rfm_pdd day 3
TRANSCRIPT
© Okey Ugweje, PhD Page 1
RF/Microwave Systems: Planning, Design &
Deployment
Day 3
Antennas & Transmission LinesAntennas & Transmission Lines
© Okey Ugweje, PhD Page 2
Antennas Antenna Basics Radiation Pattern Antenna types, composition and operational
principles Antenna gains, patterns, and selection principles Types of Antennas Line-of-Sight Microwave
Antennas Antenna Basics Radiation Pattern Antenna types, composition and operational
principles Antenna gains, patterns, and selection principles Types of Antennas Line-of-Sight Microwave
Day 3
RF/Microwave Systems : PDDProgram Schedule
RF/Microwave Systems : PDDProgram Schedule
© Okey Ugweje, PhD Page 3
RF/Microwave SystemsRF/Microwave Systems
AntennasAntennas
© Okey Ugweje, PhD Page 4
RF/Microwave SystemsRF/Microwave Systems
Antenna BasicsAntenna Basics
Antenna Concepts and DefinitionsElectromagnetic Fields and CharacterizationRadiation PatternGain Antenna types, composition and
operational principlesAntenna gains, patterns, and selection
principlesAntenna system testing
Antenna Concepts and DefinitionsElectromagnetic Fields and CharacterizationRadiation PatternGain Antenna types, composition and
operational principlesAntenna gains, patterns, and selection
principlesAntenna system testing
© Okey Ugweje, PhD Page 5
RF/Microwave SystemsRF/Microwave Systems
Antenna Concepts and Definitions
Antenna Concepts and Definitions
© Okey Ugweje, PhD Page 6
Concepts and DefinitionsConcepts and DefinitionsWhat is an antenna? Antenna is a passive device that transmit & receive EM wave Antennas do not require external power to operate
What is an antenna? Antenna is a passive device that transmit & receive EM wave Antennas do not require external power to operate
© Okey Ugweje, PhD Page 7
Concepts and DefinitionsConcepts and Definitions The purpose of any antenna is to: Provide a transition between a transmission line and a
free-space radiation To do this, an antenna should
1. have good impedance match (low reflection coefficient) with the transmission line
2. have low ohmic losses (high transmission coefficient)3. direct energy with desired antenna gain in the desired
angular sectors Provide angular selectivity (directivity) for
transmission or reception of plane waves4. minimize energy radiated into undesired sectors
The purpose of any antenna is to: Provide a transition between a transmission line and a
free-space radiation To do this, an antenna should
1. have good impedance match (low reflection coefficient) with the transmission line
2. have low ohmic losses (high transmission coefficient)3. direct energy with desired antenna gain in the desired
angular sectors Provide angular selectivity (directivity) for
transmission or reception of plane waves4. minimize energy radiated into undesired sectors
© Okey Ugweje, PhD Page 8
Antennas do not amplify RF energy It can only radiate (at max) what is put into it
If I00% efficient, an antenna will not radiate, more, total power than is delivered to it
Antennas function as directional amplifiers over some specified frequency bandwidth
Antennas do not amplify RF energy It can only radiate (at max) what is put into it
If I00% efficient, an antenna will not radiate, more, total power than is delivered to it
Antennas function as directional amplifiers over some specified frequency bandwidth
© Okey Ugweje, PhD Page 9
EM Fields and CharacterizationEM Fields and CharacterizationWhat is an Electric Field?An electric field applies a force on a charge at a distance
where q is the charge in Amps, or coulombs, CThe charge on one electron is 1.6x10-19 C and is the
electric field strength in Volts/m
When a charge, q, is placed in an electric field, a force F will be exerted on it
What is a Magnetic Field?A magnetic field applies a force on a moving charge
What is an Electric Field?An electric field applies a force on a charge at a distance
where q is the charge in Amps, or coulombs, CThe charge on one electron is 1.6x10-19 C and is the
electric field strength in Volts/m
When a charge, q, is placed in an electric field, a force F will be exerted on it
What is a Magnetic Field?A magnetic field applies a force on a moving charge
F qE
E
/E F q
F qv B ������������������������������������������
© Okey Ugweje, PhD Page 10
where is the velocity of q in meters/s, and is the magnetic
flux density in weber/meter2 (N/Cs/meters)
Therefore, the total force on a moving charge is
Properties of EM waves in Free SpaceElectric field and magnetic fields are orthogonalThe direction of propagation of the EM wave is orthogonal
to both the electric and magnetic fields
where is the velocity of q in meters/s, and is the magnetic flux density in weber/meter2 (N/Cs/meters)
Therefore, the total force on a moving charge is
Properties of EM waves in Free SpaceElectric field and magnetic fields are orthogonalThe direction of propagation of the EM wave is orthogonal
to both the electric and magnetic fields
F qv B ������������������������������������������
v
B��������������
F q E v B �������������� ������������������������������������������
© Okey Ugweje, PhD Page 11
Plane Wave Propagation E field in orientated along the x axisB field in orientated along the y axisE & B are orthogonal to each otherBoth E & B oscillate at the same
frequency as they propagateEM wave is propagating in the z directionK, the direction of propagation is
orthogonal to both E and BThe EM wave is horizontal (y) polarized
K is the direction of propagationThe polarization of the EM wave is defined by the orientation of
the electric field
© Okey Ugweje, PhD Page 12
Frequency, Time and Space
Frequency (f), that an EM wave oscillates
is expressed in Hertz (cycles/sec).
Period (T)time it takes to compete one
cycle of oscillation, T = 1/f sec.
EM waves propagate in free space at the speed of light, c = 3 x 108 m/s
Wavelength () the distance the field travels
during one cycle
Distance c
f
© Okey Ugweje, PhD Page 13
Phase Phase expresses the directional relationship between two or
more time or spatially varying vectorsmeasure of the relative position in time within a single period
of the signalSpectrumrange of frequencies that a signal contains
Absolute bandwidthwidth of the spectrum of a signal
Effective bandwidth (or just bandwidth)narrow band of frequencies that most of the signal’s energy
is contained in
© Okey Ugweje, PhD Page 14
Planewave PropagationPlanewave PropagationThe time variation of an electric
field operating at frequency, f can be expressed as Re{ej2ft}, which means that it oscillates (i.e., rotate in phase by 2) every 1/f seconds
c = λ f, therefore the time to travel a distance λ, is t = λ /c or 1/f
Therefore, the electric field changes phase by 2 for each wavelength of propagation
The time variation of an electric field operating at frequency, f can be expressed as Re{ej2ft}, which means that it oscillates (i.e., rotate in phase by 2) every 1/f seconds
c = λ f, therefore the time to travel a distance λ, is t = λ /c or 1/f
Therefore, the electric field changes phase by 2 for each wavelength of propagation
All the energy in a planewaveis in phase on the plane perpendicular to the direction of propagation
© Okey Ugweje, PhD Page 15
Physical laws governing electric and magnetic fieldsFaraday’s Law (1830s)“Time varying magnetic fields produce electric
fields”
Physical laws governing electric and magnetic fieldsFaraday’s Law (1830s)“Time varying magnetic fields produce electric
fields”
Ampere-Maxwell Law (1870s)“Moving charge (current) and
time varying electric fields produce magnetic fields”
Ampere-Maxwell Law (1870s)“Moving charge (current) and
time varying electric fields produce magnetic fields”
Gauss’s Law (1840s)“Electric charge produces electric fields”“There is no magnetic charge”
Gauss’s Law (1840s)“Electric charge produces electric fields”“There is no magnetic charge”
© Okey Ugweje, PhD Page 16
Accelerating ChargeAccelerating ChargeAn accelerating charge produces time varying electric and
magnetic fieldsA time-varying electric field produces a time varying magnetic
fieldAnd, a time varying magnetic field produces a time-varying
electric fieldThus, propagating electromagnetic waves are producedNon-Accelerating ChargeA stationary charge produces only an electric fieldA charge moving with a constant velocity (DC current)
produces static electric and magnetic fields
An accelerating charge produces time varying electric and magnetic fields
A time-varying electric field produces a time varying magnetic field
And, a time varying magnetic field produces a time-varying electric field
Thus, propagating electromagnetic waves are producedNon-Accelerating ChargeA stationary charge produces only an electric fieldA charge moving with a constant velocity (DC current)
produces static electric and magnetic fields
© Okey Ugweje, PhD Page 17
PowerPower
where 0 is the intrinsic impedance of free spacewhere 0 is the intrinsic impedance of free space
2
( )V
P V I v a or wattsR
2 2
0
1E ( / ), , , ,
2aveP watts metersr r
0 377 ( )ohms
© Okey Ugweje, PhD Page 18
What’s a decibel (dB)?What’s a decibel (dB)?The dB scale allows us to plot a
function with a wide range of values on a readable scale
It expresses a power ratio
The dB scale allows us to plot a function with a wide range of values on a readable scale
It expresses a power ratio
10log adB
iso
PD
P
© Okey Ugweje, PhD Page 19
dB PropertiesdB PropertiesConverting from dB to Linear
Arithmetic operations using dBsMultiplication:
Division:
Raised to a power:
Converting from dB to Linear
Arithmetic operations using dBsMultiplication:
Division:
Raised to a power:
( /10)10 dBxlinearx
(linear) ;
(in dB)
x yz
x y z
(linear)
(in dB)
yx
zx y z
(linear)
(in dB)
ax y
x ay
© Okey Ugweje, PhD Page 20
Using dBsUsing dBs If the ratio is unity, you have 0 dBEach time the ratio doubles, add 3 dBEach time the ratio is reduced by 1/2, subtract 3 dBEach time the ratio increases (or decreases) by a power of 10,
add (or subtract) 10 dB
If the ratio is unity, you have 0 dBEach time the ratio doubles, add 3 dBEach time the ratio is reduced by 1/2, subtract 3 dBEach time the ratio increases (or decreases) by a power of 10,
add (or subtract) 10 dB
© Okey Ugweje, PhD Page 21
Reference AntennasReference Antennas
Difficult to build or approximate physically, but mathematically simple to describe
A popular reference for 1000 MHz & above PCS, microwave, etc.
Difficult to build or approximate physically, but mathematically simple to describe
A popular reference for 1000 MHz & above PCS, microwave, etc.
Quantity Units
Gain above Isotropic radiator dBi
Gain above Dipole reference dBd
Effective Radiated Power vs. Isotropic (watts or dBm) EIRP
ERP Effective Radiated Power vs. Dipole (watts or dBm) ERP
Isotropic radiator are truly non-directional - in 3 dimensions Isotropic radiator are truly non-directional - in 3 dimensions
Dipole Antenna
Notice that a dipolehas 2.15 dB gaincompared to anisotropic antenna.
Dipole AntennaNon-directional in 2-dimensional plane onlyCan be easily constructed, physically practicalA popular reference: below 1000 MHz
800 MHz cellular, land mobile, TV & FM
Dipole AntennaNon-directional in 2-dimensional plane onlyCan be easily constructed, physically practicalA popular reference: below 1000 MHz
800 MHz cellular, land mobile, TV & FM
© Okey Ugweje, PhD Page 22
Antenna Gain And ERP ExamplesAntenna Gain And ERP ExamplesMany wireless systems at 1900 & 800
MHz use omni antennasPatterns are usually drawn in the E-field
radiation units, based on equal power to each antenna
Typical wireless omni antenna concentrates most of its radiation toward the horizon, where users are, at the expense of sending less radiation sharply upward or downward
Wireless antenna’s maximum radiation is 12.1 dB stronger than the isotropic (thus 12.1 dBi gain), and 10 dB stronger than the dipole (so 10 dBd gain).
Many wireless systems at 1900 & 800 MHz use omni antennas
Patterns are usually drawn in the E-field radiation units, based on equal power to each antenna
Typical wireless omni antenna concentrates most of its radiation toward the horizon, where users are, at the expense of sending less radiation sharply upward or downward
Wireless antenna’s maximum radiation is 12.1 dB stronger than the isotropic (thus 12.1 dBi gain), and 10 dB stronger than the dipole (so 10 dBd gain).
© Okey Ugweje, PhD Page 23
RF/Microwave SystemsRF/Microwave Systems
Antenna ParametersAntenna Parameters
© Okey Ugweje, PhD Page 24
Directivity, Gain, & Beamwidth(How are they Related?)
Directivity, Gain, & Beamwidth(How are they Related?)
DirectivityDirectivity, D(θ,φ), describes the angular variation in an
antenna’s ability to efficiently transmit or receive plane waves
DirectivityDirectivity, D(θ,φ), describes the angular variation in an
antenna’s ability to efficiently transmit or receive plane waves
Therefore, Dmax is the ratio of the max power intensity radiated by directive antennas to that radiated by isotropic antennas radiating the same total power.
Therefore, Dmax is the ratio of the max power intensity radiated by directive antennas to that radiated by isotropic antennas radiating the same total power.
Maximum Directivity Maximum Directivity
max
max
Maximum radiation intensity watts/steradian
Average radiation intensity in watts/steradian
I
/ 4t
D
P
© Okey Ugweje, PhD Page 25
Expression for Maximum Directivity
where A/2 is the area of the antenna aperture in 2 and is the aperture efficiency factor
If the power is uniformly distributed across the array and there are no amplitude or phase errors, =1, otherwise <1
The effective aperture area Ae = A
This is the equivalent area of a uniformly distributed aperture that has the same directivity and beamwidth
Expression for Maximum Directivity
where A/2 is the area of the antenna aperture in 2 and is the aperture efficiency factor
If the power is uniformly distributed across the array and there are no amplitude or phase errors, =1, otherwise <1
The effective aperture area Ae = A
This is the equivalent area of a uniformly distributed aperture that has the same directivity and beamwidth
© Okey Ugweje, PhD Page 26
Antenna GainAntenna Gain Antennas are passive devices: they do not produce
powerCan only receive power in one form and pass it on in
another, minus incidental lossesCannot generate power or “amplify”
However, an antenna can appear to have “gain” compared against another antenna or condition. This gain can be expressed in dB or as a power ratio. It applies both to radiating and receiving
A directional antenna, in its direction of maximum radiation, appears to have “gain” compared against a non-directional antenna
Gain in one direction comes at the expense of less radiation in other directions
Antennas are passive devices: they do not produce powerCan only receive power in one form and pass it on in
another, minus incidental lossesCannot generate power or “amplify”
However, an antenna can appear to have “gain” compared against another antenna or condition. This gain can be expressed in dB or as a power ratio. It applies both to radiating and receiving
A directional antenna, in its direction of maximum radiation, appears to have “gain” compared against a non-directional antenna
Gain in one direction comes at the expense of less radiation in other directions
Omni-directionalAntenna
DirectionalAntenna
Antenna Gain is RELATIVE, not ABSOLUTEWhen describing antenna “gain”, the comparison
condition must be stated or implied
© Okey Ugweje, PhD Page 27
By definition, the Gain of an antenna is:
where Pin is the total power into the antenna
Therefore, Gmax is a ratio of the maximum power intensity radiated by directive antenna to that radiated by a lossless isotropic antenna radiating the same input power
The gain of an antenna can be approximated by:
By definition, the Gain of an antenna is:
where Pin is the total power into the antenna
Therefore, Gmax is a ratio of the maximum power intensity radiated by directive antenna to that radiated by a lossless isotropic antenna radiating the same input power
The gain of an antenna can be approximated by:
max
max
Maximum radiation intensity watts/steradian
Radiation intensity of a isotropic with the same input power
I
/ 4in
G
P
© Okey Ugweje, PhD Page 28
Determination of GainDetermination of Gain
Apply the same input power to a lossless isotropic antennaMeasure power received from bothThe difference of the measurement is the gain (P2 - P1)
Apply the same input power to a lossless isotropic antennaMeasure power received from bothThe difference of the measurement is the gain (P2 - P1)
© Okey Ugweje, PhD Page 29
Low vs. High Gain AntennasLow vs. High Gain AntennasThe Gain of an antenna can be approximated by
Antennas with gain < 20 dBi is said to be a low gain antenna
The Gain of an antenna can be approximated by
Antennas with gain < 20 dBi is said to be a low gain antenna
2
4AreaGain
© Okey Ugweje, PhD Page 30
How Antennas Achieve GainHow Antennas Achieve Gain Quasi-Optical Techniques (reflection, focusing)
Reflectors can be used to concentrate radiation technique works best at microwave
frequencies, where reflectors are smallExamples:
corner reflector used at cellular or higher frequencies
parabolic reflector used at microwave frequencies
grid or single pipe reflector for cellular Array techniques (discrete elements)
Power is fed or coupled to multiple antenna elements; each element radiates
Elements’ radiation in phase in some directions In other directions, a phase delay for each
element creates pattern lobes and nulls
Quasi-Optical Techniques (reflection, focusing)Reflectors can be used to concentrate radiation
technique works best at microwave frequencies, where reflectors are small
Examples:corner reflector used at cellular or higher
frequenciesparabolic reflector used at microwave
frequenciesgrid or single pipe reflector for cellular
Array techniques (discrete elements)Power is fed or coupled to multiple antenna
elements; each element radiatesElements’ radiation in phase in some directions In other directions, a phase delay for each
element creates pattern lobes and nulls
© Okey Ugweje, PhD Page 31
Directivity vs Gain Directivity vs Gain Directivity is a ratio of the power radiated by the antenna with
respect to an isotropic antenna radiating the same powerGain is a ratio of the power radiated by an antenna with respect
to a lossless isotropic antenna with the same input power
Directivity is a ratio of the power radiated by the antenna with respect to an isotropic antenna radiating the same power
Gain is a ratio of the power radiated by an antenna with respect to a lossless isotropic antenna with the same input power
The gain of an antenna is the directivity minus the losses in the antenna
The gain of an antenna is the directivity minus the losses in the antenna
The gain of an array with distributed sources can be confusing, but directivity is not
The gain of an array with distributed sources can be confusing, but directivity is not
© Okey Ugweje, PhD Page 32
Antenna BeamsAntenna Beams
© Okey Ugweje, PhD Page 33
Beamwidth Beamwidth
© Okey Ugweje, PhD Page 34
Directivity & BeamwidthDirectivity & BeamwidthSmall antennas can
coherently add contributions over a wide angular range, but since they collect energy over a small area, the maximum directivity is small
Small antennas can coherently add contributions over a wide angular range, but since they collect energy over a small area, the maximum directivity is small
Large antennas have high directivity because they sum the contributions over a large area but they can only do this over a small angular region
Large antennas have high directivity because they sum the contributions over a large area but they can only do this over a small angular region
small large
© Okey Ugweje, PhD Page 35
Beamwidth & DirectivityBeamwidth & Directivity
For an isotropic antenna, the area of the beam is 4 steradians and Dmax = 1.0
For an isotropic antenna, the area of the beam is 4 steradians and Dmax = 1.0
For a directive antenna, area of the beam is ΨxΨy and Dmax = 4LxLy /2 or Dmax = 4/ ΨxΨy
For a directive antenna, area of the beam is ΨxΨy and Dmax = 4LxLy /2 or Dmax = 4/ ΨxΨy
Note:The maximum directivity can
be expressed as the ratio of the steradian area of the beam of an isotropic antenna to the area of the main beam of the directive antenna
The directivity of an antenna is inversely related to the area of it’s main beam. Therefore, you can not have a wide beamwidth and high directivity at the same time
Note:The maximum directivity can
be expressed as the ratio of the steradian area of the beam of an isotropic antenna to the area of the main beam of the directive antenna
The directivity of an antenna is inversely related to the area of it’s main beam. Therefore, you can not have a wide beamwidth and high directivity at the same time
Ly
Lx
© Okey Ugweje, PhD Page 36
Antenna PolarizationAntenna Polarization The orientation of the electric field
component of the antenna is called its polarization.
RF current in a conductor causes EM fields that seek to induce current flowing in the same direction in other conductors.
Coupling between two antennas is proportional to the cosine of the angle of their relative orientation
The orientation of the electric field component of the antenna is called its polarization.
RF current in a conductor causes EM fields that seek to induce current flowing in the same direction in other conductors.
Coupling between two antennas is proportional to the cosine of the angle of their relative orientation
To intercept significant energy, a receiving antenna must be oriented parallel to the transmitting antennaA receiving antenna oriented at right angles to the transmitting antenna
is “cross-polarized”; will have very little current inducedVertical polarization is the default convention in wireless telephony In the cluttered urban environment, energy becomes scattered and “de-
polarized” during propagation, so polarization is not as criticalHandset users hold the antennas at seemingly random angles…..
To intercept significant energy, a receiving antenna must be oriented parallel to the transmitting antennaA receiving antenna oriented at right angles to the transmitting antenna
is “cross-polarized”; will have very little current inducedVertical polarization is the default convention in wireless telephony In the cluttered urban environment, energy becomes scattered and “de-
polarized” during propagation, so polarization is not as criticalHandset users hold the antennas at seemingly random angles…..
© Okey Ugweje, PhD Page 37
Size of an AntennaSize of an AntennaThe size of an antenna depends on the type of antenna! The size of an antenna depends on the type of antenna!
Suppose you needs an antenna with 15 dBi gain?
it would have to have an ideal square aperture of at least:
Suppose you needs an antenna with 15 dBi gain?
it would have to have an ideal square aperture of at least:
At 38 GHz (new LMDS band), the antenna would be ~ 0.5 in2
At 750 kHz (750-AM, radio), the antenna would be at least 24,965 in2 (4/10ths of a mile)
At 38 GHz (new LMDS band), the antenna would be ~ 0.5 in2
At 750 kHz (750-AM, radio), the antenna would be at least 24,965 in2 (4/10ths of a mile)
2
2 2
4
15dBi2.517
4
AreaGain
Area
© Okey Ugweje, PhD Page 38
RF/Microwave Systems RF/Microwave Systems
Antenna RadiationAntenna Radiation
© Okey Ugweje, PhD Page 39
Radiation PatternsRadiation PatternsAntennas are designed to deliberately direct or minimize
radiation in different angular regionsAntennas can be designed to have:Omni-directional radiation patternsSectoral radiation patternsHigh gain patternsSidelobe control and/or beam shaping
Antennas are designed to deliberately direct or minimize radiation in different angular regions
Antennas can be designed to have:Omni-directional radiation patternsSectoral radiation patternsHigh gain patternsSidelobe control and/or beam shaping
Omni-Directional Radiation PatternAn Omni antenna has a constant 0 dBi
pattern in all directionsAn Omni pattern is what would be
generated by an isotropic antenna
Omni-Directional Radiation PatternAn Omni antenna has a constant 0 dBi
pattern in all directionsAn Omni pattern is what would be
generated by an isotropic antenna
In reality there are no isotropic antennas - but there are some designs that come close
In reality there are no isotropic antennas - but there are some designs that come close
© Okey Ugweje, PhD Page 40
Sectoral Radiation PatternSectoral Radiation PatternSectoral radiation patterns are designed to provide beam
coverage within certain angular sectors and reject signals from other angular sectorsThese are used for point to region coverageGains are typically in range of 3 dBi to 20 dBi, dependent
upon the size of the sector coverage (beamwidth) desired
Sectoral radiation patterns are designed to provide beam coverage within certain angular sectors and reject signals from other angular sectorsThese are used for point to region coverageGains are typically in range of 3 dBi to 20 dBi, dependent
upon the size of the sector coverage (beamwidth) desired
Cell towers often has 3 faces for mounting three antennas with 120° azimuth beamwidths
© Okey Ugweje, PhD Page 41
SidelobesSidelobesSidelobes are very important in Antenna EngineeringSidelobes are very important in Antenna Engineering
© Okey Ugweje, PhD Page 42
Referencing Sidelobe LevelsReferencing Sidelobe Levels
1st sidelobe is +17 dB with respect to isotropic
1st sidelobe is +17 dB with respect to isotropic
1st sidelobe is -13 dB with respect to the main beam
1st sidelobe is -13 dB with respect to the main beam
© Okey Ugweje, PhD Page 43
Average Sidelobe Levels Average Sidelobe Levels
SLave is the average sidelobe level wrt isotropic
PS is power in sidelobe region Pt is the total power radiated Pmainbeam is power in the main beam s is the steradian area of the
sidelobes mainbeam is the steradian area of the
main beam
SLave is the average sidelobe level wrt isotropic
PS is power in sidelobe region Pt is the total power radiated Pmainbeam is power in the main beam s is the steradian area of the
sidelobes mainbeam is the steradian area of the
main beam
NoteThe average isotropic sidelobe level is just 1 minus the
fractional power in the main beamTherefore, anything you do that takes power from the main
beam, raises the average sidelobe level
NoteThe average isotropic sidelobe level is just 1 minus the
fractional power in the main beamTherefore, anything you do that takes power from the main
beam, raises the average sidelobe level
4save
t
PSL
P
4
4s mainbeam
avemainbeam t
P PSL
P
1 ( / )
1 ( / 4 )mainbeam t
avemainbeam
P PSL
1 mainbeamave
t
PSL
P
© Okey Ugweje, PhD Page 44
Basic Antenna Radiation Patterns Parameters
Basic Antenna Radiation Patterns Parameters
© Okey Ugweje, PhD Page 45
Basic Antenna Radiation Patterns Parameters
Basic Antenna Radiation Patterns Parameters
Beam PeakRegion of maximum response, usually a measurement of
Gain (dB relative to isotropic radiator)Main LobeThe “business end” of the antenna, angular area of highest
response 1st Side LobeThe sidelobe nearest to the beam peak, a function of
antenna design illumination taper (energy distribution)Null DepthThe pattern phase reverses 180º, usually an indication of
focusVSWR voltage standing wave ratio, commonly measured as return
loss (dB)
Beam PeakRegion of maximum response, usually a measurement of
Gain (dB relative to isotropic radiator)Main LobeThe “business end” of the antenna, angular area of highest
response 1st Side LobeThe sidelobe nearest to the beam peak, a function of
antenna design illumination taper (energy distribution)Null DepthThe pattern phase reverses 180º, usually an indication of
focusVSWR voltage standing wave ratio, commonly measured as return
loss (dB)
© Okey Ugweje, PhD Page 46
© Okey Ugweje, PhD Page 47
Effective Radiated PowerEffective Radiated PowerAn antenna radiates all power fed to it
from the transmitter, minus any incidental losses
Every direction gets some amount of power
Effective Radiated Power (ERP) is the apparent power in a particular directionEqual to the actual transmitter power
times antenna gain in that directionEffective Radiated Power is expressed in
comparison to a standard radiatorERP: compared with dipole antennaEIRP: compared with Isotropic
antenna
An antenna radiates all power fed to it from the transmitter, minus any incidental losses
Every direction gets some amount of power
Effective Radiated Power (ERP) is the apparent power in a particular directionEqual to the actual transmitter power
times antenna gain in that directionEffective Radiated Power is expressed in
comparison to a standard radiatorERP: compared with dipole antennaEIRP: compared with Isotropic
antenna
© Okey Ugweje, PhD Page 48
Example:
Antennas A and B each radiate 100 watts from their own transmitters
Antenna A is our referenceAntenna B is directional. In its maximum direction, its signal
seems 2.75 stronger than the signal from antenna AAntenna B’s ERP in this case is 275 watts.
© Okey Ugweje, PhD Page 49
Radiation PatternsKey Features And Terminology
Radiation PatternsKey Features And Terminology
An antenna’s directivity is expressed as a series of patterns
Horizontal Plane Pattern graphs the radiation as a function of azimuth (i.e., direction N-E-S-W)
Vertical Plane Pattern graphs the radiation as a function of elevation (i.e., up, down, horizontal)
An antenna’s directivity is expressed as a series of patterns
Horizontal Plane Pattern graphs the radiation as a function of azimuth (i.e., direction N-E-S-W)
Vertical Plane Pattern graphs the radiation as a function of elevation (i.e., up, down, horizontal)
Typical ExampleHorizontal Plane Pattern
Antennas are often compared by noting specific landmark points on their patterns: -3 dB (“HPBW”), -6 dB, -10 dB pointsFront-to-back ratioAngles of nulls, minor lobes, etc.
Antennas are often compared by noting specific landmark points on their patterns: -3 dB (“HPBW”), -6 dB, -10 dB pointsFront-to-back ratioAngles of nulls, minor lobes, etc.
© Okey Ugweje, PhD Page 50
Other Possible LossesOther Possible LossesPolarization mismatchAntenna angular alignmentRain or other atmospheric effectsTransmission line lossesRefractionAtmospheric losses are larger for low elevation angles
Polarization mismatchAntenna angular alignmentRain or other atmospheric effectsTransmission line lossesRefractionAtmospheric losses are larger for low elevation angles
© Okey Ugweje, PhD Page 51
What is Bandwidth? What is Bandwidth? In communication systems it sets the data transmission rate
and in radar the bandwidth determines the range resolution In communication systems it sets the data transmission rate
and in radar the bandwidth determines the range resolution
Antenna carrier frequency is f0, but if data is transmitted or received, the antenna will have to support a signal bandwidth of f0 ± ∆f/2.
Antenna may also have to support a tunable bandwidth where the f0 is tuned or changed
Antenna is required to transmit and receive EM energy over the signal bandwidth without any adjustments. However, it is possible make adjustments when the tunable bandwidth is changed
Antenna carrier frequency is f0, but if data is transmitted or received, the antenna will have to support a signal bandwidth of f0 ± ∆f/2.
Antenna may also have to support a tunable bandwidth where the f0 is tuned or changed
Antenna is required to transmit and receive EM energy over the signal bandwidth without any adjustments. However, it is possible make adjustments when the tunable bandwidth is changed
1Hz
22 m
1Bit Rate = Hertz
f
cr c
f
f
© Okey Ugweje, PhD Page 52
Antenna ImpedanceAntenna Impedance
Everything has an impedance, Z: Everything has an impedance, Z:
Where the real component, R, is the radiation resistance and the imaginary component, X, is the reactance
Where the real component, R, is the radiation resistance and the imaginary component, X, is the reactance
Reactance can be either:inductive (like an inductor) or capacitive (like a capacitor)
Reactance can be either:inductive (like an inductor) or capacitive (like a capacitor)
Even air or a vacuum has an impedance – the characteristic impedance of free space:
Even air or a vacuum has an impedance – the characteristic impedance of free space:
© Okey Ugweje, PhD Page 53
Power Transfer & Antenna ResonancePower Transfer & Antenna Resonance
For maximum power transfer,
Rantenna = System Z0
jX = 0.0
For maximum power transfer,
Rantenna = System Z0
jX = 0.0
In addition to the standing wave phenomenon, Resonance also describes the impedance response of a structure where:
the reactance goes to zero at a particular frequency
In addition to the standing wave phenomenon, Resonance also describes the impedance response of a structure where:
the reactance goes to zero at a particular frequency
Generally, the most striking resonances occur when an antenna is electrically small - in the neighborhood of a wavelength in size (fundamental and lower order harmonics)
Generally, the most striking resonances occur when an antenna is electrically small - in the neighborhood of a wavelength in size (fundamental and lower order harmonics)
Some antennas have resonances at 0.25λ, 0.50λ, 0.75λ, λ, etc.
and some have resonances at 0.50λ, 1λ, 1.5λ, 2λ, etc.
© Okey Ugweje, PhD Page 54
RF/Microwave SystemsRF/Microwave Systems
Types of AntennasTypes of Antennas
© Okey Ugweje, PhD Page 55
Low Gain Antennas/ApplicationsLow Gain Antennas/Applications
Electrically Small Wire Antennas - Sub-resonant LoopsOften referred to as “Magnetic
Antennas” conceptualize as coupling to the magnetic B-field
VLF, UHFSub-resonant Wire Antennas E.g., Small Coils, Ferrite Loaded
Coils, Resonant Loop AntennasMicrostrip Antennas
Electrically Small Wire Antennas - Sub-resonant LoopsOften referred to as “Magnetic
Antennas” conceptualize as coupling to the magnetic B-field
VLF, UHFSub-resonant Wire Antennas E.g., Small Coils, Ferrite Loaded
Coils, Resonant Loop AntennasMicrostrip Antennas
Low Gain Antennas are OMNI - to - MODERATELY DIRECTIONAL ANTENNA PATTERNS
© Okey Ugweje, PhD Page 56
Resonant Wire Antennas - MonopoleCellular, PCS, FM car radio, wireless
handsets, etc
Resonant Wire Antennas - MonopoleCellular, PCS, FM car radio, wireless
handsets, etc
Resonant Wire Antennas - DipoleCellular, PCS, FM receiver, etc
Resonant Wire Antennas - DipoleCellular, PCS, FM receiver, etc
Horn AntennasHorn Antennas
Single Column ArraySingle Column Array
© Okey Ugweje, PhD Page 57
Collinear vertical arraysEssentially omni-directional in
horizontal planePower gain approximately equal to
the number of elementsNulls exist in vertical pattern, unless
deliberately filled Arrays in horizontal planeDirectional in horizontal plane:
useful for sectorizationYagi-Uda Arraysone driven element, parasitic
coupling to othersLog-periodicall elements driven/wide bandwidt
Collinear vertical arraysEssentially omni-directional in
horizontal planePower gain approximately equal to
the number of elementsNulls exist in vertical pattern, unless
deliberately filled Arrays in horizontal planeDirectional in horizontal plane:
useful for sectorizationYagi-Uda Arraysone driven element, parasitic
coupling to othersLog-periodicall elements driven/wide bandwidt
© Okey Ugweje, PhD Page 58
Collinear Vertical ArraysCollinear Vertical ArraysFor the family of omni-
directional wireless antennas:No. of elements determinesPhysical size & GainBeamwidth, first null angle
Models with many elements have very narrow beamwidthsRequire stable mounting
and careful alignmentWatch out: be sure nulls do
not fall in important coverage areas
Rod and grid reflectors are sometimes added for mild directivity
For the family of omni-directional wireless antennas:
No. of elements determinesPhysical size & GainBeamwidth, first null angle
Models with many elements have very narrow beamwidthsRequire stable mounting
and careful alignmentWatch out: be sure nulls do
not fall in important coverage areas
Rod and grid reflectors are sometimes added for mild directivity
Vertical Plane Pattern
© Okey Ugweje, PhD Page 59
© Okey Ugweje, PhD Page 60
High Gain or Aperture AntennasHigh Gain or Aperture Antennas
High Gain Antennas are characterized by:Narrow BeamNarrow spatial filter or “radio wave telescope”Tracking targetsPoint-to-point communication
Power ConcentrationDetection of weak signalsTransmission/reception over long distances
Used to provide small “pencil beams” to concentrate the antenna field of view to a small angular region
High Gain Antennas are characterized by:Narrow BeamNarrow spatial filter or “radio wave telescope”Tracking targetsPoint-to-point communication
Power ConcentrationDetection of weak signalsTransmission/reception over long distances
Used to provide small “pencil beams” to concentrate the antenna field of view to a small angular region
High Gain Antennas areDIRECTIVE - to - HIGHLY DIRECTIVE ANTENNA PATTERNS
© Okey Ugweje, PhD Page 61
High Gain Antenna TypesReflectors - Microwave/Satellite linksLenses - Luneberg, Rotman, Fresnel, DielectricArrays - Fixed beam, scanning beam
High Gain Antenna TypesReflectors - Microwave/Satellite linksLenses - Luneberg, Rotman, Fresnel, DielectricArrays - Fixed beam, scanning beam
Gains are typically in the range of > 30 dBi, with beamwidths on the order of a few degrees or smaller
Antenna design is meanly of the Prime Focus Reflector typeArray Antennas can also be used to obtain high gain
Gains are typically in the range of > 30 dBi, with beamwidths on the order of a few degrees or smaller
Antenna design is meanly of the Prime Focus Reflector typeArray Antennas can also be used to obtain high gain
These are used for fixed point to point communications, object sensing and tracking
These are used for fixed point to point communications, object sensing and tracking
© Okey Ugweje, PhD Page 62
© Okey Ugweje, PhD Page 63
Sample High Gain AntennasSample High Gain Antennas
© Okey Ugweje, PhD Page 64
Near-Field vs. Far-FieldNear-Field vs. Far-Field Antenna behavior is very different close-in and far
out Near-field region:
The area within about 10 times the spacing between antenna’s internal elements Inside this region, the signal behaves as
independent fields from each element of the antenna, with their individual directivity
Far-field region: The area beyond roughly 10 times the spacing
between the antenna’s internal elementsIn this region, the antenna seems to be a point-
source and the contributions of the individual elements are indistinguishable
The pattern is the composite of the array
Antenna behavior is very different close-in and far out
Near-field region: The area within about 10 times the spacing
between antenna’s internal elements Inside this region, the signal behaves as
independent fields from each element of the antenna, with their individual directivity
Far-field region: The area beyond roughly 10 times the spacing
between the antenna’s internal elementsIn this region, the antenna seems to be a point-
source and the contributions of the individual elements are indistinguishable
The pattern is the composite of the array
Obstructions in the near-field can dramatically alter the antenna performance
© Okey Ugweje, PhD Page 65
Local Obstruction at a SiteLocal Obstruction at a SiteObstructions near the site are sometimes unavoidable Near-field obstructions can seriously alter pattern shapeMore distant local obstructions can cause severe blockage, as
for example roof edge in the figure at rightKnife-edge diffraction analysis can help estimate
diffraction loss in these situationsExplore other antenna mounting positions
Obstructions near the site are sometimes unavoidable Near-field obstructions can seriously alter pattern shapeMore distant local obstructions can cause severe blockage, as
for example roof edge in the figure at rightKnife-edge diffraction analysis can help estimate
diffraction loss in these situationsExplore other antenna mounting positions
Local obstruction example
© Okey Ugweje, PhD Page 66
Isolation Between AntennasIsolation Between AntennasOften multiple antennas are needed at a site and
interaction is troublesomeElectrical isolation between antennas
Coupling loss between isotropic antennas one wavelength apart is 22 dB
6 dB additional coupling loss with each doubling of separation
Add gain or loss referenced from horizontal plane patterns
Measure vertical separation between centers of the antennasvertical separation usually is very effective
One antenna should not be mounted in main lobe and near-field of anotherTypically within 10 feet @ 800 MHzTypically 5-10 feet @ 1900 MHz
Often multiple antennas are needed at a site and interaction is troublesome
Electrical isolation between antennasCoupling loss between isotropic antennas one
wavelength apart is 22 dB6 dB additional coupling loss with each doubling of
separationAdd gain or loss referenced from horizontal plane
patternsMeasure vertical separation between centers of the
antennasvertical separation usually is very effective
One antenna should not be mounted in main lobe and near-field of anotherTypically within 10 feet @ 800 MHzTypically 5-10 feet @ 1900 MHz
© Okey Ugweje, PhD Page 67
Arrays often used in Cellular and Sectoring
Arrays often used in Cellular and Sectoring
Macrocellular range of several km
Microcellular range of several km
Common implementation uses 3 sectors as “cells”
These low gain antennas usually have ±60°azimuth
In-building
Picocell Microcell Macrocell Magacell
Urban
Suburban
Global
© Okey Ugweje, PhD Page 68
The Goal of Antenna DowntiltThe Goal of Antenna Downtilt
Downtilt is commonly used for two reasons
1. Reduce InterferenceReduce radiation toward a distant
co-channel cellConcentrate radiation within the
serving cell
Downtilt is commonly used for two reasons
1. Reduce InterferenceReduce radiation toward a distant
co-channel cellConcentrate radiation within the
serving cell
2. Prevent “overshoot”Improve coverage of nearby
targets far below the antenna–otherwise within “null” of antenna pattern
2. Prevent “overshoot”Improve coverage of nearby
targets far below the antenna–otherwise within “null” of antenna pattern
Depression or downtilt of an antenna is the process of redirecting the antenna beam downwards
Depression or downtilt of an antenna is the process of redirecting the antenna beam downwards
© Okey Ugweje, PhD Page 69
Vertical Depression AnglesVertical Depression Angles Basic principle:
Important to match vertical pattern against intended coverage targetsCompare the angles toward
objects against the antenna vertical pattern
what’s radiating toward the target?
Don’t position a null of the antenna toward an important coverage target!
Sketch and formulateNotice the height and horizontal
distance must be expressed in the same units before dividing (both in feet, both in miles, etc.)
Basic principle: Important to match vertical pattern
against intended coverage targetsCompare the angles toward
objects against the antenna vertical pattern
what’s radiating toward the target?
Don’t position a null of the antenna toward an important coverage target!
Sketch and formulateNotice the height and horizontal
distance must be expressed in the same units before dividing (both in feet, both in miles, etc.)
-1 vertical distance= tan
horizontal distance
© Okey Ugweje, PhD Page 70
Types Of DowntiltTypes Of Downtilt
Mechanical downtiltPhysically tilt the antennaThe pattern in front goes down,
and behind goes upPopular for sectorization and
special omni applicationsElectrical downtiltIncremental phase shift is applied
in the feed networkThe pattern “droops” all around,
like an inverted saucerCommon technique when
downtilting omni cells
Mechanical downtiltPhysically tilt the antennaThe pattern in front goes down,
and behind goes upPopular for sectorization and
special omni applicationsElectrical downtiltIncremental phase shift is applied
in the feed networkThe pattern “droops” all around,
like an inverted saucerCommon technique when
downtilting omni cells
© Okey Ugweje, PhD Page 71
Reduce Interference - Scenario 1Reduce Interference - Scenario 1The Concept:Radiate a strong signal toward
everything within the serving cell, but significantly reduce radiation toward the area of Cell B
The Concept:Radiate a strong signal toward
everything within the serving cell, but significantly reduce radiation toward the area of Cell B
The Reality:When actually calculated, it’s
surprising how small the difference in angle is between the far edge of cell A and the near edge of Cell BDelta in the example is only 0.3o!!Let’s look at antenna pattern
The Reality:When actually calculated, it’s
surprising how small the difference in angle is between the far edge of cell A and the near edge of Cell BDelta in the example is only 0.3o!!Let’s look at antenna pattern
© Okey Ugweje, PhD Page 72
It’s an attractive idea, but usually the
angle between edge of serving cell and nearest edge of distant cell is just too small to exploitDowntilt or not, can’t get much
difference in antenna radiation between θ1 and θ2
Even if the pattern were sharp enough, alignment accuracy and wind-flexing would be problemsθ in this example is < 1o!
Also, if downtilting -- watch out for excessive RSSI and IM involving mobiles near cell!
Soft handoff and good CDMA power control is more important
It’s an attractive idea, but usually the angle between edge of serving cell and nearest edge of distant cell is just too small to exploitDowntilt or not, can’t get much
difference in antenna radiation between θ1 and θ2
Even if the pattern were sharp enough, alignment accuracy and wind-flexing would be problemsθ in this example is < 1o!
Also, if downtilting -- watch out for excessive RSSI and IM involving mobiles near cell!
Soft handoff and good CDMA power control is more important
© Okey Ugweje, PhD Page 73
Avoid Overshoot - Scenario 2Avoid Overshoot - Scenario 2Application concern: too little radiation
toward low, close-in coverage targetsThe solution is common-sense matching
of the antenna vertical pattern to the angles where radiation is neededCalculate vertical angles to targets!!Watch the pattern nulls--where do
they fall on the ground?Choose a low-gain antenna with a fat
vertical pattern if you have a wide range of vertical angles to “hit”
Downtilt if appropriateIf needed, investigate special “null-
filled” antennas with smooth patterns
Application concern: too little radiation toward low, close-in coverage targets
The solution is common-sense matching of the antenna vertical pattern to the angles where radiation is neededCalculate vertical angles to targets!!Watch the pattern nulls--where do
they fall on the ground?Choose a low-gain antenna with a fat
vertical pattern if you have a wide range of vertical angles to “hit”
Downtilt if appropriateIf needed, investigate special “null-
filled” antennas with smooth patterns
© Okey Ugweje, PhD Page 74
Other Antenna Selection Considerations
Other Antenna Selection Considerations
Before choosing an antenna for widespread deployment, investigate the following:
Manufacturer’s measured patternsObserve pattern at low end of band, mid-band, and high end
of bandAny troublesome back lobes or minor lobes in H or V
patterns?Watch out for nulls which would fall toward populated areasBe suspicious of extremely symmetrical, “clean” measured
patternsObtain Intermodulation Specifications and test results (-130
or better)
Before choosing an antenna for widespread deployment, investigate the following:
Manufacturer’s measured patternsObserve pattern at low end of band, mid-band, and high end
of bandAny troublesome back lobes or minor lobes in H or V
patterns?Watch out for nulls which would fall toward populated areasBe suspicious of extremely symmetrical, “clean” measured
patternsObtain Intermodulation Specifications and test results (-130
or better)
© Okey Ugweje, PhD Page 75
Inspect return loss measurements across the band
Inspect a sample unitPhysical integrity? weatherproof?Dissimilar metals in contact anywhere?Collinear vertical antennas: feed method? End (compromise) or center-fed (best)?Complete your own return loss measurements, if possibleIdeally, do your own limited pattern verification
Check with other users for their experiences
Inspect return loss measurements across the band Inspect a sample unitPhysical integrity? weatherproof?Dissimilar metals in contact anywhere?Collinear vertical antennas: feed method? End (compromise) or center-fed (best)?Complete your own return loss measurements, if possibleIdeally, do your own limited pattern verification
Check with other users for their experiences
© Okey Ugweje, PhD Page 76
Antenna ApplicationsAntenna ApplicationsTransmission lines, Antennas and Scatterers, provide an EM or
RF link where information/intelligence is exchanged or detected An antenna can be the first or last element of a system
implementation Antennas serve as the interface to a free space interconnected
environment in which the tethers can be removed allowing mobility and remote placement or detection of objects within a three dimensional environment
An antenna alone can serve no purpose, but must be an integral part of a system design to accomplish a specific purpose
These purposes can include but are not limited to:Communication Systems
as in free space propagation links (data, command, control, broadcast, voice, etc.)
Transmission lines, Antennas and Scatterers, provide an EM or RF link where information/intelligence is exchanged or detected
An antenna can be the first or last element of a system implementation
Antennas serve as the interface to a free space interconnected environment in which the tethers can be removed allowing mobility and remote placement or detection of objects within a three dimensional environment
An antenna alone can serve no purpose, but must be an integral part of a system design to accomplish a specific purpose
These purposes can include but are not limited to:Communication Systems
as in free space propagation links (data, command, control, broadcast, voice, etc.)
© Okey Ugweje, PhD Page 77
Some Basic Antenna ApplicationsSome Basic Antenna Applications Fixed Services
Point to Point, Point to Multipoint, backhaul Mobile Services
Paging, Cellular, Trunked Radio, Maritime Mobile
Fixed ServicesPoint to Point, Point to Multipoint, backhaul
Mobile ServicesPaging, Cellular, Trunked Radio, Maritime Mobile
RadiodeterminationGPS, Radar, ILS, LORAN-C
BroadcastingRadio, TV, Direct-Broadcast Sat. (DBS), TVRO (Receive Only)
Safety (emergency and distress) ServicesPolice, Fire, National Weather Service (NWS)
Vehicular, Land, Sea, Air and SpaceCommunications, Navigation, Collision Avoidance, Imaging
Building MountedCellular, WLAN, Bluetooth, Wi Fi (IEEE 802.11)
CommercialRF tagging, Automatic toll, Process monitoring, Remote control
RadiodeterminationGPS, Radar, ILS, LORAN-C
BroadcastingRadio, TV, Direct-Broadcast Sat. (DBS), TVRO (Receive Only)
Safety (emergency and distress) ServicesPolice, Fire, National Weather Service (NWS)
Vehicular, Land, Sea, Air and SpaceCommunications, Navigation, Collision Avoidance, Imaging
Building MountedCellular, WLAN, Bluetooth, Wi Fi (IEEE 802.11)
CommercialRF tagging, Automatic toll, Process monitoring, Remote control
© Okey Ugweje, PhD Page 78
sensors as in direction finding, field measurements, radar,
weather/meteorology and environmental detectionPublic SafetyWeather alertEmergency servicesLocal Law Enforcement
Transportation (Aviation)Air Traffic ControlNavigationEmergency Locator Transmitter
Military/DefenseMany applications here
sensors as in direction finding, field measurements, radar,
weather/meteorology and environmental detectionPublic SafetyWeather alertEmergency servicesLocal Law Enforcement
Transportation (Aviation)Air Traffic ControlNavigationEmergency Locator Transmitter
Military/DefenseMany applications here
© Okey Ugweje, PhD Page 79
Weather Antenna ExampleWeather Antenna Example
© Okey Ugweje, PhD Page 80
Airport Antenna ExampleAirport Antenna Example
© Okey Ugweje, PhD Page 81
Antenna Performance IssuesAntenna Performance Issues
Electrical ParametersFrequency
Bandwidth Fixed/TunableGain/Directivity
Omni-directionalSectoralSidelobe SpecificationsFront-Back Ratio
Power HandlingAveragePeak
Electrical ParametersFrequency
Bandwidth Fixed/TunableGain/Directivity
Omni-directionalSectoralSidelobe SpecificationsFront-Back Ratio
Power HandlingAveragePeak
Mechanical ParametersConstructionSizeWeightEnvironmentHeating/Cooling
Mechanical ParametersConstructionSizeWeightEnvironmentHeating/Cooling
Antenna performance is limited by the physical/mechanical design and operational frequency
Likewise, antenna performance is strongly coupled to the environment in which it must operate
Antenna performance is limited by the physical/mechanical design and operational frequency
Likewise, antenna performance is strongly coupled to the environment in which it must operate
© Okey Ugweje, PhD Page 82
Basic Antenna PerformanceBasic Antenna PerformanceAntennas are typically designed to provide point to point links,
or area coverageThe frequency of operation impacts performance of these
systems. At lower frequencies such as HF, radio waves propagate through the ionosphere and well beyond the horizon of the earth
As the frequency is increased, (VHF, UHF and Microwave), the waves tend to propagate primarily in a line of site (LOS) mode
Also, the shorter the wavelength or the higher the frequency, there is increased space loss of the transmitted wave. These features can and tend to severely impact antenna placement.
Antennas are typically designed to provide point to point links, or area coverage
The frequency of operation impacts performance of these systems. At lower frequencies such as HF, radio waves propagate through the ionosphere and well beyond the horizon of the earth
As the frequency is increased, (VHF, UHF and Microwave), the waves tend to propagate primarily in a line of site (LOS) mode
Also, the shorter the wavelength or the higher the frequency, there is increased space loss of the transmitted wave. These features can and tend to severely impact antenna placement.
© Okey Ugweje, PhD Page 83
Blockage ErrorBlockage ErrorDefinition: An obstruction which blocks part of the antenna aperture
Definition: An obstruction which blocks part of the antenna aperture
Effects of BlockageReduces directivityLoss in directivity ≈ (Blockage area)/(Antenna area)
Perturbs SidelobesResulting sidelobes are generally higherA specific sidelobe may go up or down
Beamwidth generally reducedImpacts monopulse performance
Effects of BlockageReduces directivityLoss in directivity ≈ (Blockage area)/(Antenna area)
Perturbs SidelobesResulting sidelobes are generally higherA specific sidelobe may go up or down
Beamwidth generally reducedImpacts monopulse performance
© Okey Ugweje, PhD Page 84
RF/Microwave Systems RF/Microwave Systems
Antenna SitingAntenna Siting
© Okey Ugweje, PhD Page 85
Optimum LocationOptimum LocationFinding the best location for an antenna requires trial and error.We don’t have software to tell us the best antenna location.Current software barely computes performance for a given
locationThat’s because environments are so complex.
Finding the best location for an antenna requires trial and error.We don’t have software to tell us the best antenna location.Current software barely computes performance for a given
locationThat’s because environments are so complex.
For siting on terrain, one would like to model the precise contours of the terrain and a map of the constitutive parameters.
Usually this information is not available, and the terrain can be described only in statistical terms.Often there is digital terrain elevation data (DTED), but
only statistics or estimates of other parameters
For siting on terrain, one would like to model the precise contours of the terrain and a map of the constitutive parameters.
Usually this information is not available, and the terrain can be described only in statistical terms.Often there is digital terrain elevation data (DTED), but
only statistics or estimates of other parameters
© Okey Ugweje, PhD Page 86
Best approach to antenna-on-vehicle problem is model the
whole vehicleThis is not practical for vehicles more than 10 or 15
wavelengths longThus, asymptotic methods (high-frequency
approximations) are needed for most antenna siting problems on vehicles
Best approach to antenna-on-vehicle problem is model the whole vehicle
This is not practical for vehicles more than 10 or 15 wavelengths longThus, asymptotic methods (high-frequency
approximations) are needed for most antenna siting problems on vehicles
For siting within buildings or among buildings, approaches are similar to the terrain case, but sometimes full-wave solutions are possible
For siting within buildings or among buildings, approaches are similar to the terrain case, but sometimes full-wave solutions are possible
© Okey Ugweje, PhD Page 87
Satellite Up/Down LinksSatellite Up/Down Links
© Okey Ugweje, PhD Page 88
Microwave Line of Sight and Backhaul Systems
Microwave Line of Sight and Backhaul Systems
© Okey Ugweje, PhD Page 89
Passive RepeaterPassive Repeater
Passive reflectors or repeaters are used to redirect line of sight (LOS) propagation paths between fixed assets.
Passive reflectors or repeaters are used to redirect line of sight (LOS) propagation paths between fixed assets.