chapter 1: antenna & introduction & backgrounds radio 1.1...

EELE 5333

Antenna & Radio

Propagation

Part I:

Antenna Basics

Winter 2020

Re-Prepared by

Dr. Mohammed Taha El Astal

Chapter 1:

Introduction & Backgrounds

1.1: Basic Antenna Operation

Session 1

Chapter 1 – Introduction to Antenna

Basic Antenna Operation1. What?

2. Where?

3. How?

4. Why?

• Our ‘operational ’life today depends on wireless network

– Cellular Telephony

– Global Positioning Systems

– WiFi

• Wireless technologies use radio waves tocommunicate.


Radio Waves

• Radio waves carry information invisibly through the air over millions of miles.

• Radios can transmit and/or receive radio waves.

1. What?

2. Where?

3. How?

4. Why?


Radio Concept1. What?

2. Where?

3. How?

4. Why?

Simple Transmitter (1) Simple Transmitter (2) Simple Transmitter (3)


Simple Transmitter (3)

• Changing the magnetic field in one wire causes change in the electric field in the second wire.

• Specifically,– Battery creates electron flow in one wire

– Moving electrons create magnetic field around one wire

– Magnetic field stretches out to second wire

– Electrons flow in second wire whenever magnetic field in first wire changes.

• Electrons flow in second wire only when you connect/disconnect battery.


Simple Transmitters (4)

• When we change current in first wire in time, a current is induced in second wire.

• To create any radio transmitter, create a rapidly changing electric current in a wire.

• This can be done by connecting/disconnecting a battery. When connected, voltage in wire is 9V. When disconnected voltage in wire is 0V. Result: square wave signal.

9V

0V

Time (s)


Simple Transmitters (5)

• A better alternative to square wave is a continuously varying electric current in a wire.

• Simplest and smoothest continuously varying wave is a sine wave:


Cont.

• By sending sine wave electric current to antenna, you can transmit sine wave into space.

• All radios today, however, transmit continuous sine waves to transmit information (audio, video, data).

Why sine waves?

• To allow many different people/devices to use radio waves at the same time.

Frequency Spectrum

18

100MH

z

Waveguide Coaxial Cable Twisted Pair Cable

Infrared

Visib

le

Ultrav

iolet

Optical Fiber

Extra

Hig

hF

requ

ency

E

HF

Su

per

Hig

h

Freq

uen

cy

SH

F

Ultra

Hig

hF

requ

ency

UH

F

Very

Hig

hF

requ

ency

VH

F

Hig

h

Freq

uen

cy

HF

Med

ium

F

requ

ency

M

F

Lo

w

Freq

uen

cy

LFVery

Lo

w

Freq

uen

cy

VL

F

Au

dio

Line-of-sight radio

Skywave radio

Groundwave radio

Wavelength

Frequency designations

Transmission media

Propagation modes

Representative applications

Frequency

Laser beam

100km 10km 1km 100m 10m 1m 10cm 1cm 10-6m

Teleph

on

eT

elegrap

h

UH

FT

VM

ob

il and

Aero

nau

tical

VH

F T

V an

dF

M

Mo

bil

radio

CB

radio

Am

ateur

radio

AM

bro

adcastin

g

Aero

nau

ticalS

ub

marin

e cable

Nav

igatio

n

Tran

socean

icrad

io

Bro

adb

and

PC

SW

irelessco

mm

un

ication

C

ellular,P

ager

Satellite-satellite

Micro

wav

erelay

E

arth-satellite

Rad

ar

Wid

eban

dd

ata

1kH

z

10kH

z

100kH

z

1MH

z

10MH

z

1GH

z

10GH

z

1G0H

z

101

4Hz

101

5Hz


RF Band Names

Band Name Abbr. Frequency Wavelength Examples of Usage

Extremely Low Frequency ELF 3-30 Hz 10-100 Mm

Super Low Frequency SLF 30-300 Hz 1-10 Mm power lines

Ultra Low Frequency ULF 0.3-3 kHz 0.1-1 Mm

Very Low Frequency VLF 3-30 kHz 10-100 km submarines

Low Frequency LF 30-300 kHz 1-10 km beacons

Medium Frequency MF 0.3-3 MHz 0.1-1 km AM broadcast

High Frequency HF 3-30 MHz 10-100 m short-wave radio

Very High Frequency VHF 30-300 MHz 1-10 m FM and TV broadcast

Ultra High Frequency UHF 0.3-3 GHz 0.1-1 m TV, WiFi, mobile phones, GPS

Super High Frequency SHF 3-30 GHz 10-100 mm radar, satellites, WLAN data

Extremely High Frequency EHF 30-300 GHz 1-10 mm radar, automotive, data


Frequency – Wavelength Relationship

• The wavelength of an electromagnetic wave is related to its

frequency f by:

• Conveniently in practice, we can quickly estimate the wavelength of

a frequency given in MHz or GHz by:

f

c where c = 3x108 m/s

(speed of light in vacuum)

300

( m ) fMHz

300

( mm )fGHz

e.g., of 100 MHz is 3m.

e.g., of 10 GHz is 30mm.

One cycle of a sine wave is : Sine wavecan be written as sin(2t/T)

T seconds1 Hz = 1 cycle/second.


Decibel (dB)

• Used to measure the ratio between 2 values – value to be measured relative to a reference value

• In the electronic communication field, decibel is normally used to define the power ratios between 2 signals

– To express relative gain /lose of the electronic device/circuit

– Describing relationship between signal and noise

• In the common usage, it also used to express the ratios of voltage and current

• If 2 powers are expressed in the same units (e.g. watt, miliwatt), their ratio is a dimensionless quantity that can be expressed in decibel form as follow

(1) P2

P1 dB 10log10 P1 : power level 1 (watts)

P2 : power level 2 (watts)

• the dB value is for the power of P1 with respect to the reference power P2

• the dB value shows the difference in dB between power P1 andP2


Decibel (dB)

• In the case to measure the power gain or loss of any electronic circuit or device, equation (1) can be written as follow

(2)

where Ap(dB) : power gain (unit in dB) of Pout with respect to Pin

Pout

Pin

: output power level (watts)

: input power level (watts)

Pout/Pin : absolute power gain (unitless)

– Positive (+) dB value indicates the output power is greater than the input power, which indicates power gain or amplification

– Negative (-) dB value indicates the output power is less that the input power which indicates power loss or attenuation

– If Pout = Pin, the absolute power gain is 1, which means dB power gain is 0 (referred as unity power gain)

Pin

Pout Ap(dB) 10log10


Decibel (dB)

• Expressing power gain in term of voltage ratio

From

(3)

Substituting (3) into (2),

i.e. (3-1)

Voltage Gain

(3-2)

Vout 2

dB 10log102Vin

Vin

Vout

Av(dB) 20log10

PV 2


Decibel (dB)


Example

• To calculate the ratio of 1 kW (one kilowatt, or 1000 watts) to 1 W in decibels, use the formula

• To calculate the ratio of 1 mW (one milliwatt) to 10 W in decibels, use the formula

• To find the power ratio corresponding to a 3 dB change in level, use the formula

• End of session 1/ ch 1- sec1.1

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

1.1: Basic Antenna Operation

session2


Transmitter/Receiver Description.

Information (voice message)

Radio Transmitter

Combine Antenna

Sine

Wave

Radio Waves

Transmitter generates its own sine wave using oscillators.

1. What?

Where?

3. How?

4. Why?

Separate

Sine Wave

Radio Transmitter

Antenna

Information (voice message)

Antenna as an Interface/Transducer

RF Generator

(including

Transmission

Line)

EM wave

radiating

into space

Antenna

Antennas are conducting or dielectric structures that allow efficient launching or radiating of electromagnetic waves into space. (Theoretically, any structure can radiate EM waves but not all structures can do it efficiently.)

An antenna can be viewed as a transducer between a transmission line (or directly from an electrical or electronic circuit) and the surrounding medium. It can be used for either transmitting or receiving.

wave front of

EM wave


Antenna (1)

• Every radio requires an antenna.

• Antennas come in all shapes and sizes. Shapes and sizes depend on the frequency the antenna is trying to receive.

• Ranges from long stiff wire (as in car radios) to large satellite dishes (as used by NASA).

• For satellites that are millions of miles away NASA uses antenna dishes that 200 feet wide.

1. What?

2. Where?

3. How?

4. Why?


Antenna (2)

• Often radio stations use extremely tall

antenna towers to transmit their signals.

• Antenna at radio transmitter: launch

radio signals into space.

• Antenna at radio receiver: pick up as

much of the transmitter’s power as

possible and feed it to the tuner.


Antenna (3)

• Size of optimum radio antenna is related to frequency of the signal antenna is trying to transmit and/or receive.

• Reason for this: speed of light and the distance electrons can travel as a result.

• Speed of light is 300,000 meters/sec.


Types of Antennas (1)• Wire Antennas– dipoles, monopoles, loops, helix, …

– most common

– personal, automobiles, buildings, ships, aircraft, spacecraft …


Types of Antennas (1)

• Aperture Antennas

– horns, waveguide opening …

– can be flush-mounted

– aircraft, spacecraft …



• Microstrip Antennas

– metallic patch above a ground plane, e.g. circular, rectangular …

– low profile

– personal, aircraft, spacecraft, satellites, missiles, cars, mobile phones …



• Array Antennas

– Yagi-Uda, aperture array, microstrip patch array, slotted-waveguide array …

– controllable radiation pattern



• Reflector Antennas

– parabolic, corner reflector …

– high gain



• Lens Antennas

– convex-plane, convex-convex, convex-concave, concave-plane …

– good for very high frequency applications

– size and weight disadvantages


Antenna Size (1)

• Say you are building an antenna tower for radio station 680K AM.

• It is transmitting sine wave with frequency of 680,000 Hz.

• In one cycle of sine wave, transmitter is going to move electrons in the antenna in one direction, switch and pull them back, switch push them out, and switch and pull them back.

• That is electrons change direction four times during one cycle of the sine wave.

time


Antenna Size (2)

• When operating at 680,000 Hz, each cycle completes in 1/680,000 = 0.00000147 (1.47 µsec) seconds.

• One quarter of the cycle is 0.0000003675 (0.3675 µsec) seconds.

• At the speed of light, electrons can travel 110 meter in 0.0000003675 seconds.

• Cell phones operate using 900,000,000 Hz; this means that it needs antennas that are about 1/12 meter (8.3 cm) high.

It needs nearly antenna with height of 110 meters


Antenna Size (3)

• Question: why aren’t car radio antennas 110 feet high?

• It would be impractical for one.

• If you made car radio antenna higher, reception would be better.

• AM radio stations transmit at high powers to compensate for the suboptimal receive antenna heights.


Some Questions

• Why do radio waves transmit away from antenna into space at speed of light?

• How can radio waves transmit millions of km?

• Doesn’t antenna only create magnetic field in its vicinity?

• How can the magnetic field variation be registered millions of km away?


Answer

• When current enters antenna, it creates a magnetic field around the antenna. This magnetic field creates an electric field (voltage and current) in another wire placed close to the antenna.

• In space, magnetic field created by antenna induces electric field in space.

• This electric field induces another magnetic field in space, which induces another electric field, …

• These electric and magnetic fields (electromagnetic fields) induce each other in space at the speed of light in a direction away from the antenna.


New Challenges in Antenna Design

• Phase-arrays integrated with monolithic MIC

• Use of new materials (e.g., ceramic dielectric, metamaterials, artificial magnetic conductors, soft/hard surfaces)

• Use of supercomputing/parallel computing to model complex EM wave interactions in both frequency and time domains

• Smart antennas, multifunction, reconfigurable antennas and antenna systems

• New applications including wireless communications, direct broadcast satellite system, GPS, global weather, earth resource systems, etc.

• Pushing into higher frequencies, including mm waves


Summary

1. Basic Antenna Operation

– core component in radio system

– Works in both transmitter /receiver

– Design influenced heavily on operational frequency


Next Class:

P2: Radio Propagation

– physical environment over which radio waves travel

– Challenges – multipath, fading, distortion

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

9/2020

chapter 1: antenna & introduction & backgrounds radio 1.1...

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