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.
Chapter 1 – Introduction to Antenna
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?
Chapter 1 – Introduction to Antenna
Radio Concept1. What?
2. Where?
3. How?
4. Why?
Simple Transmitter (1) Simple Transmitter (2) Simple Transmitter (3)
Chapter 1 – Introduction to Antenna
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.
Chapter 1 – Introduction to Antenna
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)
Chapter 1 – Introduction to Antenna
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:
Chapter 1 – Introduction to Antenna
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
Chapter 1 – Introduction to Antenna
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
Chapter 1 – Introduction to Antenna
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.
Chapter 1 – Introduction to Antenna
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
Chapter 1 – Introduction to Antenna
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
Chapter 1 – Introduction to Antenna
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
Chapter 1 – Introduction to Antenna
Decibel (dB)
Chapter 1 – Introduction to Antenna
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
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
Chapter 1 – Introduction to Antenna
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
Chapter 1 – Introduction to Antenna
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?
Chapter 1 – Introduction to Antenna
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.
Chapter 1 – Introduction to Antenna
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.
Chapter 1 – Introduction to Antenna
Types of Antennas (1)• Wire Antennas– dipoles, monopoles, loops, helix, …
– most common
– personal, automobiles, buildings, ships, aircraft, spacecraft …
Chapter 1 – Introduction to Antenna
Types of Antennas (1)
• Aperture Antennas
– horns, waveguide opening …
– can be flush-mounted
– aircraft, spacecraft …
Chapter 1 – Introduction to Antenna
Types of Antennas (1)
• Microstrip Antennas
– metallic patch above a ground plane, e.g. circular, rectangular …
– low profile
– personal, aircraft, spacecraft, satellites, missiles, cars, mobile phones …
Chapter 1 – Introduction to Antenna
Types of Antennas (2)
• Array Antennas
– Yagi-Uda, aperture array, microstrip patch array, slotted-waveguide array …
– controllable radiation pattern
Chapter 1 – Introduction to Antenna
Types of Antennas (2)
• Reflector Antennas
– parabolic, corner reflector …
– high gain
Chapter 1 – Introduction to Antenna
Types of Antennas (2)
• Lens Antennas
– convex-plane, convex-convex, convex-concave, concave-plane …
– good for very high frequency applications
– size and weight disadvantages
Chapter 1 – Introduction to Antenna
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
Chapter 1 – Introduction to Antenna
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
Chapter 1 – Introduction to Antenna
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.
Chapter 1 – Introduction to Antenna
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?
Chapter 1 – Introduction to Antenna
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.
Chapter 1 – Introduction to 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
Chapter 1 – Introduction to Antenna
Summary
1. Basic Antenna Operation
– core component in radio system
– Works in both transmitter /receiver
– Design influenced heavily on operational frequency
Chapter 1 – Introduction to Antenna
Next Class:
P2: Radio Propagation
– physical environment over which radio waves travel
– Challenges – multipath, fading, distortion