Radiation Pattern

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Example of a Real Antenna

stallings05wireless: 5.1

Conductor

Conductor Gap

Image: http://www.elektronik-

kompendium.de/sites/kom/0810171.htm

Image: http://de.wikipedia.org/

wiki/Dipolantenne

Resonant Circuit

/2

Electric Field E Magnetic Field H

Half-Wave Dipole (Hertz Antenna)

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Radiation Pattern

Image: http://en.wikipedia.org/

wiki/Radiation_pattern

Example: radiation pattern of a half-wave dipole

x y

z y

x z

• a common way to characterize the performance of an antenna

• due to reciprocity: radiation pattern characterizes both transmission and reception performance

• when an antenna is used for reception, the

radiation pattern becomes a reception pattern

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The size of the pattern does not matter

What is important is the relative distance from the antenna position in each direction. The relative distance characterizes the relative power in that direction compared to other

directions.

Examples

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Beam Width

The angle within which the power radiated by the antenna is at least half of what it is in the most preferred direction

Beispiel

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Antenna Gain

Power output in a particular direction compared to the power output produced in any direction by a perfect isotropic antenna.

(i.e. total area of both radiation patterns of the isotropic antenna and the considered one are the same)

Example: what is the antenna gain into the strongest direction?

(Note: an increase of power in one direction means a lowering of power

into another one; antenna gain does not mean amplification of the total

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Effective Area (1)

Consider the amount PFD [watt/m²] (power flux density) of power passing through a unit area of one square meter.

Consider an antenna oriented with the axis of maximum sensitivity toward the source. Let the antenna deliver P_o watts to the receiver.

The effective area A_e is defines as:

Basically it expresses the size of the area oriented perpendicular to the direction of an incoming electromagnetic wave which would intercept P_owatt (i.e. the power intercepted by the considered antenna).

Transmit antenna

Receive antenna

Image: lecture slides

„Mobilkommunikation, Prof. Dr. Holger Karl

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Effective Area (2)

Without further details: the effective area is of course related to the physical size and type of the antenna. (how depends on the antenna type)

Antenna gain G and effective area A_e are related. Let  be the wave length. We have:

Note: we considered an antenna oriented with the axis of maximum sensitivity toward the source. The concept can of course be generalized to any antenna orientation.

Example of antenna gains and effective areas for different antenna types

Type of Antenna Effective Area A_e[m²] Antenna Gain G

into the strongest direction

Isotropic ² / (4 π) 1

Half‐wave dipole 1.64 ² / (4 π) 1.64

Parabolic with face area A (see next) 0.56 A 7 A / ²

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What is the beam width?

What is the antenna gain in an arbitrary direction?

Quiz: radiation pattern of an isotropic antenna?

x y

z y

x

z

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Antenna examples:

quarter wave antenna (Marconi antenna)

Image source: http://en.wikibooks.org/wiki/

Communication_Systems/Antennas

/4

Surface acts as a „mirror“ for the lambda/4 radiator (example: radio antenna in the roof of a car)

Image source: Jochen Schiller,

„Mobilkommunikation“, 2te überarbeitete Auflage, 2003

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Antenna examples:

inverted‐F antenna (IFA) of a TmoteSky node

Where is the antenna?

Such an antenna is also called a PCB antenna (printed circuit board antenna)

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Antenna examples:

radiation pattern from the TmoteSky data sheet

Horizontal mounting Vertical mounting

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Antenna examples: parabolic reflective antenna

x y

Focus

same length

Directrix

Parabola construction Reflective property

x

y

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Antenna examples:

radiation pattern of a parabolic reflective antenna

x y

z y

x

z

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Antenna beamwidths for various parabolic reflective antenna diameters at frequency f=12GHz

Antenna diameter (m) Beam width (in degree)

0,5 3,5

0,75 2,33

1,0 1,75

1,5 1,166

2,0 0,875

2,5 0,7

5,0 0,35

Parabolic reflective antennas always have a beam with >0. In practice the focus is not one single idealized point. Note: the larger the antenna diameter the more tightly directional is the beam.

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Physical size of an antenna

For the parabolic reflecting antenna the antenna size is the diameter parabolic reflector

For the considered lambda/x antenna the antenna size is proportional to the utilized wave length

The size of the example antenna of the TmoteSky node (more precisely the height of th “ ground plane” ) is approximately 3,125cm and is ¼ of the wave length

(lambda/4 antenna).

Which frequency band is probably used?

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More about antenna types

• This was a small example selection of antenna types: a list of many more elementary antenna types can be found here:

http://www.antenna‐theory.com/antennas/main.php

• Moreover elementary antenna types can be used to build

more complex ones: see next...

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Antennen: gerichtet und mit Sektoren

Seitenansicht (xy-Ebene) x y

Seitenansicht (yz-Ebene) z y

von oben (xz-Ebene) x z

von oben, 3 Sektoren x z

von oben, 6 Sektoren x z

Häufig eingesetzte Antennenarten für direkte

Mikrowellenverbindungen und Basisstationen für Mobilfunknetze (z.B. Ausleuchtung von Tälern und Straßenschluchten)

gerichtete Antenne

Sektoren-

antenne

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Antennen: Diversität



Gruppierung von 2 oder mehr Antennen



Antennenfelder mit mehreren Elementen



Antennendiversität



Umschaltung/Auswahl

 Empfänger wählt die Antenne mit dem besten Empfang



Kombination

 Kombination der Antennen für einen besseren Empfang

 Phasenanpassung um Auslöschung zu vermeiden

+

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/2

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Grundfläche

/2

+

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MIMO

Multiple-Input Multiple-Output

 Use of several antennas at receiver and transmitter

 Increased data rates and transmission range without additional transmit power or bandwidth via higher spectral efficiency, higher link robustness, reduced fading

Examples

 IEEE 802.11n, LTE, HSPA+, …

Functions

 “Beamforming”: emit the same signal from all antennas to maximize signal power at receiver antenna (and beamforming at the receiver side also possible; reduces interference)

 Spatial multiplexing: split high-rate signal into multiple lower rate streams and transmit over different antennas

sender

t₁

t₂ t₃

Time of flight t₂=t₁+d₂

1 2

3

Sending time 1: t₀

2: t -d

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Übersicht

Elektromagnetische Wellen

Frequenzen und Regulierungen Antennen

Signale

Signalausbreitung Multiplex

Modulation

Bandspreizverfahren

Codierung

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Signale I



Physikalische Darstellung von Daten



Signalparameter: Kenngrößen, deren Wert oder Werteverlauf die Daten repräsentieren



Einteilung in Klassen nach Eigenschaften:



zeitkontinuierlich oder zeitdiskret



wertkontinuierlich oder wertdiskret



Analogsignal = zeit- und wertkontinuierlich



Digitalsignal = zeit- und wertdiskret

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Problem: Wireless = Analog

0110 1001 1000 1010

Transmitter Receiver

0110 1001 1000 1010

Definition: Transmitter + Receiver = Transceiver

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Bandpass Transmission Principle

0110 1001 1000 1010

Transmitter Receiver

0110 1001 1000 1010 Carrier wave with

carrier frequency f

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Terminology

1011

Bit(s) Symbol

Modulation

Demodulation

Symbol rate:

Number of Symbols per second

Data rate:

Number of Bits per seconds

N-ary modulation scheme: number of different symbols!

i.e., this can convey log(N) Bits per symbol

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Erinnerung: Fourier-Repräsentation periodischer Signale

) 2

cos(

) 2

2 sin(

) 1 (

1 1

nft b

nft a

c t

g

n n n

n

  



^











1

0

1

0

t t

ideales periodisches Signal reale Komposition

(basierend auf

Harmonischen)

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

Verschiedene Darstellungen eines Signals:



Amplitudenspektrum (Amplitude über Zeit)



Frequenzspektrum (Amplitude oder Phase über Frequenz)



Phasenzustandsdiagramm (Amplitude M und Phasenwinkel φ werden in Polarkoordinaten aufgetragen)



Zusammengesetzte Signale mittels Fourier-Transformation in Frequenzkomponenten aufteilbar



Digitalsignale besitzen Rechteckflanken



im Frequenzspektrum unendliche Bandbreite



zur Übertragung Modulation auf analoge Trägersignale

Signale II

f [Hz]

A [V]



I = M cos φ (In-phase) Q = M sin φ (Quadrature)

 A [V]

t[s]

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Übersicht

Elektromagnetische Wellen

Frequenzen und Regulierungen Antennen

Signale

Signalausbreitung



Motivation



Statische Knoten



Mobile Knoten



Zusammenfassung Multiplex

Modulation

Bandspreizverfahren

Codierung

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Wir wollen folgende hier dargestellte Effekte verstehen; was geht hier schief?

Bildquelle: Theodore S. Rappaport, Wireless Communications, 2nd ed., Prentice Hall, 2002

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Randbemerkung: Was ist dB?

Logarithmische Darstellung von im Verhältnis stehenden gleichartigen (d.h. gleiche Einheitengröße) Leistungs- bzw. Energiegrößen

Am Beispiel: Für P

₁

und P

₂

ist das Verhältnis P

₂

/ P

₁

definiert als:

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Note: What is dBm?

Logarithmic expression of power in mW Conversion



P mW  x dBm



x dBm  P mW

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Examples (from wikipedia)

dBm level Power Notes

80 dBm 100 kW Typical transmission power of a FM radio station

60 dBm 1 kW = 1000 W Typical RF power inside a microwave oven

36 dBm 4 W Typical maximum output power for a Citizens' band radio station (27 MHz) in many countries 30 dBm 1 W = 1000 mW Typical RF leakage from a microwave oven - Maximum output power for DCS 1800 MHz mobile

phone

27 dBm 500 mW Typical cellular phone transmission power

21 dBm 125 mW Maximum output from a UMTS/3G mobile phone (Power class 4 mobiles) 20 dBm 100 mW Bluetooth Class 1 radio, 100 m range (maximum output power from unlicensed FM transmitter)

4 dBm 2.5 mW Bluetooth Class 2 radio, 10 m range

0 dBm 1.0 mW =

1000 µW Bluetooth standard (Class 3) radio, 1 m range

−70 dBm 100 pW Typical range (−60 to −80 dBm) of Wireless signal over a network

−111 dBm 0.008 pW Thermal noise floor for commercial GPS signal bandwidth (2 MHz)

−127.5 dB 0.000178 pW Typical received signal power from a GPS satellite