1. RF and Microwave Basics

2. RF and Microwave Basics
Objective:
To familiarize test engineers with various terms and
definitions related to testing RF and microwave
components. To define common tests performed on these devices and show some common test programs which use this information.

3. RF and Microwave Basics
What is RF ( Radio Frequency )?
RF is defined as a frequency range within which
radio waves may be transmitted, from about 10KHz
to 300MHz.
What is Microwave ?
The term Microwave Frequencies is generally used
for those wavelengths measured in centimeters,
roughly from 30 cm to 1 mm. ( 1 to 300GHz )

5. RF and Microwave Basics

6. RF and Microwave Basics

7. RF and Microwave Basics
What is a transmission line ?
The term transmission line means a media by which a
signal or power transferred from one point to another.
Two conductors form a transmission line. Between these
two conductors E and H fields are formed. There are
several types of transmission lines, these include:
microstrip stripline
coax twin-lead
slotline waveguide

8. RF and Microwave Basics

9. RF material
Waveguide
Coaxial cable
MicroStrip Line

10. RF and Microwave Basics

11. RF and Microwave Basics

12. RF and Microwave Basics
At lower frequencies, V and I can be considered equal at all points along the transmission line since the wavelength is much greater than the length of the transmission line. With respect to frequencies in the RF and Microwave bands, the reactive characteristics ( L,C ) of the trans-mission line model will dominate the voltage and current along the transmission line.
This is referred to as“Traveling Waves” and at higher
frequencies special considerations must be made.

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16. RF and Microwave Basics
The same concept is applied to Energy traveling on Transmission
lines. If a transmission line is not terminated in the matching Zo,
some of the incident energy is reflected back towards the source
causing a standing wave.
This reflected energy can be measured and the exact value of the load can be determined. The ratio of the reflected to incident energy is referred to as Gamma or the reflection coefficient. Gamma is a vector with both real and imaginary components.

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18. RF and Microwave Basics

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25. RF and Microwave Basics

26. RF and Microwave Basics

27. Scattering Parameter (S-parameter)

28. RF and Microwave Basics

29. RF and Microwave Basics
Units of Measure:
Decibel (dB)
The Decibel is a logarithmic unit of measure originated
to quantify sound loudness. The use of dB allows for
a wider range of values on a smaller scale and simplifies
mathematics by replacing multiplication and division
with addition and subtraction.
dBm
Most microwave measurements are power measure-
ments dBm is a reference to 1.0 mW and is used in 50
Ohms measurement systems.

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31. RF and Microwave Basics

32. RF and Microwave Basics

34. Smith Charts Why do we use Smith Charts for?
Why do we use Smith Charts for?
- To help us solve lengthy complex equations graphically on the chart.
- To reduce the possible errors encountered during manual calculations.
- Helps to match a given source to a specified load using graphical approach.
Smith Chart is one of the most useful graphical tools available to a RF circuit designer. It is developed in the 1930s by a Bell Lab engineer by the name of Philip Smith.
The Smith chart is used to reduce the “pain” of a RF circuit designer in solving lengthy complex equations and hence reducing the number of possible errors in calculation.
We do not need to know or understand the mathematics behind the construction of a Smith chart (although it is better to understand too) as long as we understand what the chart represents and how we can use it to our advantage.
There are many uses for the chart, but we will concentrate mainly on the Smith Chart as an impedance matching tool.
We will learn about the various components of a Smith Chart and how we can use the Smith Chart to match a given source to a specified load.
The concept of matching will be further illustrated in a later slide.

35. Smith Charts How do we interpret a Smith Chart?
Components of the Smith Chart:
- A family of circles - Constant resistance circles.
- A family of arc of circles - Constant reactance circles.
The Smith Chart is basically a combination of a family of circles and a family of arc of circles.
The family of circles (from small radii to large radii) are known as constant resistance circles. Each point on a constant resistance circle has the same resistance as any other point on the circle.
The family of arc of circles are known as constant reactance circles. Each point on the arc of circle has the same reactance as any other point on the arc. The center of these circles are centered off the chart.

36. Constant resistance circles
0.1
1.2
4.0
2.0
1.0
0.6
0.3
10.0
The outer boundary of the chart is defined as the “R=0” circle, with higher values of R as the circles approaches the right hand side of the chart.
Hence when we draw a horizontal centerline across the circle “R=0”, the point on the right hand side of the line would represent a point of infinite resistance, which represents an open circuit.
The point on the left most end of the line would represent the point where R=0, which represents a short circuit.
Note that this slide and the next slide refers to normalized Smith Charts. Normalization will be covered in a later slide.
Note: Diagram not drawn to scale.

37. Constant reactance circles
X=0
Inductive Reactance
Capacitive Reactance
1.2
0.8 3
0.5
+jX
-jX 10
0.3
0.1
-0.1
-0.3
-10
All arcs above the centerline (X=0) of the chart would represent +jX or inductive reactance and all arcs below the centerline would represent -jX or capacitive reactances.
J=root(-1). So when c=1/j2fC = 1/j2fC *(j/j) =-j(1/ 2fC), hence capacitance is -jX.
The circles shown above have their centres off the chart, hence only a small part of their circle is contained within the perimeter of the chart.
When we combine both the charts into a single chart, we have what is known as a Smith Chart.
-0.5 -3
-0.8
-1.2
Note: Diagram not drawn to scale.

38. Combining the previous 2 charts
We have our Smith Chart!
Any point on the Smith chart will be a combination of resistance and reactance of the form Z=R+jX.
Note: Diagram not drawn to scale.

39. Smith Charts Other components of the Smith Chart:
- Translating impedance to reflection coefficient, .
where Z0 is defined as the characteristic impedance of the transmission medium.

40. Smith Charts
can be represented on the Smith Chart as a polar form, with magnitude and phase.
1800
900
-900 00
0.8
+ Degrees
- Degrees
0.3
Any point on the Smith chart will be a combination of resistance and reactance of the form Z=R+jX.
Clock wise direction is for -ve angle and otherwise.
Note: Diagram not drawn to scale.

41. Smith Charts
The center of the chart will be Z0=50 if the characteristic impedance is based on 50. At this point (Z=50), = 0.
Note: Diagram not drawn to scale.

42. Smith Charts Smith Chart that is not normalized.
Smith Chart that is normalized.
We will denote characteristic impedance as small letter z, while the unnormalized impedance as capital Z.
Z can be ZO , ZL or Zin
Note: Diagram not drawn to scale.

43. Admittance Smith Chart
Smith Charts
Impedance Smith Chart
Admittance Smith Chart
Mirror
Inductive +j
Inductive -j
The admittance smith chart shown above is a modified admittance smith chart that is developed by reflecting the entire impedance chart.
In addition, we can also use the Impedance smith chart to interpret admittance components. This means that the top of the impedance smith chart can be interpreted to be both the inductive as well as the capacitive terminations. However this method is more outdated and more confusing to use.
Capacitive -j
Capacitive +j
The Admittance Smith Chart is a mirror image of the Impedance Smith Chart.
Note: Diagram not drawn to scale.

44. Smith Charts
The admittance Smith Chart will take on the following parameters:
Where Y represents the admittance and it contains both real and imaginary parts.
G is the conductance in mhos and
B is the susceptance in mhos.
Note: Diagram not drawn to scale.

45. Adding a Series Capacitor
Smith Charts
0.6
1.2j
Manipulating impedance on the Smith Chart
1.2
Adding a Series Capacitor
By moving downwards along the constant resistance circle in an counter-clockwise direction, we are adding a series capacitive reactance of -2j ohm to the original RL circuit of j. The resulting circuit is a RC circuit.
0.6
0.9
1.2j
0.6
-2.0j
0.6
-0.8j
-0.8
Note: Diagram not drawn to scale.

46. Adding a Series Inductor
Smith Charts
0.6
1.2j
Manipulating impedance on the Smith Chart
0.6
-0.8j
+2j
1.2
Adding a Series Inductor
By moving upwards along the constant resistance circle in an clockwise direction, we are adding a series inductive reactance of +2j ohm to the original RC circuit of j. The resulting circuit is a RL circuit.
0.6
0.9
0.6
-0.8j
-0.8
Note: Diagram not drawn to scale.

47. Adding a Parallel Capacitor
Smith Charts
Manipulating impedance on the Smith Chart
-0.5j
0.1
-0.5
+0.5
0.1
Adding a Parallel Capacitor
By moving downwards along the constant resistance circle in an clockwise direction, we are adding a parallel capacitive reactance of +1j ohm to the original RL parallel circuit of j. The resulting circuit is a RC parallel circuit.
Note that this is a Admittance Smith Chart.
+0.5j
0.1
-0.5j
0.1
+1j
Note: Diagram not drawn to scale.

48. Adding a Parallel Inductor
Smith Charts
-0.5j
0.1
0.1
-1j
Manipulating impedance on the Smith Chart
+0.5j
Adding a Parallel Inductor
-0.5
By moving upwards along the constant resistance circle in an counter-clockwise direction, we are adding a parallel inductive reactance of -1j ohm to the original RL parallel circuit of j. The resulting circuit is a RL parallel circuit.
Note that this is a Admittance Smith Chart.
0.1
+0.5
+0.5j
0.1

49. Can we do a quick summary!
Smith Charts
Can we do a quick summary!
Inductive +j
Moving in an anti-clockwise direction, we add series capacitance (-jX).
Moving in a clockwise direction, we add series inductance (+jX).
Capacitive -j
Impedance Smith Chart
Note: Diagram not drawn to scale.

50. Smith Charts Inductive -j
Inductive -j
Moving in a clockwise direction, we add parallel capacitance (+jX).
Moving in an anti-clockwise direction, we add parallel inductance (-jX).
Capacitive +j
Admittance Smith Chart
Note: Diagram not drawn to scale.

52. Smith Charts
Teradyne Smith Chart Display

53. Common Device Tested in ATE
RF Mixers, Synthesizers, LNAs, and Prescalars (900MHz & 1.9 GHz)
Wireless LAN Chipset (2.4GHz)
GSM IQ Transceiver (900MHz)
Prescaler/Charge Pump (900Mhz & 1.9GHz)
DECT Chipset (1.9GHz)
LNA/Mixer/VCO (900MHz)
Modulation Synthesizer
Single chip RFID (2.4GHz)
GPS Chipset (1.6GHz)
IQ Modulator/Demodulator w/Digital BaseBand
DECT = Digital Electronic Cordless Telephone
IQ = In=phase quadrature
GPS = Global position system

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60. RF System