RF Signal & Antenna Concepts PDF

RF Signal & Antenna Concepts Module 5  Module 5: RF Signal and Antenna Concepts  Isotropic radiator  Simple antenna diversity  Passive amplifier Azimuth and Elevation  MIMO antenna diversity  Beamwidth...

RF Signal & Antenna Concepts Module 5  Module 5: RF Signal and Antenna Concepts  Isotropic radiator  Simple antenna diversity  Passive amplifier Azimuth and Elevation  MIMO antenna diversity  Beamwidth  VSWR  Antenna types  Regulatory compliance  Fresnel zone  Mounting  Antenna polarization  Reading assignment: CWNA study guide Module 5 RF Signal and Antenna Concepts Why we need to know about antennas?  To properly select, install, and align antennas  help you successfully implement a wireless network, whether it is a point-to-point network between two buildings or a network providing wireless coverage throughout an office building.  The shape of the antenna radiation pattern determines the application of the antenna Isotropic Radiator  RF transmission of an antenna is usually compared or referenced to an isotropic radiator or a half- wave dipole antenna  Isotropic radiator  a point source that radiates signal equally in all directions.  Examples:  The sun is probably one of the best examples of an isotropic radiator. It generates equal amounts of energy in all directions.  Isotropic antenna – theoretical  Electromagnetic Field Electric and Magnetic fields are perpendicular to one another, moving into space away from the source  Electric Field – E-Plane  Magnetic Field – H-Plane Electric Field Directio n Magnetic Field  The E-field creates an H-field, and vice versa. Together, these two fields create a continuous pattern that move the electromagnetic radiation through space. Electromagnetic Field (Half-dipole Antenna) 𝜆 2 Wavelength for  Passive Amplifier Antenna Radios modulate a baseband signal onto an electrical current Radio RF Cable Transceiv Antennas convert er electrical current into RF waves. The electrical current is carried by a conductive RF cable.  Passive Antenna Gain: dBi and dBd Isotropic Radiator dBi - Decibels relative to an isotropic radiator Half-  Used to measure passive antenna Wave Dipole gain  0 dBi = no directivity / passive gain dBd - Decibels relative to a half-wave dipole  Lesser used unit to measure antenna gain  dBi = dBd + 2.14 dB  0 dBd = 2.14 dBi  Example: Azimuth and Elevation  To assist potential buyers with their purchasing decision, antenna manufacturers create azimuth charts and elevation charts, commonly known as radiation patterns, for their antennas.  These radiation patterns are created in controlled environments, where the results cannot be skewed by outside in influences and represent the signal pattern that is radiated by a particular model of antenna.  These charts are commonly known as polar charts or antenna radiation envelopes.  Azimuth and Elevation Azimuth chart, also known as H-plane, – shows the top-down view of the radiation pattern of the antenna. – For omnidirectional antenna, as you can see from the azimuth chart below, its radiation pattern is almost perfectly circular. The elevation chart, also known as E-plane, shows the side view of the radiation pattern of the antenna. Omnidirectional Antenna Azimuth and Elevation - Illustration  Azimuth and Elevation omnidirectional semidirectional Elevation Azimuth Elevation Azimuth Azimuth chart = H-plane = top-down radiation pattern view Elevation chart = E-plane = side view radiation pattern view The radiation pattern (size) will grow larger or smaller depending on how much power the antenna received, but the shape and the relationships represented by the patterns will always stay the same.  Interpreting Polar Charts  The outer ring of the chart usually represents the strongest signal of the antenna in a given direction.  The chart does not represent distance or any level of power or strength; it represents only the relationship of omnidirectional power between different points on the chart.  The chart is also relative to isotropic antenna or half-wave dipole antenna  Example consider the semi- directional horizontal plane shown: semidirectional  For the semi-directional antenna, if there is a station at 30o azimuth, the signal strength dropped by about -3dB compared to the isotropic antenna  The signal strength at 90o azimuth  Beamwidth  Beamwidth is the measurement of how broad or Main lobe narrow the focus of an antenna is— and is measured both horizontally and vertically. 60o  It is the measurement from the center, or strongest point, of the antenna signal to each of the points along the horizontal and vertical axes, where the Side/back lobes signal decreases by half power (–3 dB).  These –3 dB points are often referred to as half-power points.  The beamwidth in this example is 60o  Antenna Types  There are three major categories of antennas: Omnidirectional, Semi-directional and highly directional  Omnidirectional: Antennas that radiate RF in a fashion similar to the way a table or floor-lamp radiates light. They are designed to provide general coverage horizontally in all directions.  Semidirectional: Antennas that radiate RF in a fashion similar to the way a wall sconce radiates light away from the wall or the way a street lamp shines light down on a street or a parking lot, providing a directional light across a large area.  Highly directional: These highly directional antennas radiate RF in a Different Antenna Beamwidth Horizontal Vertical Antenna Type Beamwidth (in Beamwidth (in Degrees) Degrees) Omnidirectional 360 7 to 80 Patch/panel 30 to 180 6 to 90 Yagi 30 to 78 14 to 64 Sector 60 to 180 7 to 17 Omnidirection Parabolic dish 4 to 25 4 to 21 Parabolic Yag al i Patc Secto h r Omnidirectional High Gain  360º horizontal coverage Low Gain  Vertical coverage varies with gain Omnidirectional  With higher-gain omnidirectional antennas, the vertical signal is decreased, and the horizontal power is increased.  The horizontal beamwidth of omnidirectional antennas is always 360 degrees  The vertical beamwidth ranges from 7 to 80 degrees, depending on the particular antenna.  Because of the narrower vertical coverage of the higher-gain omnidirectional antennas, it is important to carefully plan how they are used  Omnidirectional Usage: – Typically used in point-to-multipoint environments. – Indoor installations typically use low- gain omnidirectional antennas with gain of about 2.14 dBi. – High-gain omnidirectional antennas can also be used outdoors to connect multiple buildings together in a point-to- multipoint configuration.  Semi-directional Used for short-to-medium distance communications – provide a network bridge between two buildings in a campus environment or down the street from each other. – Longer distances would Thebefollowing served bythree highlytypes of antennas fit into thedirectional antennas. semi-directional category: – Patch – Panel – Yagi (pronounced YAH-gee) Horizontal beamwidth < 180 degrees  Semi-directional  Patch antenna  It is common for patch antennas to be connected to access points to provide directional coverage within a building.  Because omnidirectional antennas often have difficulty providing effective RF coverage in areas with shelving.  MIMO patch antennas, such as the one shown, can be used effectively in libraries, warehouses, and retail stores with long aisles of shelves. Extern Interna l  Semi-directional  These antennas can be used for outdoor point-to- point communications up to about a mile  With legacy 802.11/a/b/g radios to help reduce reflections and hopefully reduce the negative effects of multipath.  Semi-directional – Warehouse  Coverage, not capacity, is usually the main concern in a warehouse environment.  The client devices are usually handheld barcode scanners or other wireless data-collection devices that are used for inventory management.  VoWiFi is also common in many warehouse WLAN deployments.  Because most warehouses have very high ceilings, coverage is primarily provided with directional antennas mounted on the walls and pointing down the aisles.  Semi-directional – Warehouse  Because many aisles are very long, directional antennas are often also mounted from the ceiling. This cannot be done with an omnidirectional antenna without causing the signal on the other side of the antenna to be tilted upward.  As shown, the ceiling-mounted directional antennas are mounted in the center of the aisles to provide coverage in combination with the directional antennas mounted on the walls. Semi-directional Another common use case for deploying MIMO patch antennas indoors is in Very High Density (VHD) environments.  The use of directional antennas reduces co-channel interference, especially when a 40 MHz channel reuse pattern is deployed.  Directional antennas are often used in very high-density environments to sector the coverage.  Examples:  Lecture halls, gymnasiums, libraries, cafeterias, etc. Outdoor – Semi-directional  Sector and Yagi antennas  Typically used for short- to medium-distance point-to- point communications of up to about 2 miles, although high- gain Yagi antennas can be used for longer distances.  Outdoor – Highly Directional Root bridge Non-root bridge  Dish and grid antennas  Used strictly for point-to- point bridge links especially for long-distance  They provide the most Parabolic focused, narrow beamwidth Dish of any of the antenna types.  Two types of antennas – Parabolic Dish – Grid Grid  Outdoor – Highly Directional Because of the long distances and narrow beamwidth, highly directional antennas are affected more by antenna wind loading, which is antenna movement or shifting caused by wind. In high-wind environments – grid antennas, because of the spacing between the wires, are less susceptible to wind load and may be a better choice. – Another option in high-wind environments is to choose an antenna with a wider beamwidth. Keep in mind that a wider beam means less gain.  Polarization  Describes the antenna alignment or the orientation of an antenna’s wave oscillations  Determined by the E-field  As waves radiate from an antenna, the amplitude of the waves can oscillate either vertically or horizontally.  Polarization of Tx and Rx antennas should match in Polarization Demo: order to receive the strongest possible signal - Antenna properties ( D2L Week5 folder) ~3 min - Demo with laptop screen in horizontal and vertical position – speedTest - EMANIM  Polarization  Indoor communications  Polarization is not as important because the polarization of the RF signal often changes when it is reflected, which is a common occurrence indoors.  Most access points use low-gain omnidirectional antennas, which should be mounted from the ceiling with vertical polarization.  Laptop manufacturers build antennas into the sides of the monitor. When the laptop monitor is in the upright position, the internal antennas have vertical polarization as well.  Outdoor communication  When you are aligning a point-to-point or point-to-multipoint bridge, proper polarization is extremely important. How many antenna does your smartphone has?  RF Line of Sight Point-to-point RF communication – needs to have an unobstructed line of sight between the two antennas. – make sure that from the installation point of one of the antennas, you have a clear direct path to the other antenna. Unfortunately, for RF communications to work properly, this is not sufficient. – An additional area around the visual LOS needs to remain clear of obstacles and obstructions. This area around the visual LOS is known as the Fresnel zone and is often referred to as RF line of sight.  Simple Antenna Diversity  Exists when wireless device has two antennas and receivers functioning 802.11a/b/g WLAN Radio together Antennas  Legacy APs: 802.11a/b/g use switched antenna diversity to minimize the negative effects of multipath.  When receiving incoming Antenn transmissions, switched diversity a Switch listens with multiple antennas. Multiple antennas Multiple copies of the same signal connected to same radio via arrive at the receiver antennas with a single radio chain different amplitudes.  The signal with the best amplitude is chosen, and the other signals are ignored.  This method of listening for the best  Simple Antenna Diversity 802.11a/b/g WLAN  Switched diversity is also used Radio when transmitting, but only one Antennas antenna is used.  The transmitter will transmit out of the diversity antenna where the best amplitude signal was Antenn last heard. a Switch  The method of transmitting out Multiple antennas connected of the antenna where the last to same radio via a single best-received signal was heard is radio chain known as transmit diversity.  MIMO Antenna Diversity 802.11n/ac MIMO Radio  Multiple-input, multiple-output Antennas (MIMO) is more sophisticated form of antenna diversity that takes advantage of multipath.  MIMO is a wireless radio architecture that can receive or transmit using multiple antennas concurrently.  MIMO Enhances:  Reliability  Range Multiple antennas connected to multiple radio chains  Throughput  Included in 802.11n amendment  Indoor AP and Antenna Mounting Proper installation and connection of the antenna to the wireless transceiver is critical. If the antenna is not properly connected and installed, any benefit that the antenna introduces to the network can be instantly wiped out. Three key components associated with the proper installation of the antenna are – voltage standing wave ratio (VSWR), – signal loss, and – actual mounting of the antenna.  VSWR  Voltage standing wave ratio (VSWR) is a measurement of the change in impedances to an AC signal. 50 Ohms  Voltage standing waves exist because of impedance mismatches or variations between devices in an RF communications system.  When the transmitter generates the AC radio signal, the signal travels along the cable to the antenna. Some of the energy is 75 Ohms reflected back toward the transmitter because of impedance mismatch.  VSWR  VSWR is a ratio measurement of an impedance mismatch:  1:1 (no impedance) being optimal but unobtainable.  Typical values range from 1.1:1 to as 50 Ohms much as 1.5:1.  VSWR military specs are 1.1:1.  Negative effects of VSWR:  Decreased signal amplitude (return loss)  Erratic signal amplitude 75 Ohms  Transmitter or amplifier failure  Signal loss When connecting an antenna: – make sure that as much of the signal that is generated by the transmitter is received by the antenna to be transmitted – pay particular attention to the cables and connectors that connect the transmitter to the antenna. If inferior components are used, or if the components are not installed properly, the access point will most likely function below its optimal capability.  Mounting Antenna Mounting – Placement: AP antennas need placements that are away from reflective surfaces for best performance. Avoid metal support beams, lighting and other obstructions. – Never mount antennas near metal objects as it causes increased multipath and directionality. When possible or practical to do so, always mount the APs as close to the actual users as you reasonable can. Avoid the temptation to hide the AP in crawl spaces or areas that compromise the ability to radiate well. Read manufacturer’s recommendation for mounting detail  Mounting Antenna Mounting (continued) – Indoor mounting considerations Many APs directly installed to metal rail of a drop ceiling Aesthetic and security consideration – Outdoor mounting considerations Mostly mounted on masts or towers with U- bolts Take into consideration wind load – Appropriate use and environment: Does the AP meant for indoor or outdoor use? Ingress Protection Rating (IP Code) National Electrical Manufacturers Association (NEMA) Enclosure Rating "Appareils destinés à être utilisés en ATmosphères Explosives" (ATEX) Directives National Electrical Code (NEC) hazardous locations NEMA Enclosures  The NEMA Enclosure Rating is published by the United States National Electrical Manufacturers Association (NEMA).  NEMA enclosures are often needed to protect outdoor APs from weather conditions.  Many WLAN vendors also manufacture outdoor APs that are already NEMA rated. Questions