1. 12
Transmission Lines

2. Types of Transmission Lines
Two-Wire Open Line
Transmission line between antenna and transmitter or antenna and receiver.
Simple construction.
Twisted Pair
Two insulated wires twisted to form flexible line without use of spacers.

3. Types of Transmission Lines
Unshielded Twisted Pair (UTP)
Used for computer networking; CAT6 and CAT5e.
See Table 12-1: T568A/T568B Wiring

4. Table T568A/T568B Wiring

5. Types of Transmission Lines
Unshielded Twisted Pair (UTP)
Used for computer networking; CAT6 and CAT5e.
See Table 12-2: Different Categories for Twisted-Pair Cable

6. Table 12-2 Different Categories for Twisted-Pair Cabl3

7. Types of Transmission Lines
Shielded Pair
Parallel conductors separated from each other, and surrounded by solid dielectric.

8. Types of Transmission Lines
Coaxial Lines
Rigid or air; flexible or solid.
Balanced/Unbalanced Lines
Unbalanced
Amplitude of electrical signal by center conductor in coaxial line measured with respect to grounded outer conductor.
Balanced
Same current flows in each wire but 180° out of phase.

9. Electrical Characteristics of Transmission Lines
Two-Wire Transmission Line
Electrical characteristics
Construction of line.
Characteristic Impedance
Impedance measured at any point on line would be the same.

10. Electrical Characteristics of Transmission Lines
Transmission Line Losses
Copper
Dielectric
Radiation or induction

11. Propagation of DC Voltage Down a Line
Physical Explanation of Propagation
To understand characteristics of transmission line with ac voltage applied, infinitely long transmission line analyzed with dc voltage applied.
Velocity of Propagation
Current moving down the line, its electric and magnetic fields are propagated down the line.

12. Propagation of DC Voltage Down a Line
Delay Line
Delay signal by some specific amount of time.
Wavelength
Distance traveled by wave during a period of one cycle.

13. Nonresonant Line Traveling DC Waves Nonresonant line Traveling waves
Line of infinite length or as one terminated with resistive load equal in ohmic value to characteristic impedance of line.
Traveling waves
Voltage and current waves; move in phase with one another from source to load.

14. Nonresonant Line Traveling AC Waves
Little difference between charging of line when ac voltage applied to it and when dc voltage applied.

15. Resonant Transmission
DC Applied to an Open-Circuited Line
Resonant line
Transmission line terminated with impedance not equal to characteristic impedance.
Because impedances are equal, applied voltage divided equally between source and line.

16. Resonant Transmission
Incident and Reflected Waves
Voltage on open-circuited wire equal to source voltage, and current is zero.

17. Resonant Transmission
DC Applied to a Short-Circuited Line
Voltage reflection from open circuit is in phase, while from short circuit it is out of phase.
Current reflection from open circuit is out of phase, while from short circuit it is in phase.

18. Resonant Transmission
Standing Waves
Open Line
Mismatch
Incident and reflected waves interact.
Standing wave
Remains in one position, varying only in amplitude.

19. Resonant Transmission
Standing Waves
Shorted Line
Out-of-phase reflection that occurs for current on open line and voltage on shorted line.
Impedance
Voltage divided by current.

20. Resonant Transmission
Quarter-Wavelength Sections
Phase inversion of voltage and current every quarter wavelength.
Cavity filter or selective cavity extends idea of quarter-wavelength coaxial stub filter to high-power operation.

21. Standing Wave Ratio Standing Wave Reflections
Instantaneous vector addition of incident-wave amplitude with that of reflected wave as result of impedance mismatch between transmission line and load.
Reflections
Occur when impedance mismatch.

22. Standing Wave Ratio Degree of Mismatch
Reflection coefficient, voltage standing-wave ratio, return loss.

23. Standing Wave Ratio Voltage standing wave ratio (VSWR)
Ratio of maximum voltage to minimum of standing wave on a line.
Standing wave ratio (SWR)
Equal to ratio of maximum current to minimum current.

24. Standing Wave Ratio Effect of Mismatch Flat line
Perfect condition of no reflection when load purely resistive and equal to Z0.
Higher the VSWR, the greater is mismatch on line.

25. Standing Wave Ratio Quarter-Wavelength Transformer Electrical Length
Not physically a transformer; offers property of impedance transformation.
Electrical Length
Line can be miles long physically and electrically short at low frequencies.

26. The Smith Chart Transmission Line Impedance Impedance
Constantly changing along line and equal to ratio of voltage to current at given point.
Smith chart presents solution to impedance-matching problems posed by complex sources and complex loads.

27. The Smith Chart Transmission Line Impedance
Smith chart impedance-matching tool for transmission lines.
Graphical Smith chart used to represent network analyzer solutions.

28. The Smith Chart Smith Chart Normalizing
Dividing all impedances by characteristic impedance of the line.
Reciprocal of impedance defined as admittance and reciprocal of reactance is called susceptance.

29. The Smith Chart Smith Chart
Greatest utility as impedance-matching calculator.
Allows for simple conversion of impedance to admittance, and vice versa.

30. The Smith Chart Smith Chart Spiral
True standing wave representation on Smith chart.
Many calculations with transmission lines pertain to matching load to line and keeping VSWR as low as possible.
Use of short-circuited stubs prevalent in matching problems.

31. Transmission Line Applications
Discrete Circuit Simulation
Transmission line sections: used to simulate inductance, capacitance, LC resonance.
Baluns
Unbalanced-to-balanced transformer.

32. Transmission Line Applications
Transmission Lines as Filters
Quarter-wave section of transmission line used as efficient filter or suppressor of even harmonics.

33. Transmission Line Applications
Slotted Lines
Section of coaxial line with lengthwise slot cut in outer conductor; pickup probe inserted into slot.
VSWR, generator frequency, unknown load impedance.

34. Transmission Line Applications
Time-Domain Reflectometry
Short-duration pulse transmitted into a line.
Monitored with oscilloscope.

35. Impedance Matching and Network Analysis
Network analyzer
Test equipment to characterize linear impedance characteristics of devices under test (DUTs).
Scalar network analyzer
Measures magnitude of DUT impedance.

36. Impedance Matching and Network Analysis
Vector network analyzer (VNA)
Determines impedance magnitude and phase characteristics of DUTs.
Scattering or S-parameters
Linear transmission and reflection characteristics of signals applied to DUTs.

37. Impedance Matching and Network Analysis
Scattering matrix
Describes all voltages incident to and reflected from all ports.
Impedance analysis not confined to microwave systems.

38. Impedance Matching and Network Analysis
Vector network analyzer
System of three receivers and two-port “test set” that separates forward and reflected components of applied signals through directional couplers.