Lab Manuals

USMAN INSTITUTE OF TECHNOLOGYHAMDARD UNIVERSITY

DEPARTMENT OF ELECTRICAL ENGINEERING

WAVE PROPAGATION & ANTENNAS (EE-412)SPRING 2014 (CS-LAB)

Engr. Syeda Aimen Naseem

EXPERIMENT # 1: To study different types of transmission and get orientationof the Transmission line (TX-LINE) and antenna trainer.

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TYPES OF TRANSMISSIONTwo-Wire Open Line:This line consists of two wires that are generally spaced from 2to 6 inches apart by insulating spacers. This type of line is mostoften used for power lines, rural telephone lines, telegraph lines,and as a transmission line between a transmitter and an antennaor between an antenna and a receiver. An advantage of this typeof line is its simple construction. The principal disadvantages ofthis type of line are the high radiation losses and electrical noisepickup because of the lack of shielding.

Parallel two-wire line:This type of transmission line is commonly used to connect atelevision receiving antenna to a home television set. This lineis essentially the same as the two-wire open line except thatuniform spacing is assured by embedding the two wires in alow-loss dielectric, usually polyethylene. Since the wires areembedded in the thin ribbon of polyethylene, the dielectricspace is partly air and partly polyethylene.

Twisted Pair: .As the name implies, the line consists of two insulated wirestwisted together to form a flexible line without the use ofspacers. It is not used for transmitting high frequency becauseof the high dielectric losses that occur in the rubber insulation.When the line is wet, the losses increase greatly.

Shielded Pair:Consists of parallel conductors separated from each othersurrounded by a solid dielectric, the conductors are containedwithin braided copper tubing that acts as an electrical shield.The assembly is covered with a rubber or flexible compositioncoating that protects the line from moisture and mechanicaldamage.The principal advantage of the shielded pair is that theconductors are balanced to ground; that is, the capacitancebetween the wires is uniform throughout the length of the line.This balance is due to the uniform spacing of the groundedshield that surrounds the wires along their entire length. Thebraided copper shield isolates the conductors from straymagnetic fields.

Coaxial LinesThere are two types of COAXIAL LINES, RIGID (AIR) COAXIAL LINE and FLEXIBLE(SOLID) COAXIAL LINE. The physical construction of both types is basically the same; thatis, each contains two concentric conductors.

Rigid (Air) Coaxial LineThe rigid coaxial line consists of a central, insulated wire

(inner conductor) mounted inside a tubular outer conductor.In some applications, the inner conductor is also tubular. Theinner conductor is insulated from the outer conductor byinsulating spacers or beads at regular intervals. The spacersare made of Pyrex, polystyrene, or some other material thathas good insulating characteristics and low dielectric losses athigh frequencies.The chief advantage of the rigid line is its ability to minimizeradiation losses.. The fields are confined to the space betweenthe two conductors, resulting in a perfectly shielded coaxialline. Another advantage is that interference from other lines isreduced. The rigid line has the following disadvantages: (1) itis expensiveto construct; (2) it must be kept dry to prevent excessive leakage between the twoconductors; and (3) high-frequency losses are less. Leakage caused by the condensation ofmoisture is prevented in some rigid line applications by the use of an inert gas, such asnitrogen, helium, or argon. It is pumped into the dielectric space of the line at a pressure thatcan vary from 3 to 35 pounds per square inch. The inert gas is used to dry the line when it isfirst installed and pressure is maintained to ensure that no moisture enters the line.

Flexible coaxial line:Lines are made with an inner conductor that consists offlexible wire insulated from the outer conductor by a solid,continuous insulating material. The outer conductor is madeof metal braid, which gives the line flexibility. Early attemptsat gaining flexibility involved using rubber insulatorsbetween the two conductors. However, the rubber insulatorscaused excessive losses at high frequencies. Because of thehigh-frequency losses associated with rubber insulators,polyethylene plastic was developed to replace rubber andeliminate these losses. Polyethylene plastic is a solidsubstance that remains flexible over a wide range oftemperatures.It is unaffected by seawater, gasoline, oil, and most other liquidsthat may be found aboard ship. The use of polyethylene as an insulator results in greater high-frequency losses than the use of air as an insulator. However, these losses are still lower thanthe losses associated with most other solid dielectric materials.

ANTENNAReflectometric Bridge:Used for the measurement of forward and reflected power in transmission lines; this usuallybeing expressed in terms of SWR or return loss (to be defined shortly).

Dipole Antenna:A dipole antenna is a radio antenna that can be made of a simple wire, with a center-fed drivenelement. It consists of two metal conductors of rod or wire, oriented parallel and collinear witheach other (in line with each other), with a small space between them. They are used alone asantennas, notably in traditional "rabbit ears" television antennas, and as the driven element inmany other types of antennas, such as the Yagi.

Slot Antenna:A slot antenna consists of a metal surface, usually a flat plate, with a hole or slot cut out. Theshape and size of the slot, as well as the driving frequency, determine the radiation distributionpattern. Slot antennas are widely used in radar antennas, for the sector antennas used for cellphone base stations.

Spiral Antenna:It is shaped as a two-arm spiral, or more arms may be used. Spiral antennas belong to the classof frequency independent antennas which operate over a wide range of frequencies.Polarization, radiation pattern and impedance of such antennas remain unchanged over largebandwidth.

Yagi-Uda Antenna:It is a directional antenna system consisting of an array of a dipole and additional closelycoupled parasitic elements (usually a reflector and one or more directors). The dipole in thearray is driven, and another element, typically 5% longer, effectively operates as a reflector.Other parasitic elements shorter than the dipole may be added in front of the dipole and arereferred to as directors. This arrangement increases antenna directionality and gain in thepreferred direction over a single dipole. Yagi antennas are commonly used for reception oftelevision broadcasts.





EXPERIMENT # 2: Analysis of transmission line with different characteristics oftransmission line trainer (ST2266)

Characteristics of the line Input impedance of the line Attenuation of the line

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BASIC PROPERTIES OF THE COAXIAL CABLE(used in the trainer)

Type: RU 174Length: 100 metersSeries Inductance: 280uh (Frequency 1 KHz, 100 m) approx.Parallel capacitance: 1pF (Frequency 1 KHz, 100 m) approx.Conductance: 0.4 p mhosImpedance: 50 approx.

INSTRUMENTS REOUIRED FOR EXPERIMENTATION

1. 20 MHz Dual Trace Oscilloscope ST201.2. 31/2 Digits Digital Multimeter.3. L C R Q Meter or Universal L C R Bridge.4.

Important points to note:1. The coaxial line used in the trainer is placed in the coiled form of 25 meters each. This is

done for space saving. In practice the lines are straight. The coil form has caused somedeterioration. For the convenience of the students the basic properties given above are ofcoiled form.

2. The attenuation of RU 174 cable is 40dB / 100 m at 200 MHz But due to coiled form itwill show 3dB/ 100 in at 3.6 MHz

3. In place of internal sine wave test generator you may use other generator of higherfrequency.

OBJECT # 01: MEASURING THE CHARACTERISTICS OF A LINE

A coaxial line can be considered as cascaded of line trunk. Each of them can be represented asbeing composed of resistive, inductance and capacitive circuit element.L = inductance for unit lengthG = conductance for unit lengthC = capacitance for unit lengthThe transmission characteristics of a line are described in terms of propagation (constant )these parameters are typical values for each single line. The same is true for the capacitance,the inductance, the resistance and the conductance for length unit. In the telecommunicationsfield, these values are generally expressed per meter or kilometer, for practical reasons. In thiscase, the symbol used to indicate these magnitudes are the common symbols. This experimentmeasures the characteristic parameters such as R, L, C, G, Zo and r for the transmission lineincluded in this trainer.

PROCEDURE:

1. Figure shows the modalities for the measurement to be performed.2. Make connections as in Fig 1.3. Both the inductance and the ohmic resistance of the line are measured in series by shortcircuiting end of the line and connecting the measuring instruments to the start of the line. Thecapacitance and the conductance are measured in parallel by operating on the open line.

4. The resistance R and the conductance G can be measured with an ohmmeter or DMM. Forthe conductance to be measured an ohmmeter is required which is able to perform resistancemeasurements with a range greater than 100 M.

5. For the measurement of series inductance L and the parallel capacitance C, a LCR meter ormeasuring bridge is required. The results of these measurements give values of R, L, C and Greferred to the cable length that, in our case, is of 100 meters. Zo can be measured by using thefollowing formula:

Z0= (L/C)



Z0= (L/C)



Z0= (L/C)

OBJECT # 02: MEASURING THE INPUT IMPEDANCE OF THE LINE.

The input impedance of the line depends on features like the ohmic resistance, theconductance, the inductance and the capacitance. It is also related to the resistance that loadsthe line at the opposite end and to both the frequency and voltage of the signal. The purpose ofthe first part of the test is to measure the 1/P impedance of the line under different loadconditions:1. Line terminated with matched load2. Open line3. Short-circuited line.In the second part of the test we will measure the phase displacement between the input voltageand current; under the 3 conditions of line termination. When the modulus and the phasedisplacement are known the impedance vector is fully identified.

PROCEDURE:1. Adjust RI and RL for 18 and 68 respectively with the help of DMM.2. Make connections as shown in Fig. 2b.3. A 1 resistance in series between the generator and the transmission line.4. Set the input at 0.4Vp-p and freq 100 KHz of sine wave (both measurement on CRO).5. Take readings of Vin and Vm (across 1K) on oscilloscope.6. Calculate the input impedance according to the following formula:

Z in= V in / I= (Vin/Vm) x 17. Change the frequency of 1 MHz and note the values of Vin and Vm at this frequency.8. Note down these results. The input impedance at 100 KHz is around 80 and at 1MHz isaround50

Parameter Vin Vm ZinLow FrequencyHigh Frequency











OBJECT # 03: MEASURING THE ATTENUATION OF THE LINE.

The ohmic resistance R & the conductance G are responsible for energy dissipation in the formof heat. These losses determine the attenuation. Characteristics are expressed in terms of"attenuation" "a" and can be calculated by:

a=20 log (V2/V1)Where VI = amplitude of signal at I/PV2 = amplitude of signal at 0/Pa = attenuation for given lengthIn this experiment we will measure the attenuation for the different trunks of transmission lineavailable on the trainer.







Concept of matched line:Though the concept of match line is not treated in detail in this manual but the subject iscertainly known to the students from the theoretical course. We have already found out thecharacteristic impedance of the line as 50 from the previous experiment. The short-circuitedresistance of the line when measured with Digital Multimeter is shown to be 18. Therefore;the total effective resistance of the line is 68. For optimum power transfer we should have thesource resistance and terminating resistance also as 68. Assuming generator resistance as50, for this purpose, the student must set Ri to 1 this setting RL to 68 initially

PROCEDURE:1. Adjust Ri and RL for 18 and 68 respectively with the help of DMM.2. Make connections as shown in Fig 3b.3. Set the sine-wave frequency to approx 100 KHz and level to 0.4 V.4. Oscilloscope CH 1 shows applied input CH 2 shows outputs.5. Measure signal level at Input, and at 25, 50, 75, and 100 m lengths.6. Tabulate as under:Length (m) V1(input) V2 (output) Attenuation(a)

255075100

7. Now, calculate the attenuations in dB at various lengths by the formula given below: a = 20Log V2/ V1.8. The attenuation is approx -2 dB at 100 m.9. Try the same with open-ended line and short-ended line



255075100




255075100


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Stationary waves Frequency characteristic of the line. Phase displacement between the current & voltage at input of line

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OBJECTIVE#1: STUDY OF STATIONARY WAVES

A line that has not been terminated with a load equal to its characteristic impedance is subject to areflection phenomenon of the power from the remote end. The amount of the reflected powerdepends on the amount of mismatch between the characteristic impedance of the line and the loadimpedance. In the extreme cases of short-circuited line (RL = 0) and open line (RL=), situationof total reflection occur for either the current wave or the voltage wave. The purpose of this test isto study the establishment of the stationary waves within the line.

PROCEDURE:1. Adjust Ri, and RL for 18 and 68 respectively with the help of DMM.2. Make connections as shown in Fig.163. Set oscilloscope to 0.1 V / div for both channels.4. Adjust the sine generator for a output of 0.2 Vp-p (2 div Deflection on CH 1) and at

frequency 100 KHz.

5. Observe the peak to peak voltages on CH 2 at 100 m and at intermediate sockets at 75 m, 50m & 25 m and Om.

6. Tabulate results as under :

DISTANCE V p-p0m25m50m75m100m




frequency 100 KHz.







frequency 100 KHz.




Calculate the stationary wave ratio ls' by the following formula: (For 100 KHz ls' is approx.1.25)

SWR=_______________

7. The reflection coefficient 'r' of the line shows how much of the energy supplied at the UP isbeing reflected as a consequence of the load decoupling. The reflection coefficient is normallyexpressed in percentage and can be determined from the stationary wave ratio through thefollowing formula: (At 100 KHz 'r' is approx. 1I %)

r =________________

OBJECTIVE#2: FREQUENCY CHARACTERISTIC OF THE LINE.

Frequency of the input signal increases, the line attenuation due to both the ohmic resistance(R)and the conductance (G) progressively increases because of "Skin effect. The cut off frequencyof the line is defined as the frequency at which the attenuation reaches the level of -3dB comparedto the low frequency level -3dB is approximately down to 70 %.The purpose of this test is to measure the cut off frequency for the coaxial Line provided inST2266. This measurement is performed with terminated line.

PROCEDURE:1. Adjust Ri and RL for 18 f and 68 D respectively with the help of DMM.2. Make connections as shown in Fig. 14.3. Set oscilloscope to 0.1 V / div for both channels.4. Adjust the sine generator for an output of 0.2 Vp-p (2 div. deflection on CHI) and at

frequency 40 KHz.5. At this point CHI is reading 2 div. deflections and CH2 is reading 1,6 div. (This is due to

the fix attenuation of the line)6. Now, vary the frequency of generator gradually keeping the input amplitude constant

(observe CH 1 and maintain 2 div deflection by adjusting AMP VAR control) till thewaveform at the end of 100 m line falls to -3 dB (1.4 div of CH 2 on the oscilloscope).

7. Note, this frequency on the oscilloscope. This frequency is known as the cut offfrequency.

8. For the cable used in this trainer this frequency is approximately 3.5 MHz


SWR=_______________


r =________________










SWR=_______________


r =________________









OBJECT #3: PHASE DISPLACEMENT BETWEEN THE CURRENT & VOLTAGE ATINPUT OF LINE.The phase displacement between the current & voltage at input of line, under the different loadConditions viz. matched line, open line and short-circuited line, See Fig. 1a.

PROCEDURE:1. Adjust Ri and RL for 18 and 68 respectively with the help of DMM.2. Make the connections as shown in Fig. 1b.3. A1 resistance in series between the generator and the transmission line as shown, inFig.1b allows measuring the value of input current.4. Set sine wave frequency to 100 KHz (use CRO).5. Set the oscilloscope to XY mode.6. Output across 1 is connected to Y and input signal is connected to X.7. Observe suitable Lissajous pattern on CRO by adjusting V / div of each channel.





8. The Lissajous pattern allows measuring the phase displacement between the two signalsthrough the ratio of the semi axis of the ellipse. The phase displacement is approx. 15 at 100KHz.

OBSERVATION:Y1 Y2

Fig 1b

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OBSERVATION:Y1 Y2

Fig 1b

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OBSERVATION:Y1 Y2

Fig 1b

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Fault localization within the line. Line under pulsed condition.

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OBJECTIVE 1: FAULT LOCALIZATION WITHIN THE LINE.

The Localization of the faults within the line can be performed following different methods. Themethod shown here for performing this test is of special interest, being based upon the use of thephenomenon of the establishment of stationary waves, Let's assume that the line is broken atunknown point between two ends.'"If the line is connected to a signal generator, the wave will bereflected from the break point, and a stationary wave condition is established between the I/P andthe breakpoint. The waves along the line have maximum and minimum points at regular intervalscorresponding to 1/4 of the wave - length of the I/P signal. For the fault to be pinpointed, it isnecessary to determine, the frequency value at which a voltage minimum occurs at the I/P. Thisfrequency is noted as . The same operation is repeated at the remote end, of broken cable, andobtaining f2 value. These values are substituted in the following formula:

L=[f2/(f1+f2)]xlWhere,1= line length in meters1' = distance in nits of the point of fault referred to the UP -of the line.

PROCEDURE:

1. Make connections as shown in Fig. 20 a. Note that the line is broken at 50 m length.2. Set oscilloscope channel 1 to 0.1 V/ div.3. Adjust the sine generator for 0/P of 0.4 V p-p (4 div deflection on CH 1).4, Keep the frequency variable control at the minimum position5. Gradually increase the frequency and note the frequency at which the signal on CRO falls

to minimum. This frequency is fl.6. Repeat the test at the other end of the line as shown in Fig. 20 b and note the Frequency at

which signal on CRO falls to minimum. This is 12.7. Enter these values in the formula and calculate the distance of break point from the I/P.

For the fault generated at 50 m fl and 12 are 900 KHz approx.

Observation:F1=_________________ F2=_________________

L = _________________ L=_________________

OBJECTIVE-2: LINE UNDER PULSED CONDITION.

If the line is supplied with a pulsed signal and the line is not matched at the ends, the pulses sentinto the line will be more or less reflected as a function of the mismatch. The reflected fraction ofthe pulse moves along the line in the opposite direction to the generator and when thecharacteristic impedance of the line is not matched to the impedance of the generator it is againreflected to the other end. The purpose of this test is to study the propagation of the pulse edgesalong the line, under different matching conditions viz. open line, short circuited line & matchedline.

Observation:F1=_________________ F2=_________________

L = _________________ L=_________________



Observation:F1=_________________ F2=_________________

L = _________________ L=_________________



PROCEDURE :1. Adjust Ri, and RL for 18 0 and 68 S2 respectively with the help of DMM.2 Make connections as shown in Fig.22.3. Observe the I/P and 0/P wave shapes and also amplitude levels on the Oscilloscope.4. Now make the load open and repeat the same procedure.5. Again, repeat the experiment for short-circuited load.6. Note the observations for all 3 conditions of load and compare them

Observation:Conditions Waveform

For MatchedCondition

For Open Load

For Short CircuitedLoad

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For Open Load


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For Open Load


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EXPERIMENT # 5: To study the reflectometer and calculate the SWR for a coaxial cableat different frequencies

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STUDY OF STANDING WAVE RATIO AND REFLECTION COEFFICIENT:Standing Wave Ratio: The SWR is usually defined as a voltage ratio called the VSWR (voltagestanding wave ratio) is the measurement of maximum voltage (current) to minimum voltage(current) on a transmission line and measures the perfection of the termination of the line.A problem with transmission lines is that impedance mismatches in the cable tend to reflect thetransmitted waves back toward the source end of the cable, preventing all the power fromreaching the destination end. SWR measures the relative size of these reflections. An idealtransmission line would have an SWR of 1:1, with all the power reaching the destination and noreflected power. The voltage component of a standing wave in a uniform transmissionline consists of the forward wave (with amplitude ) superimposed on the reflected wave (withamplitude ).

Reflection Coefficient Reflections occur as a result of discontinuities, such as an imperfection inan otherwise uniform transmission line, or when a transmission line is terminated with other thanits characteristic impedance. The reflection coefficient is defined thus:

.

For the calculation of VSWR, only the magnitude of , denoted by , is of interest.The voltage standing wave ratio is then equal to:

OBJECT#1: STUDY OF THE REFLECTOMETER:

PROCEDURE: Connect the generator to the input of the reflectometer given in figure with a cable of 9cm,

75 . The output marked as OUTSCOPE.

: maximum negative reflection, when the line is short-circuited: no reflection, when the line is perfectly matched: maximum positive reflection, when the line is open-circuited



.








.






Apply 75 to the bridge port, marked Zn keeping the part Zx load less. Turn the potentiometer OUTLEVEL clockwise turn switch HI/LOW to the position HI. The modulation is not used and so it must b disconnected. Turn the generator on the frequency meter should indicate 701.5 MHZ; remember that this

frequency can b obtained easily by pressing up and down. The voltage measured by the voltmeter adjust the OUTLEVEL to take the reading to known

value for example 300 mV Now connect the second 75 termination to the port marked as Zx, the output decrease to

the zero because the bridge will balance. By varying the frequency the output willconstantly null because behavior of impedances Zn and Zx ill be same at all range offrequencies

Connect 50 to port Zx the SWR in this case:75/50=1.5

The reflection coefficient or the ratio of reflected to incident voltages is = (SWR-1)/ (SWR+1) = 1.5-1/1.5+1=0.2

Connect 100 instead of 50 to the port Zx, the SWR is now 1.333 i.e. the reading ofSWR is slight different as previous one.

OBJECT#2: MEASUREMENT FOR EACH FREQUENCY:PROCEDURE: Set the generator at a certain frequency (for example 701.1MHZ) and regulate the

amplitude of the generator to obtain a reading of 300mv. This voltage is the referencevalue corresponding to a total reflection at the end.

Connect generator, rho-tector, cables and multimeters as shown in figure below

The ratio of voltages measured with the multimeter to the reference voltagescorresponding to the total reflection is the reflection coefficient of load ZL connected tothe 75 ohms lines. In the theory, being in perfect matching conditions between line andload (Z0=ZL=75ohms), the reflection coefficient should b null

Insert ZL=50 and 100 ohms with direct load and with transmission line load the reflectioncoefficient is different in respect to last case

From the formula: SWR= (1+)/ (1- ), measure at different frequencies.































EXPERIMENT # 6: To observe the Impedance Transformation property of Transmissionlines

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IMPEDANCE TRANSFORMATIONThe presence of the standing wave is due to the energy the line if the line is the most, namely itla open- or short-circuited, the reflection is total.An ideal line terminated on its characteristic impedance is perfectly transparent: voltage andcurrent are constant on each of its points and so also the measured impedance is constant.With standing wave, voltage and current vary along the line, repeating with reduced wave lengthin respect to the frequency one, caused by the different propagation speed.as the voltage and current keep constant at any half wavelength, also when standing wave, arepresent, they will be the same at a distance of a whole number of wavelength from the load, sothe impedance to be measured is the one of the mismatched load, whatever the characteristicimpedance is.if the line is open-circuited, in fact, there is a voltage antinodes, due to the numb of incident andreflected waves, at half wavelength from its end; if the line is short-circuited there is a node,namely the voltage is nullBut, at a quarter wavelength and with a short-circuited line, there le the same antinodes of anopen line under the: same conditions: we can say that a quarter wave length transforms theimpedance.As halt wavelength line segment don't transform impedance the same can be applied to 3/4, 5/4,etc wavelength lines. this is true if the characteristics impedance of the line is always the same,but if the quarter wavelength segment has different characteristic impedance we obtain the samebehavior, which is a value transformation of the impedance from calculation, we obtain theformula which gives the ratio between characteristic impedance it of the quarter wavelengthsegment and the input and output impedances at and z0.Lets see an application of the above said by using the rho-tector (fig).

apply a signal of 300v with the termination Zn=75 ohm; the line length betweengenerator and rho-tector is not important, consequently we'll use a cable of 1 m (75 ohm)connect ex to a cable of 50 ohm (connect at the other end of the cable the female-femaleadapter), 43 cm long, which corresponds to 3 half wavelengths around 700 mhz.

Terminate the cable with 75 Ohm and vary the frequency around 701.1 MHz to obtain theminimum reading on the multimeter. This means, at this frequency, where in matchingconditions, although the line and the load have different Impedance







Push keys UP and DOWN together to go back to 701.5 MHz and regulate the sensibilityof the oscilloscope to take the trace to the upper limit of the screen or, Let's suppose touse a 300 mV value in our examples,

Now connect the second 75 ohm termination to the Port marked as Zx the output willdecrease to zero because the bridge will be balanced. On varying the frequency, theoutput will keep constantly zero, because the behavior of impedances Zn and ZX will thesame at different frequencies

Connect 50 Ohm to the port Zx. The SWR in this case7550=1.5 The reflection coefficient, or ratio of the reflected to the incident voltage, is

RHO= SWR-1SWR+1= 1.5-11.5+1 = .PROCEDURE:

1. In order to check the 300ohms impedances proceed as follows:2. Connect generator, Reflectometric Bridge and balun 4:1as in figure the balun transform,

with a ratio 4:1, the impedance at its terminals. The 75 ohms seen by the balun toward theReflectometric bridge are transform into 300 ohm to t the balun terminals, and note thereduction of measured SWR

3. Terminate the balun terminals with the 300 ohms line, terminated with a 300 ohmresistance too and note a decrease of SWR which is analoguous to the last case

4. The 75 ohms line impedances are checked in a similar way by using a 1:1 balun and the75 ohm line.

Fig 1 Fig2

OBSERVATION CHART AND RESULTS:





EXPERIMENT # 7: To observe the frequency response of simple dipoles and foldeddipoles

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FOLDED DIPOLE Current distribution in the wire which is fed at

one end with high frequency source issinusoidal its value will be zero after quarterwave and then it will change sign andconsequently direction in space

If the segment above the quarter wave is foldedover the quarter wave before it , the currenthave the same direction

Frequency Response of the Folded DipoleIn order to measure the Frequency response of the folded dipole we must use the balun 4:1which transform the impedance from 300 to 75 ohms connect generator rho rector cables andmulti meter as in figure

SIMPLE DIPOLE THIN AND THICK DIPOLE The simple dipole is one of the basic antennaits characteristic impedance is 73 ohms Theoretically the dipole length is half wave length I diameter ratio is infinite usually

there is a shorting Coefficient k(ranging from 0.9 to .99) according to which the half wave length in free

space must be multiplied in order to have the half wave dipole length once the diameterof conductor

Frequency Response in Simple DipoleMeasurement can be taken in correspondence to the single frequency value or, by using thesweep for a determine frequency interval

















MEASUREMENT FOR SINGLE FREQUENCIESPROCEDURE:

1. Connect generator rho-rector cables and multimeter as in figure set the generator at701.5 connect the short circuit termination to ZL and regulate the generator to obtain areading of 100mv on the multimeter this voltage is a reference value corresponding toa total reflection situation

2. Remove the short circuit and connect the load ZL constituted by the thick short dipole3. The ratio of the voltage measured now on the multi meter to the reference on which

corresponds to the total reflection (100mv in the present case ) is the dipole reflectioncoefficient in theory coefficient should be null as being in normal matching conditionbetween line and load (z0-z1=75 ohm) actually a the reflection value RHO will bemeasured caused by mismatching

4. from this ratio SWR=1+rho1-rho we can determine the standing wave ratio

5. Repeat above process by replacing thick short dipole to thin long dipole.6. Repeat above process by replacing thin long to folded dipole shown in figure below

20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1

S. NO

OBSER

VA

TION

CH

AR

T LA

B # 07

BASE

VO

LTAG

E (V

m) U

SING

THE

SHO

RT

CIR

CU

ITED TER

MIN

ATO

R IS

TO SET

300m

v

FREQ

(MH

Z)

Thin-

Long

Dip

ole

REFLEC

TED V

OLTA

GE

(VR)

IN M

V

Thin-

Short

Dip

ole

Folded

Dip

oleThin

-

Long

Dip

ole

RH

O

Thin-

Short

Dip

ole

Folded

Dip

oleThin

-

Long

Dip

ole

SWR

Thin-

Short

Dip

ole

Folded

Dip

ole

RESULTS:Center Frequency for the Thin-Long DipoleCenter Frequency for the Thick-Short DipoleCenter Frequency for the Folded Dipole





EXPERIMENT # 8: To observe the frequency response of the BATWING andSPIRAL antennas

Name of Student: __________________________________________________________________

Roll No.: ______________________________________Group:_____________________________

Date of Experiment : __________________________________________________

Report Submitted on : __________________________________________________

Marks Obtained : __________________________________________________

Remarks if any : __________________________________________________

Signature : __________________________________________________






Name of Student: __________________________________________________________________

Roll No.: ______________________________________Group:_____________________________



Marks Obtained : __________________________________________________

Remarks if any : __________________________________________________

Signature : __________________________________________________






Name of Student: __________________________________________________________________

Roll No.: ______________________________________Group:_____________________________



Marks Obtained : __________________________________________________

Remarks if any : __________________________________________________

Signature : __________________________________________________

SPIRAL ANTENNA The spiral antenna belongs to those antennas which are frequency independent, which

means that they have an extremely large bandwidth.

The spiral antennas can be plane or disc one type, with arms varying from 2 to 6.

The impedance of a spiral antenna with two arms is around 70-100 ohm.

The radiation diagram depends on the number of the arms, and its particularity lies 'In thefact that, in theory, it is independent. Actually there are asymmetries depending on thefrequency, caused by the finite dimensions of the arms of the spiral.

FREQUENCY RESPONSE OF THE SPIRAL ANTENNAConnect generator, rho-tector, cables and multimeter as in fig.4.19, and repeat measurementscarried, out for the simple dipole (par.4.3.1). All the generator range has a good matching













OBSERVATION CHARTBASE VOLTAGE (Vm) USING THE SHORT CIRCUITED TERMINATOR IS TO SET 300mvS. No FREQ (In

MHz)BATWING ANTENNA SPIRAL ANTENNA

Reflectionvoltages

RHO SWR Reflectionvoltages

RHO SWR

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

RESULT: ____________________________________________________________________





EXPERIMENT # 09: To plot the radiating pattern of THICK SHORT and THINLONG dipoles antennas

Name of Student: ___________________________________________________________________

Roll No.: _______________________________________Group:_____________________________

Date of Experiment : ___________________________________________________

Report Submitted on : ___________________________________________________

Marks Obtained : ___________________________________________________

Remarks if any : ___________________________________________________

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