The document discusses impedance matching techniques, focusing on the single stub matching method as an alternative to the quarter wave transformer, which is frequency sensitive. A single stub is an open or shorted transmission line section connected to the main line and characterized by its length and position relative to the load. Preference for using a shorted stub over an open stub is noted due to reduced radiation and ease of implementation, although both options have practical considerations.

1. Impedance Matching
Single Stub Technique
Why not Quarter wave transformer for matching?
Quarter wave transformer is narrow-band or
frequency sensitive device.
What other option is?
Stub Tuner matching technique.
What is Stub tuner?
It is an open or shorted section of transmission
line of length d connected in parallel or series
with the main line at some distance from the
load.

2. Impedance Matching
Single Stub Technique
• Stub has the same characteristic
impedance as that of the main line.
• Series stub is difficult to use as
compared to parallel stub.
• An open circuit stub radiates
energy at high frequency so shunt short
circuited stub is preferred.

3. Impedance Matching
Single Stub Technique
For stub matching, we intend

4. Impedance Matching
Called single stub matching.

5. Impedance Matching
Single stub matching
There are two design parameters for single stub matching:
• The location of the stub with reference to the load dstub
• The length of the stub line Lstub
The transmission line realizing the stub is normally terminated by a
short or by an open circuit. In many cases it is also convenient to select
the same characteristic impedance used for the main line, although this
is not necessary.

6. The choice of open or shorted stub may depend in
practice on a number of factors. A short circuited
stub is less prone to leakage of electromagnetic
radiation and is somewhat easier to realize. On the
other hand, an open circuited stub may be more
practical for certain types of transmission lines, for
example microstrips where one would have to drill
the insulating substrate to short circuit the two
conductors of the line.
Single stub matching

7. Impedance Matching
Parallel stub
Series stub

8. Since the circuit is based on insertion of a parallel stub, it
is more convenient to work with admittances, rather than
impedances.
Single stub matching

10. Single stub matching

11. Single stub matching

12. Single stub matching

13. Notice that in this case the load admittance falls outside
the unitary conductance circle. If one moves from load to
generator on the line, the corresponding chart location
moves from the reference point, in clockwise motion,
according to an angle θ (indicated by the light green arc)
Single stub matching

14. Single stub matching
Because for matching, we need to have

15. Single stub matching

16. Single stub matching

17. Single stub matching

18. Single stub matching

19. Single stub matching

20. Single stub matching

21. Single stub matching

22. Single stub matching

23. Single stub matching

24. Length of short Circuited stub

25. Length of Open circuited stub

26. Length of short Circuited stub

27. Length of Open circuited stub

28. Single stub matching

31. Quarter wave Transformer