132113 Antenna Basics

7/27/2019 132113 Antenna Basics

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Antenna Basics

A guide to effective antenna use

Printed in USA 05/07 P/N 132113

Antennas

Antennas transmit radio signals by converting radio frequencyelectrical currents into electromagnetic waves. Antennas receivethe signals by converting the electromagnetic waves back into radiofrequency electrical currents.

Since electromagnetic waves do not require a medium in which totravel, antennas function in air, space, under water or other liquid,and even through solid matter for limited distances.

Every antenna has specific characteristics that determine thesignals range and radiation pattern or shape. One of the mostimportant characteristics of the antenna is its gain. How theradiation pattern changes with increases in the gain depends on thetype of antenna: omni-directional or directional.

Table of ContentsOverview ....................................................... 1

Anatomy of an Antenna .......... ................... ... 2Gain .............................................................. 3Omni-Directional Antennas ........................... 4

Directional (Yagi) Antennas .................................6Line of Sight .................................................. 7Link Loss Calculations .................................. 7Glossary...................................................... 11


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2 P/N 132113Banner Engineering Corp. Minneapolis, MN U.S.A.

www.bannerengineering.com Tel: 763.544.3164

Anatomy of an Antenna

Antenna element

Ground planeSMA connector

Mounting bracket

Antenna extension cable with an SMA connector at oneend and an N-type male connector at the other end. Thiscable typically connects between the DX80 device and the

antenna or another extension cable.

Antenna extension cable with an N-type male connector atone end and an N-type female connector at the other end.This extension cable typically connects between anothercable and a lightning arrestor or antenna.

Lightning arrestors typically mount between theantenna and the radio system to protect the electricalequipment from damage during a lightning strike.


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P/N 132113 3Banner Engineering Corp. Minneapolis, MN U.S.A.


GainThe antennas gain relates directly to the radio signals radiation pattern and range. Adding gain to a radio system does not amplifythe signal. Antennas with greater gain only focus the signal. A low-gain antenna transmits (and receives) the radio signal equally inall directions. A high-gain antenna transmits its signal farther in one direction than the low-gain system. Antenna gain is measured in

decibels.DecibelsMathematical equations indicate that for every 3 dB increase in the gain, the effective transmission power doubles. Experimentationindicates that for every 6 dB increase in the gain, the radio signal range doubles. Therefore, if a 0 dB antenna (unity gain) transmitsthree miles, a 6 dB antenna on the same radio transmits the signal six miles.

To simplify conversions between dBi, dBm, dBd, use the following approximation:

dBm = dBi = dBd + 2.15

where dBm refers to a ratio of the measured power referenced to 1 milliWatt, dBi is a measurement of an antennas gain compared to amathematically ideal isotropic antenna, and dBd is a ratio of the antennas forward gain to a half-wave dipole antenna.

Why Do You Need GainAccording to rules set by the FCC, radio systems like the DX80 may not exceed 30 dBm Effective Isotopic Radiated Power(EIRP), or

approximately 1 Watt. Since the SureCross radio system has a conducted power of 21 dBm (150 mW), the maximum system gain thatmay be used with the Banner system is 9 dBm. Using higher gain antennas allows users to focus the signal both for transmission andfor reception.

For systems requiring cables and connectors, the losses from the cables and connectors add up to reduce the effective transmissionpower of your radio network. What starts out as a 9 dB antenna may only have an effective gain of 5 dB once losses are totaled. Sincethe 9 dB limit applies to the radio system, including connectors and cables, using a higher gain antenna may be necessary to transmitthe required distance and, using a link loss calculation to account for cabling losses, would still comply with FCC regulations.

In addition to increasing the range, adding gain also changes the radiation pattern. How the radiation pattern changes depends on thetype of antenna: omni-directional or directional.


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The following low-gain, omni-directional antennas are available foruse with the SureCross DX80 wireless radio systems.

Model Number Description

BWA-9O2 Antenna, 900 MHz, Standard, 2 dBi, 360Swivel, 90 Articulation

BWA-2O2 Antenna, 2.4 GHz, Standard, 2 dBi, 360Swivel, 90 Articulation

Omni-Directional Antennas

Antenna

Top View: Low-Gain Dipole Omni

Omni-directional antennas mount vertically and transmit and receiveequally in all directions within the horizontal plane. Omni-directionalantennas are used with the SureCross DX80 Gateway, since theGateway is usually at the center of the standard star topographyradio network.

3 miles

Side View: Low-Gain Dipole Omni

An omni-directional, or omni, antenna transmits and receives radiosignals in the doughnut pattern shown. Note the lack of a signalvery close to the antenna. Most dipole omni antennas have aminimum distance for optimum signal reception. From the top view,the signal radiates equally in all directions from the antenna. Forthis reason, omni-directional antennas are best used for the device

in the center of a star topography network.

6 milesiles66 miles

6dB Gain

Low-Gain

Side View: Dipole Omni Antennas

High GainAn omni antenna with increased gainalso has a circular radiation pattern whenviewed from the top. From the side view,however, the decreased energy sentvertically increases the energy transmittedhorizontally. The radiation pattern stretches

to extend the range, focusing the signalalong a horizontal plane.


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Omni-Directional Antennas (cont)

GATEWAY

NODE

NODE

NODE

Node A

Node C

Node B

Signal A

Signal B

Signal C

Gateways

Signal

With the star topography network, usingthe omni-directional antenna on theGateway ensures that all Nodes fall withinthe antenna radiation pattern.

Low-gain omni-directional antennaswork well in multipath, industrialenvironments. High-gain antennas workwell in line-of-sight conditions.

Part Number Description

BWA-9O5 Antenna, Omni, 896-940 MHz, 5 dBd, 7 dBi

BWA-9O6 Antenna, Omni, 902-928 MHz, 6 dBi

BWA-2O5 Antenna, Omni, 2.4 GHz, 5 dBi, 360 Swivel, 90 Articulation

BWA-2O7 Antenna, Omni, 2.4 GHz, 7 dBi, 360 Swivel, 90 Articulation

The following medium- to high-gain omni-directional antennas are available for use withthe SureCross DX80 wireless radio systems.


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Directional (Yagi) Antennas

A directional, or Yagi, antenna focuses the radio signal in onespecific direction. If you compare antenna radiation patterns to light,an omni antenna radiates a radio signal like a light bulb - evenly

in a spherical pattern. A directional antenna radiates similar to aflashlight - focusing the signal only in one direction. The higher thegain, the more focused the beam becomes.

Low-gain Yagi antenna

NODE

Node A

Node B

GatewaysSignal

GATEWAY

NODE

Yagi antennas are best used in line-of-sight radio systems because Yagisfocus the radio signal in a specific

direction.

In the example to the left, the Gatewayuses an omni antenna to receive radiosignals from multiple directions butthe Nodes use Yagi antennas aimeddirectly at the Gateway to send andreceive the radio signal.

Distance traveled

3 dB Yagi 6 dB Yagi

12 dB Yagi

GATEWAY

NODE

High-Gain YagisBecause Yagi antennas yield narrowerradiation patterns, aiming a high-gain Yagibecomes very important when setting up yourradio network.

The higher the gain of the antenna, the morethe signal is focused along a specific plane.High-gain antennas should only be used forline-of-sight applications.

Part Number Description

BWA-9Y6 Antenna, Yagi, 890-960 MHz, 6.5 dBd

BWA-9Y10 Antenna, Yagi, 890-960 MHz, 10 dBd

The following medium- to high-gain Yagi antennas are available foruse with the SureCross DX80 wireless radio systems.


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Line of Sight

Accurate radio transmission depends on a clear path between radio antennas known as the line of sight. If any obstructions, includingbuildings, trees, or terrain, interrupt the path between antennas, there is no line of sight. Any obstacles interrupting the visual line ofsight will also interfere with the radio signal transmission, resulting in multi-path fade or signal attenuation.

Multi-path fade is the result of radio signals reaching the receiver via two or more paths. In industrial settings, a received signal mayinclude the line of sight signal in addition to signals reflected off buildings, equipment, trees, or outdoor terrain.

Line of sight

Obstruction in the lobe

(Fresnel Zone) of the radio signal.

Despite a clear line of sight, obstructions in the Fresnel zone, a three-dimensional ellipsoid formed with the two antennas as the foci,will still interfere with the radio signal and cause multi-path fade. Raise the antennas high enough to clear any obstructions. Ideally thereshould be no obstructions anywhere in the Fresnel zone, even if line-of-sight is preserved.

If a radio network site is spread over a large area with multiple obstructions or a variety of terrain, conduct a site survey to determineoptimum antenna locations, antenna mounting heights, and recommended gains for reliable performance.

Link Loss Calculations

Link loss calculations determine the exact capabilities of a radio system by calculating the total gain (or loss) of a radio system.

Total Gain = Transmitter gain + Free space loss + Receiver gain

The transmitter and receiver gains are typically positive numbers while the free space loss is a larger negative number. The total gainfor any radio system should be negative. Compare this total gain value to the receiver sensitivity of the Banner SureCross radios listedbelow.

Radio Receivers Rated Sensitivity

900 MHz -104 dBm

2.4 GHz -100 dBm

Item Estimated Loss (dB)

Lightning arrestor 1 dB

N-type connectors (per pair) .5 dB

SMA connector .5 dB

LMR400 coax cable 3.9 dB per 100 ft (0.039 dB per ft)

0.128 dB per meter (1.28 dB per 10 meters

Link loss calculations must include all components of a radio system because any item connected to a radio system has a specific lossassociated with it.

Common items used within a radio network are cables, connectors, and lightning arrestors. Cabling loss is usually measured per foot

while losses for connectors and other items are specific to the component. When calculating the total gain of a radio system, includelosses from all components of the system in your link budget calculations.


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GATEWAY

-0.5 dB

-0.5 dB

-0.5 dB-1 dB

lightning arrestor

(N-type female to N-type male)cable

omni antenna

(6 dBd)Losses:

-0.5 dB per connection-1.0 dB per lightning arrestor

-3.9 dB per 100 ft of cable for LMR400 coax

Reverse polarity SMA connections

N-type female

N-type male

N-type male

N-type female

N-type femaleN-type male -0.5 dB

Item Gain (+)or Loss (-)

DX80 radio* 21 dBi

Connector pairs -1.5 dBi

Lightning arrestor -1 dBi

Cable (50 ft length) -1.95 dBi

Omni antenna** 8.15 dBi

Total Gain of Transmitter 24.7 dBi

Example Calculation - Transmitter SystemTo calculate the link loss of the transmitter system shown below, include the losses from each connector pair, the lightning arrestor, andthe cable.

* This is the rated gain of the SureCross DX80 radio.** Varies based on the antenna. Please refer to the technical specifications for the specific antenna used in the radio system.


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DX80 radio -

Connector pairs -1.5 dBi

Lightning arrestor -1 dBi

Cable (50 ft length) -1.95 dBi

Yagi antenna 8.15 dBi

Total Gain of Receiver 3.7 dBi

Example Calculation - Receiver SystemTo calculate the link loss of the transmitter system shown below, include the losses from each connector pair, the lightning arrestor, andthe cable.

Example Calculation - Free Space LossIn addition to losses from cabling, connectors, and lightning arrestors, radio signals also experience loss when traveling through the air.The equations for free space loss are:

FSL900MHz = 32 dB + 20 Log D (where D is in meters)

FSL900MHz

= 32 dB + 20 Log [5280 D/3.28] (where D is in miles)

FSL2.4GHz = 104.2 dB + 20 Log [3.28 D/5280] (where D is in meters)

FSL2.4GHz = 104.2 dB + 20 Log D (where D is in miles)

For a 900 MHz radio system transmitting three miles, the free space loss is:

FSL900MHz = 32 dB + 20 Log [5280 3/3.28]

FSL900MHz = 32 dB + 20 Log (4829.27)

FSL900MHz = 32 dB + 73.68 = 105.68 dB

Since this is a loss calculation, free space loss is always a negative number.

-0.5 dB

-0.5 dB

-0.5 dB

-1 dB

lightning arrestor

(N-type female to N-type male)cable

Yagi antenna

(6 dBd/8.15 dBi))

Losses:

-0.5 dB per connection

-1.0 dB per lightning arrestor

-3.9 dB per 100 ft of cable for LMR400 coax

Reverse polarity SMA connections

N-type female

N-type male

N-type male

N-type female

N-type femaleN-type male

NODE


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Transmitter System 24.7 dBi

Free Space Loss -105.68 dBiReceiver System 3.7 dBi

Total System -77.28 dBi

Example Calculation - Complete SystemThe total losses for the entire system is:

Compare the losses of the entire system to the sensitivity of the radio receiver to determine if the signal will be reliably received bysubtracting the receive sensitivity of the radio from the total system loss:

-77.28 dBi - (-104 dBm) = 26.72

If the result is greater than 10 dBi, the receiver should reliably receive the radio signal.


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Decibels - A logarithmic ratio between a specific value and a base value of the same unit of measure. With respect to radio power, dBmis a ratio of power relative to 1 milliWatt. According to the following equation, 1 mW corresponds to 0 dBm.

PmW = 10x/10 where x is the transmitted power in dBm, or

dBm = 10 log(PmW)

Another decibel rating, dBi, is defined as an antennas forward gain compared to an idealized isotropic antenna. Typically, dBm = dBi =dBd + 2.15 where dBi refers to an isotropic decibel, dBd is a dipole decibel, and dBm is relative to milliwatts.

EIRP (Effective Isotopic Radiated Power) - The effective power found in the main lobe of a transmitter antenna, relative to a 0 dBradiator. EIRP is usually equal to the antenna gain (in dBi) plus the power into that antenna (in dBm).

Free Space Loss (FSL) - The radio signal loss occurring as the signal radiates through free space. For the 900 MHz radio band,

FSL= 32dB + 20 Log D (where D is in meters).

FSL = 32dB + 20 Log (5280D/3.28) (where D is in miles)

For the 2.4 GHz band,

FSL = 104.2dB + 20 Log (3.28D/5280) (where D is in meters.)FSL = 104.2dB + 20 Log D (where D is in miles.)

Fresnel (FRA-nel) Zone Three-dimensional elliptical zones of radio signals betweenthe transmitter and receiver. Because the signal strength is strongest in the first zone anddecreases in each successive zone, obstacles within the first Fresnel Zone cause thegreatest amount of destructive interference.

Gain - Represents how well the antenna focuses the signal power. A 3dB gain antennadoubles the effective transmitting power while every 6 dB doubles the distance thesignal travels. Increasing the gain sacrifices the vertical height of the signal for horizontaldistance increases. The signal is squashed down to concentrate the signal strengthalong the horizontal plane.

Ground Plane - An electrically conductive plate that acts as a mirror for the antenna, effectively doubling the length of the antenna.When using a 1/4 wave antenna, the ground plane acts to double the antenna length to a 1/2 wave antenna.

Line of Sight - The clear path between radio antennas that is required for reliable communications.

Multipath Fade Obstructions in the radio path reflect or scatter the transmitted signal, causing multiple copies of a signal to reach thereceiver through different paths. The resulting phase difference between the direct signal and the indirect signal reduces the clarity ofthe transmission.

Signal-to-noise ratio (S/N or SNR) - A ratio of the signal to any background noise or noise generated by the medium. In radio terms,it a ratio of the transmitted radio signal to the noise generated by any electromagnetic equipment, in particular the radio receiver.The weaker the radio signal, the more of an effect noise has on radio performance. Like gain, the signal-to-noise ratio is measured indecibels.

The equations for calculating SNR are:

SNR = 20 log (Vs/Vn) where Vs is the signal voltage and Vn is the noise voltage;

SNR = 20 log (As/An) where As is the signal amplitude and An is the noise amplitude; or

SNR = 10 log (Ps/Pn) where Ps is the signal power and Pn is the noise power.

Since the noise or radio equipment can vary with environmental conditions, the signal-to-noise ratio indicates an average value.

System Operating Margin (also Fade Margin) - The difference between the received signal level (in dBm) and the receiver sensitivity(also in dBm) required for reliable reception. It is recommended that the receiver sensitivity be more than 10 dBm less than the receivedsignal level. For example, if the signal is about -65 dB after traveling through the air and the radio receiver is rated for -85 dB, theoperating margin is 20 dB - an excellent margin.

Glossary

1st Fresnel Zone

2nd Fresnel Zone

3rd Fresnel Zone

Tx Rx


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B E i i C 9714 T th A N Mi li MN USA 55441 Ph 763 544 3164 b i i E il @b i i

P/N 132113

WARRANTY: Banner Engineering Corp. warrants its products to be free from defects forone year. Banner Engineering Corp. will repair or replace, free of charge, any product of itsmanufacture found to be defective at the time it is returned to the factory during the warrantyperiod. This warranty does not cover damage or liability for the improper application of Bannerproducts. This warranty is in lieu of any other warranty either expressed or implied.

CAUTION . . .Make no modificationsto this product.

Any modifications to this product notexpressly approved by Banner Engineeringcould void the users authority to operatethe product. Contact the Factory for moreinformation.

All specifications published in this document are subject to change. Banner reserves the right tomodify the specifications of products, prior to their order, without notice.

132113 Antenna Basics

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