1. Radio Frequency Fundamentals (1 September 2006)

2. February 2005Copyright 2005 All Rights Reserved2 l Describe the behavior of RF l Explain the properties of an RF signal l Understand the nature of the intentional Radiator and EIRP Objectives Upon completion of this lecture you will be able to:

3. February 2005Copyright 2005 All Rights Reserved3 l What is RF? l RF Behaviors 4 Reflection 4 Refraction 4 Diffraction 4 Scattering 4 Absorption l Gain and Loss Radio Frequency

4. February 2005Copyright 2005 All Rights Reserved4 l Radio Frequencies are high frequency alternating current (AC) signals that pass along a copper conductor and then radiated into the air via an antenna. l The Antenna 4 Coverts the wired signal into a wireless signal and 4 Converts the wireless signal into a wired signal. l The RF propagates from the antenna in a straight line in all directions. Radio Frequency

5. February 2005Copyright 2005 All Rights Reserved5 Alternating Sine Wave Fundamental Characteristics 1. Amplitude 2. Frequency 3. Phase

6. February 2005Copyright 2005 All Rights Reserved6 l Wavelength = 300,000,000 meters per sec / Frequency in Hz. 4 Length of one wave at a specific frequency. 4 As the frequency increases the wavelength decreases. l A frequency is the number of wavelengths per unit time 1 cycle /second = 1Hz 1,000 cycles/second = 1Khz 1,000,000 cycles /second = 1Mhz 1,000,000,000 cycles/second = 1Ghz Wavelength vs Frequency

7. February 2005Copyright 2005 All Rights Reserved7 Electromagnetic Frequency Spectrum

8. February 2005Copyright 2005 All Rights Reserved8 Wavelength = Speed of Light/Frequency Visible Light Fiber Optic Electromagnetic Spectrum 800 850 1300 1500 Micro = 1 x 10 -6 Nano = 1 x 10 -9 Pico = 1 x 10 -12

9. February 2005Copyright 2005 All Rights Reserved9 l Gain describes an increase in the RF signal's Amplitude. An external source is normally used to amplify the signal. 4 RF Amplifier amplifies the signal while a 4 Directional High-gain antenna focuses the beamwidth to increase the signal amplitude. 4 Reflected signals combined with the main signal can cause gain. RF Behavior

10. February 2005Copyright 2005 All Rights Reserved10 l Loss describes a decrease in signal strength. Loss is caused by such things as: 4 Resistance of cables 4 Resistance in connectors. 4 Impedance mismatch can cause a signal to be reflected back toward the source. 4 Objects such as trees or buildings in the transmission path can cause the signals to be absorbed or reflected. 4 RF Attenuators and accurate resistors convert frequency to heat to reduce the signal amplitude. RF Behavior

11. February 2005Copyright 2005 All Rights Reserved11 l Reflection occurs when a propagating electromagnetic wave impacts an object with dimensions larger than the wavelength of the propagating wave. 4 Reflections can be caused by the earth, buildings, walls, lakes, metal roofs, metal blinds, metal doors, etc. 4 Reflections of the main signal from many objects is referred to as multipath. 4 Multipath can degrade or cancel a signal at the receiver. 4 Antenna diversity is normally used to overcome Multipath. l Refraction describes the bending of radio waves as they pass through a medium of different density. 4 For example, RF waves passing through different density of the atmosphere may change direction away from the receiver. l Absorption occurs when the RF signal strikes an object and is absorbed rather than being reflected, refracted or bent. RF Behavior Contd

12. February 2005Copyright 2005 All Rights Reserved12 Reflection Refraction

13. February 2005Copyright 2005 All Rights Reserved13 LIGHT REFRACTION AIR WATER REFRACTION APPARENT POSITION REAL POSITION 4 Light traveling from one medium to another changes speed. 4 When it changes speed it changes direction of travel. 4 The change in direction is called Refraction. 4 Each object has a Refractive Index (RI).

14. February 2005Copyright 2005 All Rights Reserved14 PRISM REFRACTION RED ORANGE YELLOW GREEN BLUE VIOLET White Light REFRACTION VACUMN1.0300,000 AIR1.00003300,000 WATER1.33225,000 FUSED QUARTZ1.46205,000 GLASS1.5200,000 DIAMOND2.0150,000 SILICON3.4 88,000 GALLIUM ARSINIDE3.6 83,000 MATERIAL INDEX (n) LIGHT VELOCITY (km/s) NOTE: Different frequencies travel at different speeds through the same media.

15. February 2005Copyright 2005 All Rights Reserved15 l Diffraction describes an RF wave bending around an obstacle whereas Refraction describes an RF wave bending through a medium. 4 Diffraction is the slowing of the wave were the wave front strikes the obstacle while the rest of the wave front maintains the same speed of propagation. 4 Scattering occurs when the medium through which the wave travels: 4 Have objects with dimensions that are small compared to the wavelength of the signal and 4 The number of obstacles per area is large. 4 Scattering can occur * First, when the wave strikes an uneven object such as sand, rocks, etc., and is reflected in many different directions. * Second, when a signal wave travels through air particles such as dust, smog, rain, etc. RF Behavior Contd

16. February 2005Copyright 2005 All Rights Reserved16 Diffraction Scattering

17. February 2005Copyright 2005 All Rights Reserved17 l What is VSWR? l Causes of VSWR l Effects of VSWR 4 Decreased signal amplitude 4 Transmitter and amplifier failure Voltage Standing Wave Ratio (VSWR)

18. February 2005Copyright 2005 All Rights Reserved18 Voltage Standing Wave Ratio (VSWR) l VSWR occurs when there is a mismatched impedance between devices in an RF signal. 4 For example, if the cable leading to the antenna is 50 ohms and the connector to the antenna is 75 ohms then an impedance mismatch has occurred. * Some power will be reflected back toward the transmitter by the mismatched connector. * Maximum power will not be transmitted to the antenna. l VSWR is expressed as a ratio between two numbers, i.e. the ratio of the impedance mismatch to a perfect impedance. 4 A VSWR of 1:1 denotes a perfect match whereas 4 A VSWR of 1.5:1 expresses an impedance mismatch.

19. February 2005Copyright 2005 All Rights Reserved19 VSWR Contd l VSWR can cause: 4 A decrease in amplitude of the transmitted signal and 4 Electronics circuitry burning out due to reflected power. l VSWR can be prevented by: 4Making sure there is no impedance mismatch. * Using only 50 Ohm devices in a wireless system. 4 Tight connections on all equipment 4 High-quality equipment

20. February 2005Copyright 2005 All Rights Reserved20 4 Line of sight (LOS)? 4 Fresnel Zones 4 Obstructions 4 Antenna Gain 4 Intentional Radiator 4 Equivalent Isotropically Radiated Power (EIRP) Antenna Principles)

21. February 2005Copyright 2005 All Rights Reserved21 l A Transmitting antenna converts electrical energy into RF waves l Receiving antenna convert RF waves into electrical energy l The physical Dimension of an Antenna are directly related to the transmitting or receiving frequency. 4 The higher the frequency the smaller the transmitter/receiver. Antenna Principles

22. February 2005Copyright 2005 All Rights Reserved22 External Antenna Classifications l Omnidirectional Antenna 4 Mast mount omni 4 Pillar mount omni 4 Ground plane omni 4 Ceiling mount omni l Highly Directional Antenna 4 Parabolic dish 4 Grid antenna l Semidirectional Antenna 4 Patch Antenna 4 Panel Antenna 4 Sectorized antenna 4 Yagi Antenna http://www.fab-corp.com

23. February 2005Copyright 2005 All Rights Reserved23 External Antenna Contd 2.4 Gz 6 dB Log Periodic Antenna 2.4 Gz 5 dB Magnetic Mount Omni Antenna

24. February 2005Copyright 2005 All Rights Reserved24 2.4 Gz 10 dBi Omni-Directional Antenna

25. February 2005Copyright 2005 All Rights Reserved25 15.5 dBi Flat Panel Panel (6 – 90 degree beamwidth)

26. February 2005Copyright 2005 All Rights Reserved26 Circular Yagi Antenna

27. February 2005Copyright 2005 All Rights Reserved27 Directional Yagi Antenna

28. February 2005Copyright 2005 All Rights Reserved28 External Antennas 2.4 Gz 14 dBi Radome Yagi Antenna 2.4 Gz 19 dBi Reflector Grid Antenna

29. February 2005Copyright 2005 All Rights Reserved29 Antenna Gain l The Antenna is a passive device that cannot amplify, filter or shape the signal. l The antenna, however, can create the effect of amplification by focusing the RF radiation into a small beam. 4The radiation is measured by the beamwidth in terms of horizontal or vertical degrees. * An OmniDirectional has a beamwidth of 360 degrees. Whereas * The Yagi may have a beamwidth of 30 degrees. l A tightly focused beam (highly directional antenna) will maximize the propagated wave at low power.

30. February 2005Copyright 2005 All Rights Reserved30 Intentional Radiator l The intentional radiator (IR) includes the RF device and all cabling and connectors up to but not including the antenna. 4 Any reference to power output of the IR refers to the power output at the last cable or connector before the antenna. 4 For example, a transmitter with 30 mw of power might lose 15 mw in the cable, 5 mw in the connector leaving only 10 mw at the IR. 4 It is the responsibility of the WLAN Administrator to manage power output.

31. February 2005Copyright 2005 All Rights Reserved31 Equivalent isotropically Radiated Power (EIRP) l EIRP is the power radiated by the antenna and takes into account the gain of the antenna. 4 For example, if an antenna had a gain of 10 dBi and was fed by 100 mw of power then the EIRP would be 1000 mW or 1 watt of radiated power. 4 It is the responsibility of the WLAN Administrator to assure she is in conformance with FCC power output regulations and that she has properly calculated a viable link.

32. February 2005Copyright 2005 All Rights Reserved32 End of Lecture