attenuator to the slotted line and detector mount to theother port of test attenuator. Record the reading of VSWR meter. Let it be P3. Then the attenuationvalue of fixed attenuator or attenuation value of variable attenuator for particular position ofmicrometer reading will be P1— P3 db.6. In case of variable attenuator, change the micrometer reading and record the VSWR meterreading. Find out attenuation value for different position of Micrometer reading and plot a graph.

7. Now change the operating frequency and whole step should be repeated for finding frequency sensitivityof fixed and variable attenuator.

Note : For measuring frequency sensitivity of variaole attenuator the positipn of micrometer readingof the variable attenuator should be same for all frequencies in operation.





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Measurement of Phase Shift of a Phase Shifter

Microwave source, Isolator, Variable attenuator, Frequency meter, Slotted line, Tunable probe,Phase shifter, Movable short, VSWR meter, Cables and Accessories.

A phase shifter consists of a piece of waveguide and a dielectric material inside the waveguideplaced parallel to Electric vector of TE10 mode. The phase changes, as a piece of dielectric materialis moved from edge of waveguide towards the centre of the waveguide.

1. Set up the equipment as shown in the Fig. P23.

2. First movable short is placed at the end of slotted line.3. Energize the microwave source for maximum output at particular frequency of operation.4. Find out the λg with the help of tunable probe slotted line and VSWR meter. It is the twice thedistance between two minima on the slotted line.5. Find out the operating frequency for frequency meter or by relation of. λg

6. Find out λ as

7 . Note and record a reference minima position on the slotted line. Let it is X.8. Remove carefully the movable short from the slotted line without disturbing any position on the

MEASUREMENT OF PHASE SHIFT OF A PHASE SHIFTER

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set up, place the phase shifter to the slotted line with its micrometer reading zero and then place themovable short to the other port of phase shifter.

9. Find out a new minima position let it is Y.

10 Change the position of micrometer of phase shifter and find out the corresponding position ofnew minima, let it be yi.

Since a new minimum is multiple of half wave-length, from the short, it should be possible tocalculate the exact electrical length of phase shifter. For example suppose at 10 GHz a referenceminima is found at X = 16.08 cm.Now suppose that phase shifter is two wave-length long and placed on the line as in step 8, the newminima y = 14.90 cm is obtained.Hence, short has apparently moved 16.08 — 14.90 1.18 cm. This canbe written in form of as

Since the apparent movement is in the direction the short actually moved, it is added to theapproximate number of half wave length in the phase shifter. The total electrical length is 2.393wave lengths. The phase shift in radians is found as below:Multiply by 2 π to give phase shift in radius or by 360 degree to give phase shift in degrees.Phase shift in above example=2 π x 2.393 radians= 360 x 2.393 degreesThe phase shift for other micrometer reading position, can be found asabove.




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