This document discusses radio frequency (RF) concepts including: - RF refers to electromagnetic frequencies between 3 kHz and 300 GHz used in radio and radar. RF currents have special properties like flowing along conductor surfaces (skin effect) and radiating energy as electromagnetic waves. - RF currents can cause burns but often do not cause a painful electric shock sensation due to their high frequency. Their ability to flow through insulating materials like capacitors decreases with increasing frequency. - Factors that impact RF signals include free space loss as signals spread out, skin effect, absorption from the environment, and reflection from objects. Impedance matching is important to minimize signal reflections from impedance mismatches. - Noise is an unwanted signal

1. Radio frequency (RF) is any of the
electromagnetic wave frequencies
that lie in the range extending from
around 3 kHz to 300 GHz, which
include those frequencies used
in radio communication or radar.
What is RF?

2. Special properties of RF current
 Electric currents that oscillate at radio frequencies
have special properties not shared by direct
current or alternating current of lower frequencies.
 Energy from RF currents in conductors can radiate into
space as electromagnetic waves (radio waves). This is
the basis of radio technology.
 RF current does not penetrate deeply into electrical
conductors but tends to flow along their surfaces; this
is known as the skin effect.
Properties of RF.

3. RF currents applied to the
body are harmful, but often do not
cause the painful sensation of electric
shock that lower frequency currents
produce.
This is because the current
changes direction too quickly to trigger
depolarization of nerve membranes.
However they can cause
serious superficial burns called RF
Burns.

4. Another property is the ability to
appear to flow through paths that contain
insulating material, like
the dielectric insulator of a capacitor.
This is because capacitive reactance (Xc) in a
circuit decreases with frequency.
In contrast, RF current can be
blocked by a coil of wire, or even a single
turn or bend in a wire.
This is because the inductive reactance of a
circuit increases with frequency.

5. Electromagnetic Spectrum
SOUND LIGHTRADIO HARMFUL RADIATION
VHF = VERY HIGH FREQUENCY
UHF = ULTRA HIGH FREQUENCY
SHF = SUPER HIGH FREQUENCY
EHF = EXTRA HIGH FREQUENCY
4G CELLULAR
56-100 GHz
2.4 GHz
ISM band
ISM bands
315-915 MHz
UWB
3.1-10.6 GHz

6. Frequency Spectrum
Designation Abbreviation Frequencies Free-space Wavelengths
Very Low Frequency VLF 9 kHz - 30 kHz 33 km - 10 km
Low Frequency LF 30 kHz - 300 kHz 10 km - 1 km
Medium Frequency MF 300 kHz - 3 MHz 1 km - 100 m
High Frequency HF 3 MHz - 30 MHz 100 m - 10 m
Very High Frequency VHF 30 MHz - 300 MHz 10 m - 1 m
Ultra High Frequency UHF 300 MHz - 3 GHz 1 m - 100 mm
Super High Frequency SHF 3 GHz - 30 GHz 100 mm - 10 mm
Extremely High Frequency EHF 30 GHz - 300 GHz 10 mm - 1 mm

8. Regulations ISM/SRD Bands

9. TRANSMITTERS AND
RECEIVERS

10. TRANSMITTERS AND RECEIVERS
 An Interesting Thing To Know
 An electrical signal can move from place to
place two different ways:
1) As current on a conductor (e.g. a wire)
2) As invisible waves in the air.

11. Antenna - How it Works…...!
The antenna converts radio frequency electrical energy fed to it (via
the transmission line) to an electromagnetic wave propagated into
space.
The physical size of the radiating element is proportional to the
wavelength. The higher the frequency, the smaller the antenna size.
Assuming that the operating frequency in both cases is the same,
the antenna will perform identically in Transmit or Receive mode

12. As a current on conductor……

14. As a invisible wave in air…..

15. An antennas polarization is relative to the E-field of antenna.
– If the E-field is horizontal, than the antenna is Horizontally
Polarized.
– If the E-field is vertical, than the antenna is Vertically Polarized.
Polarization
No matter what polarity you choose, all antennas in the same RF
network must be polarized identically regardless of the antenna
type.

16. e.g. Vertically Polarized Antenna

17. Antenna Radiation Patterns
Common parameters
– main lobe (boresight)
– half-power beamwidth (HPBW)
– front-back ratio (F/B)
– pattern nulls
Typically measured in two planes:
• Vector electric field referred to E-field
• Vector magnetic field referred to H-field

18. Pattern : Isotropic Antenna

20. Transmitters & Receivers
 Wireless Communications

21. Transmitters & Receivers
 Wireless Communications

22. Transmitters & Receivers
 Wireless Communications
Transceiver

23. RF Power Definitions
• dBm – power referred to 1 mW
PdBm=10log(P/1mW)
0dBm = 1mW
20 dBm = 100mW
30 dBm = 1W
Example:
-110dBm = 1E-11mW = 0.00001nW
Power = V2/R:
50 W load : -110dBm is 0.7uV
• Rule of thumb:
6dB increase => twice the range
3dB increase => roughly doubles the dbm
power

24. 2. RF Behavior
Loss & Gain
 Decibels
 Bandwidth
 RF in the Environment
 Match

25. Devices
 Two Types Power Supply
Gain
Loss
Heat
Heat

26. Loss & Gain
 Vocabulary
 Gain: Also called amplification & power gain
 Loss: Also called insertion loss & attenuation

27. 2. RF Behavior
 Loss & Gain
Decibels
 RF in the Environment
 Match

28. Decibels
 What's The Problem?
1000 Watts 0.000000000001 Watts

29. Decibels
 The Basics
 Measure a change (e.g. output vs. input)
 Bigger (i.e, gain), decibels are positive
 Smaller (i.e., loss) , decibels are negative
 Decibels are abbreviated "dB"

30. Decibels
 The Only Math You'll Need To Know
 +3dB means 2 times bigger
 +10 dB means 10 times bigger
 -3dB means 2 times smaller
 -10 dB means 10 times smaller
 For every 3 dB gain/loss you will either double your power
(gain) or lose half your power (loss).

31. RF Behavior - Decibels
Decibel Conversion
 Examples
Change Factors Decibels
4000 2 x 2 x 10 x 10 x 10 3+3+10+10+10=36 dB
-4000 -36 dB
5000 10 x 10 x 10 x 10  2 10+10+10+10-3=37 dB
8000 2 x 4000 36 dB + 3 dB = 39 dB
6000 37.5 dB  37. 78 dB

32. dBm
 What Is It?
 A measure of power NOT change
 In The RF World
 The "standard" unit of power is 1 milliwatt
 Definition
 dBm = "dB above 1 milliwatt"

33. dBm
 Example
Gain of device = 30 dB
"Change" Output of device = 30 dBm
"Power"
Output = 30 dB above 1 milliwatt = 30 dBm

34. dBm Conversion

35. dBm to Watt
• About dBm and W
– Voltage Ratio aV = 20 log (P2/P1) [aV] = dB
– Power Ratio aP = 10 log (P2/P1) [aP] = dB
– Voltage Level V‘ = 20 log (V/1µV) [V‘] = dBµV
– Power Level P‘ = 10 log (P/1mW) [P‘] = dBm
• Example: 25mW is the maximum allowed radiated
(transmitted) power in the EU SRD band
– P‘ = 10 log (25mW/1mW) = 10 * 1.39794 dBm ~ 14 dBm

36. dBm Typicals

37. RF In The Environment
Free Space Loss
 Skin Effect
 Absorption
 Reflection

38. Free Space Loss
RF signals spread out as they travel through the air
Power density: Watts per square meter

39. Free Space Loss (FSL)
 Formula
FSL = A function of frequency & distance
FSL > 120 dB

40. Free Space Loss
1000 Watts

41. Free Space Loss
60 dBm
Free Space Loss = 120 dB

42. Free Space Loss
60 dBm
Free Space Loss = 120 dB
- 60 dBm

43. Free Space Loss
60 dBm
-120 dB

44. Free Space Loss
60 dBm
-120 dB
- 60 dBm

45.  Reflection
– incident wave propagates away from smooth
scattering plane
– multipath fading is when secondary waves arrive
out-of-phase with the incident wave causing signal
degradation
Free Space Loss :

46. 2. Refraction
– incident wave propagates through scattering plane but at an
angle
– frequencies less than 10 GHz are not affected by heavy
rains, snow, “pea-soup” fog
– at 2.4 GHz, attenuation is 0.01 dB/Km for 150mm/hr of
rain
3. Diffraction
– incident wave passes around obstruction into shadow regions

47. RF In The Environment
 Free Space Loss
Skin Effect
 Absorption
 Reflection

48. Skin Effect
 What Is It?
 When an RF signal is on a conductor, it resides only on the
surface
Signal on the surface
No signal inside

49. Skin Effect
What Is The Implication?
 RF current does not penetrate deeply into electrical
conductors but tends to flow along their surfaces; this is
known as the skin effect.
 Metal can be used to control airborne RF waves

50. RF In The Environment
 Free Space Loss
 Skin Effect
Absorption
 Reflection

51. Absorption
 What Is It?
 When RF waves travel through the air, some things they
encounter cause attenuation
 Air
 Rain
 Foliage

52. Absorption
 And
 Absorbed energy gets converted to heat
Heat

53. Absorption
 Look Familiar?
Heat

54. Absorption
 What Else?
 Also called atmospheric attenuation
 Measured in dB
Heat

55.  Atmospheric
 Attenuation

56. Absorption
Output Power
Absorption
Free Space Loss

57. RF In The Environment
 Free Space Loss
 Skin Effect
 Absorption
Reflection

58. Reflection
 What Is It?
 When RF waves travel through the air, some things they
encounter cause the signal to be reflected
 Buildings
 Mountains
 Automobiles

59. Reflection
 In Fact
 Some materials reflect the RF completely
 Metal
 Some reflect the RF only partially
 Wood
 Concrete

60. Reflection
 What Does Than Mean?
 Some materials absorb AND reflect RF waves

61. Reflection & Absorption
 Visual Depiction
Incident wave
Reflected wave
Transmitted wave
Heat

62. Summary:
Free space loss Due to signal spreading out
Skin effect Signal on surface of conductor
Absorption Due to the environment
Reflection Signal direction changes

63. 2. RF Behavior
 Loss & Gain
 Decibels
 Bandwidth
 RF in the Environment
Match

64. Match
 Impedance
 Components have impedance
 Conductors have impedance
 Conductors connect components

65. Match
 Impedance
 Components & conductors should have the same impedance
 50 ohms
 But they don't
 Their impedances
don't "match"

66. Match
 Why Don't Things Match?
 Different standards
 50 ohms in the RF world
 75 ohms in the video world
 Impedance varies
 Over frequency
 From unit to unit

67. Mismatch
 What Are The Consequences?
 The RF signal gets reflected
 The bigger the mismatch, the greater the reflection
 If too much signal gets reflected
 Adverse effects

68. Mismatch
Incident signal
Poor match
Incident signal
Reflected signal
Reflected signal
Good match

69. Return Loss
 Meaning
 "The loss that the return (reflected) signal experiences"
 Big RL = small reflected signal
 Small RL = big reflected signal
 Measured in dB
 Just like insertion loss
Good
Bad

70. Return Loss
Incident signal
Poor match
Incident signal
Reflected signal
Reflected signal
Good match
High RL
Low RL

71. Mismatch
 How To Deal With Mismatch
 If the mismatch is small
 Do nothing
 If the mismatch is large
 Impedance matching circuit

72. Impedance Matching:
A proper Impedance Match is essential for maximum
power transfer.
75 ohms 50 ohms
Impedance matching circuit

73. Noise
 What Is It?
 Signal disturbance
 Unwanted signal(s), also called interference
 Where Does It Come From?
 Environment
 Man made

74. Noise
 Types
 AM: Unwanted changes to the amplitude
 Predominantly environment
 FM: Unwanted changes to the frequency
 Predominantly hardware
 PM: Unwanted changes to the phase
 Predominantly hardware

75. Noise
 A Function Of Bandwidth & Temperature
 Noise density
 "Noise floor”
 Thermal noise
-120 dBm

76. Signal To Noise Ratio (S/N)
 Definition
 A measure (in dB) of how much bigger the received
signal is relative to the noise floor
 AM: 40-50 dB
 FM: 20-30 dB
 Digital: 10-20 dB
Receiver sensitivity

77. Link Budget
Noise floor -120 dBm
Power out 40 dBm
Free space loss
-80 dBm
120 dB
Absorption
-90 dBm
10 dB
30 dBS/N

78.  Noise Spectrum Signal Spectrum

79. Thank You…
PATANKAR DIGVIJAY V.
Electromagnetic Engineer.