Lecture 2 - RF Fundamentals
Radio Frequency Fundamentals (1 September 2006) Objectives Upon completion of this lecture you will be able to: q Describe the behavior of RF q Explain the properties of an RF signal q Understand the nature of the intentional Radiator and EIRP February 2005 Copyright 2005 All Rights Reserved Radio Frequency q What is RF? q RF Behaviors Reflection Refraction Diffraction Scattering Absorption q Gain and Loss February 2005 Copyright 2005 All Rights Reserved Radio Frequency q Radio Frequencies are high frequency alternating current (AC) signals that pass along a copper conductor and then radiated into the air via an antenna q The Antenna Coverts the wired signal into a wireless signal and Converts the wireless signal into a wired signal q The RF propagates from the antenna in a straight line in all directions February 2005 Copyright 2005 All Rights Reserved Alternating Sine Wave February 2005 Fundamental Characteristics Amplitude Frequency Phase Copyright 2005 All Rights Reserved Wavelength vs Frequency qWavelength = 300,000,000 meters per sec/Frequency in Hz Length of one wave at a specific frequency As the frequency increases the wavelength decreases qA frequency is the number of wavelengths per unit time cycle /second = 1Hz 1,000 cycles/second = 1Khz 1,000,000 cycles /second = 1Mhz 1,000,000,000 cycles/second = 1Ghz February 2005 Copyright 2005 All Rights Reserved Electromagnetic Frequency Spectrum February 2005 Copyright 2005 All Rights Reserved Electromagnetic Spectrum -6 Micro = x 10-9 Nano = x 10 Pico = x 10-12 Visible Light 800 850 Fiber Optic 1300 1500 Wavelength = Speed of Light/Frequency February 2005 Copyright 2005 All Rights Reserved RF Behavior q Gain describes an increase in the RF signal's Amplitude An external source is normally used to amplify the signal RF Amplifier amplifies the signal while a Directional High-gain antenna focuses the beamwidth to increase the signal amplitude Reflected signals combined with the main signal can cause gain February 2005 Copyright 2005 All Rights Reserved RF Behavior q Loss describes a decrease in signal strength Loss is caused by such things as: Resistance of cables Resistance in connectors Impedance mismatch can cause a signal to be reflected back toward the source Objects such as trees or buildings in the transmission path can cause the signals to be absorbed or reflected RF Attenuators and accurate resistors convert frequency to heat to reduce the signal amplitude February 2005 Copyright 2005 All Rights Reserved 10 Voltage Standing Wave Ratio (VSWR) q VSWR occurs when there is a mismatched impedance between devices in an RF signal 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 q VSWR is expressed as a ratio between two numbers, i.e the ratio of the impedance mismatch to a perfect impedance A VSWR of 1:1 denotes a perfect match whereas A VSWR of 1.5:1 expresses an impedance mismatch February 2005 Copyright 2005 All Rights Reserved 18 VSWR Contd q VSWR can cause: A decrease in amplitude of the transmitted signal and Electronics circuitry burning out due to reflected power q VSWR can be prevented by: Making sure there is no impedance mismatch Using only 50 Ohm devices in a wireless system Tight connections on all equipment High-quality equipment February 2005 Copyright 2005 All Rights Reserved 19 Antenna Principles) Line of sight (LOS)? Fresnel Zones Obstructions Antenna Gain Intentional Radiator Equivalent Isotropically Radiated Power (EIRP) February 2005 Copyright 2005 All Rights Reserved 20 Antenna Principles q A Transmitting antenna converts electrical energy into RF waves q Receiving antenna convert RF waves into electrical energy q The physical Dimension of an Antenna are directly related to the transmitting or receiving frequency The higher the frequency the smaller the transmitter/receiver February 2005 Copyright 2005 All Rights Reserved 21 External Antenna Classifications q Omnidirectional Antenna q Semidirectional Antenna Mast mount omni Patch Antenna Pillar mount omni Panel Antenna Ground plane omni Sectorized antenna Ceiling mount omni Yagi Antenna q Highly Directional Antenna Parabolic dish Grid antenna http://www.fab-corp.com February 2005 Copyright 2005 All Rights Reserved 22 External Antenna Contd 2.4 Gz dB Log Periodic Antenna 2.4 Gz dB Magnetic Mount Omni Antenna February 2005 Copyright 2005 All Rights Reserved 23 2.4 Gz 10 dBi Omni-Directional Antenna February 2005 Copyright 2005 All Rights Reserved 24 15.5 dBi Flat Panel Panel (6 – 90 degree beamwidth) February 2005 Copyright 2005 All Rights Reserved 25 Circular Yagi Antenna February 2005 Copyright 2005 All Rights Reserved 26 Directional Yagi Antenna February 2005 Copyright 2005 All Rights Reserved 27 External Antennas 2.4 Gz 14 dBi Radome Yagi Antenna 2.4 Gz 19 dBi Reflector Grid Antenna February 2005 Copyright 2005 All Rights Reserved 28 Antenna Gain q The Antenna is a passive device that cannot amplify, filter or shape the signal q The antenna, however, can create the effect of amplification by focusing the RF radiation into a small beam The 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 q A tightly focused beam (highly directional antenna) will maximize the propagated wave at low power February 2005 Copyright 2005 All Rights Reserved 29 Intentional Radiator q The intentional radiator (IR) includes the RF device and all cabling and connectors up to but not including the antenna Any reference to power output of the IR refers to the power output at the last cable or connector before the antenna For example, a transmitter with 30 mw of power might lose 15 mw in the cable, mw in the connector leaving only 10 mw at the IR It is the responsibility of the WLAN Administrator to manage power output February 2005 Copyright 2005 All Rights Reserved 30 Equivalent isotropically Radiated Power (EIRP) q EIRP is the power radiated by the antenna and takes into account the gain of the antenna 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 watt of radiated power 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 February 2005 Copyright 2005 All Rights Reserved 31 End of Lecture February 2005 Copyright 2005 All Rights Reserved 32 ... http://www.fab-corp.com February 20 05 Copyright 20 05 All Rights Reserved 22 External Antenna Contd 2. 4 Gz dB Log Periodic Antenna 2. 4 Gz dB Magnetic Mount Omni Antenna February 20 05 Copyright 20 05 All... ARSINIDE February 20 05 LIGHT VELOCITY (km/s) 1.0 1.00003 1.33 1.46 1.5 2. 0 3.4 3.6 Copyright 20 05 All Rights Reserved 300,000 300,000 22 5,000 20 5,000 20 0,000 150,000 88,000 83,000 14 RF Behavior Contd... Rights Reserved 23 2. 4 Gz 10 dBi Omni-Directional Antenna February 20 05 Copyright 20 05 All Rights Reserved 24 15.5 dBi Flat Panel Panel (6 – 90 degree beamwidth) February 20 05 Copyright 20 05 All Rights