-
7/25/2019 Impedane Lab
1/5
Objectives:
1- Determine impedance using slotted line
2- Determine impedance using smith chart
Introduction:
In this experiment we will use a waveguide slotted line and
smith chart to study the basicbehavior of standing waves and to
measure SWR, guide wavelength, and compleximpedance. Slotted lines
can be made with any type of transmission line (waveguide,
coax,etc.), determining the place of two minima .
Components:
Gunn Oscillator. Gunn Oscillator power supply.
Thermistor Mount.
SWR Meter.
Variable Attenuator.
Slotted Line.
Fixed Attenuator -6dB.
Cables and Accessories
2 waveguide support.
Fixed short circuit.
Procedure:
1. All power switches must be off. Set up and assemble the
components as shown
below.
-
7/25/2019 Impedane Lab
2/5
2. On the slotted line, adjust the depth of the probe to the
second uppermost mark.3. Move the slotted line probe to the 40.0 mm
position.4. Make the following the adjustment to the
Gunn-Oscillator power supply:
(voltage = Min, Mode = 1KHz, Meter Range = 10V)5. Make the
following the adjustment to the SWR meter
(Range = 0dB, Scale = Normal, Gain = min, Center Freq = mid, BW
= 20Hz).6. Turn on the Gunn Oscillator power supply. Wait about 1-2
minutes to warm up,Adjust the supply voltage to 8.5 V.
7. Measure the distance between two minima nearest to the
shorted load.8. On the slotted Line, slowly move the probe until
you encounter maxima.9. On the SWR-Meter, Adjust the Center freq to
maximize the needle deflection.
10. A Move the probe until you encounter the first Null1.
Null1 = 54.5 mm.
11.Slowly move the probe towards the source until you encounter
Null2 = 78mm.
12.From the data recoded, calculate the guided wavelength as =
=. = . =
13.Disconnect the Gunn Oscillators power supply cable. Assemble
the setup below.
14. Adjust the variable attenuator to 4dB and 2.32mm Blade
Position.
15. Reconnect the Gunn Oscillators power supply cable.
16.On the SWR meter select the range that you use to detect
maximum earlier. On
the slotted line move the probe until you encounter the voltage
maximum closest to
the load.
-
7/25/2019 Impedane Lab
3/5
17.On the SWR-meter set the Gain control to obtain a reading of
0 dB. If this is not
possible, select the next range of SWR meter and adjust the Gain
to obtain 0dB.
18.Move the slotted line until you encounter the minimum located
between the minima
previously observed.
=. =.
a. Calculate the distance d between as:
= = . =.b. Calculate the phase of the reflection coefficient
as:
=
= .
=.
c. Plot the circle corresponding to the measured SWR on the
smith Chart provided,
draw a radius corresponding to angle and determine normalized
load impedance =
d. Adjust the variable attenuator to 2dB which corresponds to
2.62 mm blade position.
e. Repeat steps a to c for this load, and the result is :-
=. =. = = . =.
= = . =.
From graphical :-
=
f. Turn off the Gunn Oscillators power supply cable.
-
7/25/2019 Impedane Lab
4/5
g. It is required to verify the unknown load impedance by using
specific formulas as
follows:
For SWR1 =.
= + =..+ =.
=..
=
+
=+ ..
.
.
=
.
.
For SWR2 =.
= + =..+ =.
=..
= +
= +
.
.
.. =..
19 .Repeat again with matched load
= =
20 . Repeat again with open
= =
-
7/25/2019 Impedane Lab
5/5
Comments:
The impedances in Smith Chart is normalized impedance with
respect thecharacteristic impedance.
= 0 + 0 The distance between two successive minima of the
standing wave is measured with
the slotted line and the SWR meter.
Conclusion:
we study how use a Smith Chart to understand two ways unknown
impedance by theslotted Line . and confirm this by smith chart.
