1. IMPEDANCE MATCHING & SMITH CHART

2. Impedance Matching of RF Transmission Lines :
Basic requirements needed for a better transmission line
High transmission efficiency
Very small VSWR
Can able to operate over a range of frequencies.
All the above will be affected due to mismatch problems.

3. Effects of Mismatch : Power loss in feeder line.
Transmission line may damage.
Frequency stability problem in generator.
Signal get reduced due to reduction of signal-to-noise ratio.
In order to avoid the problems we need a Matching Network.
Different types of impedance matching :
Reflection less match
Conjugate match
Zo match

4. Reflection less match
Conjugate match
Zo match

5. Types of Matching Network :
Impedance matching using L or C of a transmission line.
Impedance matching using L- C of a transmission line.
Impedance matching using quarter wave transformer.
Impedance matching using half wave lines.
Impedance matching using short circuit stubs.
Stub Matching : [ Tuning Stubs]
For high microwave frequencies, a section of a transmission line can be used as matching network at suitable distances.
It can be connected in two ways (OC & SC)
1. Series (series reactance)
2. Parallel (Shunt reactance )

6. Types of Stubs :
Single Stub
Double stub
Triple stub

7. Figure Reflection and transmission at the junction of two transmission lines with different characteristic impedances.

8. Figure (a) Voltage, (b) current, and
Short-circuited line
Figure (a) Voltage, (b) current, and
(c) impedance (Rin = 0 or ) variation along a short-circuited transmission line.

9. Open-circuited line
Figure (a) Voltage, (b) current, and (c) impedance (Rin = 0 or ) variation along an open-circuited transmission line.

10. Figure Voltage standing wave patterns (a) Standing wave for short-circuit load. (b) Standing wave for unknown load.

11. The Slotted Line
A transmission line allowing the sampling of E field amplitude of a standing wave on a terminated line.
With this device the SWR and the distance of the first voltage minimum from the load can be measured, from this data ZL can be determined.
ZL is complex  2 distinct quantities must be measured.
Replaced by vector network analyzer.
Assume for a certain terminated line, we have measured the SWR on the line and lmin , the distance from the load to the first voltage minimum on the line.

12. An X-band waveguide slotted line.

28. Impedances, voltages, currents, etc. all repeat every half wavelength
Smith Chart
Impedances, voltages, currents, etc. all repeat every half wavelength
The magnitude of the reflection coefficient, the standing wave ratio (SWR) do not change, so they characterize the voltage & current patterns on the line
If the load impedance is normalized by the characteristic impedance of the line, the voltages, currents, impedances, etc. all still have the same properties, but the results can be generalized to any line with the same normalized impedances
The Smith Chart is a clever tool for analyzing transmission lines
The outside of the chart shows location on the line in wavelengths
The combination of intersecting circles inside the chart allow us to locate the normalized impedance and then to find the impedance anywhere on the line

29. Smith Chart – Real Circles

30. Smith Chart – Imaginary Circles
x=1/3
x=1
x=2.5
x=-1/3
x=-1
x=-2.5
Smith Chart – Imaginary Circles

31. Smith Chart