Fundamental of Radio Frequency

Fundamental of Radio frequency and its fundamental concepts.
Electromagnetic Spectrum

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 LIGHT RADIO 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

7. Regulations ISM/SRD Bands

8. TRANSMITTERS AND RECEIVERS

9. 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.

10. 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

11. As a current on conductor……

12. As a invisible wave in air…..

13. 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.

14. e.g. Vertically Polarized Antenna

15. 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

16. Pattern : Isotropic Antenna

17. Transmitters & Receivers Wireless Communications

18. Transmitters & Receivers Wireless Communications

19. Transmitters & Receivers Wireless Communications Transceiver

20. RF Power Definitions dBm – power referred to 1 mW P dBm =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

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

22. Devices Two Types Power Supply Gain Loss Heat Heat

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

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

25. Decibels What's The Problem? 1000 Watts 0.000000000001 Watts

26. 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"

27. 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).

28. RF Behavior - Decibels Decibel Conversion Examples

29. 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"

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

31. dBm Conversion

32. 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

33. dBm Typicals

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

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

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

37. Free Space Loss 1000 Watts

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

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

40. Free Space Loss 60 dBm -120 dB

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

42. 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 :

43. 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

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

45. 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

46. 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

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

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

49. Absorption And Absorbed energy gets converted to heat Heat

50. Absorption Look Familiar? Heat

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

52. Atmospheric Attenuation

53. Absorption Output Power Absorption Free Space Loss

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

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

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

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

58. Reflection & Absorption Visual Depiction Incident wave Reflected wave Transmitted wave Heat

59. Summary:

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

61. Match Impedance Components have impedance Conductors have impedance Conductors connect components

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

63. 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

64. 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

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

66. 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

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

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

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

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

71. 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

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

73. 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

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

75. Noise Spectrum Signal Spectrum

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