Chapter 1: Antenna & Introduction & Backgrounds Radio 1.2: Radio Propagation...

EELE 5333

Antenna & Radio

Propagation

Part I:

Antenna Basics

Winter 2020

Re-Prepared by

Dr. Mohammed Taha El Astal

Chapter 1:

Introduction & Backgrounds

1.2: Radio Propagation

Session 1

Chapter 1 – Introduction to Antenna

RADIO PROPAGATION

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1. Radio Spectrum

2. Radio Propagation


Radio Frequencies (1) 1.Radio Spectrum2.Radio Propagation

• A radio wave is an electromagnetic wave propagated byan antenna.

• Radio waves have different frequencies and by tuning aradio receiver to a specific frequency, you can pick up aspecific signal.

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Radio Frequencies (2)

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Frequency10 kHz to 30 kHz30 kHz to 300 kHz300 kHz to 3 MHz3 MHz to 30 MHz30 MHz to 328.6 MHz328.6 MHz to 2.9 GHz2.9 GHz to 30 GHz 30 GHz and above

BandVery Low Frequency (VLF) Low Frequency (LF) Medium Frequency (MF) High Frequency (HF)Very High Frequency (VHF) Ultra High Frequency (UHF) Super High Frequency (SHF) Extremely High Frequency (EHF)


MTIT and Frequency Bands

45

• In Palestine, the Palestinian Ministry of communication & IT (MTIT) is able to use which frequencies for which purposes.

• It issues licenses to stations for specificfrequencies.

• For example, AM radio stations must use frequencies in 535 KHz to 1.7 MHz band.

• FM radio stations transmit in band of frequencies from 88 MHz to 108 MHz.


Common Frequency Bands

46

• There are hundreds of frequency bands for different wireless technologies.

• Some examples:

– Cell phones: 824 to 849 MHz

– Global Positioning System: 1227 to 1575 MHz

– Garage Door Openers: Around 40 MHz

– Baby Monitors: 49 MHz

– MIR Space Station: 145 to 437 MHz

– Deep Space Communications: 2290 to 2300 MHz• Human voice also has its own frequency band.

– Voice’s frequency band is from 0 Hz to 4000 Hz


Duplexing (1)

47

• In some wireless systems, a radio unit will have capabilities to both transmitand receive (unlike a car radio but like a cell phone) at the same time. Theseradios are called full-duplex.

• In other systems, a radio unit can either transmit or receive at a given time.These radios care called half-duplex.


Duplexing (2)

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Examples?

Duplexing (3)

Walkie-talkie: Half-Duplex

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Cellular: Full-Duplex


Radio Channel

• There is another very important player in the wireless game: the physical environment over which radio waves travel.

• Radio waves can take many different paths to get from transmitter to receiver.

Transmitter

Receiver

1.Radio Spectrum2.Radio Propagation

50


Radio Channel

51

• Essentially, the radio waves interact with the physical environment along each of these paths.

• There are typically (unless you are in free-space) many paths from the transmitter to the receiver.

• Each path is called a multipath.


Multipaths

• The lengths of multipaths are different.

• As a result, sine waves along one path reach the receiver at different times than the same signal along a different path.

Transmitter

52

Receiver



Impact of Multipath (1)

Received radio wave along multipath 1

Received radio wave along multipath 2

The antenna combines (sums) these two multipaths.In the example above, the output of the antenna will be:

+ =

No Signal !!

53



• Whenever a radio wave bounces off or passes through a physical obstruction, the amplitude of the sine wave changes.

• Also amplitude of sine wave shrinks the further the radio wave travels, regardless of whether there areobstructions or not.

Originally transmitted radio wave

Reflection

A

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-A

Receivedradio wave, < 1

A

A



A

-A

Radio Channel: Impact of Physical

Environment

Transmitted radio wave

Overall combinedreceived signal atreceive antenna

• When all the radio waves on the multiple paths reach the receiver’s antenna, they combine together.

• Some multipaths cancel each other out, some add up together constructively, some partially cancel each other, etc.

Signal fades in and out

and is distorted

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Fading (1)

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• Fading, which is both signal attenuation and distortion, is a major challenge in wireless communications.

• We have all experienced it, e.g., fading of radio station in a car radio.

• Fading varies in frequency: assuming physical conditions are fixed, if a signal transmitted at one frequency fades, it may not if transmitted at a different frequency.



Problem with Distortion

57

• Distortion not only impacts the strength of the received signal but also changes the “shape” of the received signal.

• In this digital communications, this can be especially detrimental because bits can be inverted at the receiver due to multipath. Example is shown in next slide.


Fading (2)

1 0 0

Transmitted Signal

Overall Received Signal

Signal along Multipath 2

This type of distortion occurs anytime there is long time spread in the multipaths.

1 1 0

Signal along Multipath 1

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Fading (3)

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• Time spread of multipaths = delay due to echoes.

• These “echoes” are particularly problematic in urban areas, due to reflections from buildings.

• Also problematic in hilly, mountainous areas

• Designers of radio systems have spent a lot of time and effort trying to overcome this fading challenge.


Summary

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1.Radio Spectrum, MTIT,…2.Duplexing3.Fading effects


Next Class:

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• One Solution: Multiple Antennas

• Another Solution: Adaptive Antenna Array

• PROPAGATION TECHNIQUES

• Radio Propagation Effects

Dr. Mohammed Taha El [email protected]@gmail.com

9/2020

EELE 5333

Antenna & Radio

Propagation

Part I:

Antenna Basics

Winter 2020

Re-Prepared by

Dr. Mohammed Taha El Astal

Chapter 1:

Introduction & Backgrounds

1.2: Radio Propagation

Session 2


Fading (3)

• Time spread of multipaths = delay due to echoes.

• These “echoes” are particularly problematic in urban areas, due to reflections from buildings.

• Also problematic in hilly, mountainous areas, like Susquehanna County.

• Designers of radio systems have spent a lot of time and effort trying to overcome this fading challenge.


One Solution: Multiple Antennas

• One way to overcome fading problem is to design receivers with multiple, say 2, antennas.

• Both antennas can receive the desired radio wave.

Transmitter

Receiver


Multiple Antennas (2)

• If receive antennas are adequately separated, then paths followed by radio waves to the first antenna are different from paths followed by radio waves to the second antenna.

• Result: fading of received signal on firstantenna is different from fading of receivedsignal on second antenna. Chances are if oneantenna experiences a deep fade, the otherdoes not.

• Receiver can adaptively choose the “stronger” antenna to determine the received radio wave at any given time.


Multiple Antennas (3)

Cellular base station tower (antenna tower that cell phones “talk” to) use multiple antenna to improve the quality of voice signal received from cell phone users.

Several combining techniques instead of just select one, SC/ EGC/MRC


Another Solution: Adaptive Antenna Array

• Of all the multipath, if there is a line-of-sight (LOS) path between the transmitter and receiver, it is the strongest.

• If we can design antennas receive patter, we would like to make it in the direction of the strongestmultipath.

• This is what adaptive antenna arraydo.


Adaptive Antenna Array (2)• Adaptive antenna array is a group of

receive antennas that work together to form a desirable radiation pattern.

• For example, if the LOS path is in a particular direction, the antennas work together to pick out as many radio waves in that direction as possible.

• In doing so, the antennas ignore radio waves in non-significant directions. These waves do not contribute to the overall fading.


Cellular Tower Example

Assume that a cellular base station tower is receiving signal from four cell phone users. The tower can use its antennas to form the following radiation power (bird’s eye view).

Cellular Base Station

User 1

User 2

User 3

User 4

No signals received from this direction




TransmissionMedium

PROPAGATION TECHNIQUES

A signal can be propagated in 3 ways:

1. Ground-Wave (surface wave) Propagation

2. Space wave (Line-of-Sight/Ground reflected) Propagation

Frequency > VHF

2. Sky-Wave Propagation

Frequency HF/MF


Types of Waves


Radio Frequency Bands

Classification Band Initials Frequency Range Characteristics

Extremely low ELF < 300 Hz

Ground waveInfra low ILF 300 Hz - 3 kHz

Very low VLF 3 kHz - 30 kHz

Low LF 30 kHz - 300 kHz

Medium MF 300 kHz - 3 MHz Ground/Sky wave

High HF 3 MHz - 30 MHz Sky wave

Very high VHF 30 MHz - 300 MHz

Space wave

Ultra high UHF 300 MHz - 3 GHz

Super high SHF 3 GHz - 30 GHz

Extremely high EHF 30 GHz - 300 GHz

Tremendously high THF 300 GHz - 3000 GHz


Radio Propagation Effects


Summary

1. Basic Antenna Operation

– core component in radio system

– Works in both transmitter /receiver

– Design influenced heavily on operational frequency

2. Radio Propagation

– physical environment over which radio waves travel

– Challenges – multipath, fading, distortion


Next Class:

• Antenna Parameters:

– The vocabulary of antenna: Radiation pattern, Directivity, Efficiency, Gain and more…

Dr. Mohammed Taha El [email protected]@gmail.com

10/2020

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Chapter 1: Antenna & Introduction & Backgrounds Radio 1.2: Radio Propagation...

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