Presentation 3. Antenna Parameters
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Lecture 3. ANTENNA PARAMETERS
Dr Hasanovic: ADVANCED ANTENNA THEORY (Spring 2012
Properties of antennas are described through antenna parameters Antenna parameters are also used for comparing various antennaconfigurations
Antenna parameters define the performance of an antenna, from variousperspectives
Certain antenna parameters are mutually related to each other
ANTENNA PARAMETERS:[1] radiation pattern
[2] directivity[3] gain[4] efficiency[5] axial ratio[6] input impedance[7] frequency band, etc.
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Lecture 3. ANTENNA PARAMETERS
Dr Hasanovic: ADVANCED ANTENNA THEORY (Spring 2012
RADIATION PATTERN[1] this is the most important and the mostcomprehensive antenna parameter
[2] graphical representation ofelectromagnetic radiation thatcharacterizes an antenna, as a functionof three dimensional space coordinates
Field pattern:
Power pattern:
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Lecture 3. ANTENNA PARAMETERS
Dr Hasanovic: ADVANCED ANTENNA THEORY (Spring 2012
RADIATION PATTERN (cont.)
DIJAGRAM POLJA(linearna skala)
DIJAGRAM SNAGE(linearna skala)
DIJAGRAM SNAGE(logaritamska skala)
DIJAGRAM POLJA(linearna skala)
DIJAGRAM SNAGE(linearna skala)
DIJAGRAM SNAGE(logaritamska skala)
POWER RADIATION PATTERN(linear scale)
FIELD RADIATION PATTERN(linear scale)
POWER RADIATION PATTERN(logarithmic scale)
GLAVNA LEPEZA
SPOREDNE LEPEZE
POZADINSKA LEPEZA
BONA LEPEZASPOREDNE
LEPEZE
IRINA SNOPAIZMEU PRVIH NULA
(FNBW)
IRINA SNOPASA 50% SNAGE(HPBW)
GLAVNA LEPEZA
SPOREDNE LEPEZE
POZADINSKA LEPEZA
BONA LEPEZASPOREDNE
LEPEZE
IRINA SNOPAIZMEU PRVIH NULA
(FNBW)
IRINA SNOPASA 50% SNAGE(HPBW)
FIRST NULL BEAM WIDTH(FNBW)
HALF POWER BEAM WIDTH(HPBW)
MAIN LOBE (BEAM)
SIDE LOBE
BACK LOBE
MINOR LOBES
MINORLOBES
LOBE (BEAM)MAJOR LOBEMINOR LOBE
side lobeback lobe
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Lecture 3. ANTENNA PARAMETERS
Dr Hasanovic: ADVANCED ANTENNA THEORY (Spring 2012
RADIATION PATTERN (cont.)
GLAVNA LEPEZA
SPOREDNE LEPEZE
POZADINSKA LEPEZA
BONA LEPEZASPOREDNE
LEPEZE
IRINA SNOPAIZMEU PRVIH NULA
(FNBW)
IRINA SNOPASA 50% SNAGE
(HPBW)
GLAVNA LEPEZA
SPOREDNE LEPEZE
POZADINSKA LEPEZA
BONA LEPEZASPOREDNE
LEPEZE
IRINA SNOPAIZMEU PRVIH NULA
(FNBW)
IRINA SNOPASA 50% SNAGE
(HPBW)
FIRST NULL BEAM WIDTH(FNBW)
HALF POWER BEAM WIDTH(HPBW)
MAIN LOBE (BEAM)
SIDE LOBE
BACK LOBE
MINOR LOBES
MINORLOBES
The First Null Beam Width (FNBW)represents an angle between the twostraight lines with an origin in thecenter of the radiation pattern that passthrough the two points on the oppositesides of the beam characterized by thezero radiation.
The Half Power Beam Width (HPBW)is an angle between the two straightlines with the origin at the center of theradiation pattern that pass through thetwo points on the opposite sides of thebeam characterized by a radiationintensity equal to the half of theintensity present on the main axis ofthe beam (maximum intensity).
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Lecture 3. ANTENNA PARAMETERS
Dr Hasanovic: ADVANCED ANTENNA THEORY (Spring 2012
RADIATION INTENSITY
S
2
SSS
dds inr)(*)(21
d)(*)(21
d)(*)(21
d)(P
rrHrE
srHrEsrHrEsrS
The total power that an antenna radiates through a specified surface S that is apart of a sphere of radius r :
The total power that an antenna radiates through a unitspace angle d=sindd or through any other spaceangle obtained through integration of unit angles, isconstant
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Lecture 3. ANTENNA PARAMETERS
Dr Hasanovic: ADVANCED ANTENNA THEORY (Spring 2012
RADIATION INTENSITY (cont.)To avoid dependence on r, we introduce a new quantity called RADIATIONINTENSITY :
Radiation intensity is proportional to the antenna radiation pattern because it can
be shown that :
Average radiation intensity:
Coefficient 4 represents the value of thetotal space angle (units steradians)
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Lecture 3. ANTENNA PARAMETERS
Dr Hasanovic: ADVANCED ANTENNA THEORY (Spring 2012
BEAM SOLID ANGLE
The beam solid angle A physically represents a solid angle through which anantenna would radiate if its radiation intensity would have been constant and equalto the maximum value U max for all directions within the angle A.
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Lecture 3. ANTENNA PARAMETERS
Dr Hasanovic: ADVANCED ANTENNA THEORY (Spring 2012
DIRECTIVITYAntenna directivity D is defined as the ratio of the radiation intensity in acertain direction to the average radiation intensity in all directions.
If the direction for which the directivity is considered is not specified, weassume the direction in which the antenna has maximum radiation, i.e. weare considering the maximum value of the antenna directivity
Antenna radiation directivity D and the beamsolid angle A are interrelated through thefollowing expression
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Lecture 3. ANTENNA PARAMETERS
Dr Hasanovic: ADVANCED ANTENNA THEORY (Spring 2012
OMNIDIRECTIONAL PATTERN
Figure 3.5. Omnidirectional radiation
pattern
Antenna hasomnidirectional radiation pattern if itsradiation pattern ischaracterized by theuniform radiationintensity in the horizontalplane, i.e. for a constant
value of angle .
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Lecture 3. ANTENNA PARAMETERS
Dr Hasanovic: ADVANCED ANTENNA THEORY (Spring 2012
ANTENNA EFFICIENCYAntenna represents a device that transformsenergy brought on its input terminals into theenergy of an electromagnetic wave radiatedinto the surrounding environment, or opposite.
This transformation of energyis characterized by certainenergy losses.A measure of these losses isgiven through an antennaparameter called antennaefficiency (e).Types of losses:
[1] conductor losses,[2] dielectric losses,[3] mismatch losses
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Lecture 3. ANTENNA PARAMETERS
Dr Hasanovic: ADVANCED ANTENNA THEORY (Spring 2012
ANTENNA EFFICIENCY (cont.)
ANTENNA RADIATION EFFICIENCY(depends on the antenna only and NOT on the feeding line):
Lc coefficient of conductor losses,Ld coefficient of dielectric losses,L coefficient of mismatch losses, voltage reflection coefficient on the antennainput terminals [VSWR= (1+| |/(1 -||)]
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Lecture 3. ANTENNA PARAMETERS
Dr Hasanovic: ADVANCED ANTENNA THEORY (Spring 2012
ANTENNA GAIN Antenna gain (G) is anantenna parameter thattakes into account both itsefficiency and its directionalproperties.
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Lecture 3. ANTENNA PARAMETERS
Dr Hasanovic: ADVANCED ANTENNA THEORY (Spring 2012
POLARIZATION Consider the vector of electricfield E(r,t) and thecorresponding phasor formE(r) where E(r,t)=Re{ E(r)e - jt }then we may notice that theamplitude of this vector forms
a spiral path in time as shownin Figure on the right.
If we fix the point at which we observe thevector of electric field, i.e. E(r=const,t), then this
vector is exclusively a function of the timevariable t.
Antenna polarization is defined as a curve made by the end point of thevector E(r=const,t) in a plane perpendicular to the direction ofelectromagnetic wave propagation.
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Lecture 3. ANTENNA PARAMETERS
Dr Hasanovic: ADVANCED ANTENNA THEORY (Spring 2012
POLARIZATION (demo)
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Lecture 3. ANTENNA PARAMETERS
Dr Hasanovic: ADVANCED ANTENNA THEORY (Spring 2012
POLARIZATION (cont.)
Axial Ratio:
GLAVNA OSA SPOREDNA OSA
Ex(r ,t)
Ey(r ,t)
GLAVNA OSA SPOREDNA OSA
Ex(r ,t)
Ey(r ,t)
MAJOR AXIS MINOR AXIS
Antenna polarization is defined as a curve made bythe end point of the vector E(r=const,t) in a plane
perpendicular to the direction of electromagneticwave propagation.
Three types of polarization:[1] linear (AR=0 or AR=infinity),[2] circular (AR=1)[3] elliptical
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Lecture 3. ANTENNA PARAMETERS
Dr Hasanovic: ADVANCED ANTENNA THEORY (Spring 2012
POLARIZATION (cont.)
E(r =const,t)
E(r =const,t)
E(r =const,t)
E(r =const,t)
E (r =const,t)
E(r =const,t)
VERTIKALNA LINEARNA POLARIZACIJA HORIZONTALNA LINEARNA POLARIZACIJA
DESNA KRU NA POLARIZACIJA LIJEVA KRU NA POLARIZACIJA
DESNA ELIPTI KA POLARIZACIJA LIJEVA ELIPTI KA POLARIZACIJA
E(r =const,t)
E(r =const,t)
E(r =const,t)
E(r =const,t)
E (r =const,t)
E(r =const,t)
VERTIKALNA LINEARNA POLARIZACIJA HORIZONTALNA LINEARNA POLARIZACIJA
DESNA KRU NA POLARIZACIJA LIJEVA KRU NA POLARIZACIJA
DESNA ELIPTI KA POLARIZACIJA LIJEVA ELIPTI KA POLARIZACIJA
VERTICAL LINEAR POLARIZATION
RIGHT CIRCULAR POLARIZATION
RIGHT ELLIPTICAL POLARIZATION
HORIZONTAL LINEAR POLARIZATION
LEFT CIRCULAR POLARIZATION
LEFT ELLIPTICAL POLARIZATION
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Lecture 3. ANTENNA PARAMETERS
Dr Hasanovic: ADVANCED ANTENNA THEORY (Spring 2012
LINEAR POLARIZATION
In practice, it is impossible to achieve ideal linear polarization for which OA or OB isequal to zero.
Let us assume that we have polarization for which OA0.
In this case, the component of electric field in the direction of desired polarization(OB) is called the copolarized component while undesired field component (in thedirection of OA) is called the crosspolarized component. Very often in practice,the goal is to reduce the undesired component (crosspolarized) component. Byreducing the crosspolarized component, the quality of linear polarization isimproved.
E(r =const,t)
E(r =const,t)
VERTIKALNA LINEARNA POLARIZACIJA HORIZONTALNA LINEARNA POLARIZACIJA
E(r =const,t)
E(r =const,t)
VERTIKALNA LINEARNA POLARIZACIJA HORIZONTALNA LINEARNA POLARIZACIJA
VERTICAL LINEAR POLARIZATION HORIZONTAL LINEAR POLARIZATION
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Lecture 3. ANTENNA PARAMETERS
Dr Hasanovic: ADVANCED ANTENNA THEORY (Spring 2012
LINEAR POLARIZATION (demo):
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Lecture 3. ANTENNA PARAMETERS
Dr Hasanovic: ADVANCED ANTENNA THEORY (Spring 2012
CIRCULAR POLARIZATION (demo)
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Lecture 3. ANTENNA PARAMETERS
Dr Hasanovic: ADVANCED ANTENNA THEORY (Spring 2012
INPUT IMPEDANCE OF ANTENNA ANTENAGENERATOR
(Zg)
Xg
Rg
XA
RA
GENERATOR ANTENA
ANTENA
GENERATOR(Zg)
Xg
Rg
XA
RA
GENERATOR ANTENA
Input impedance of an antenna is equal to the ratioof voltage and current on the antenna inputterminals when the antenna is fed from a generator
Real part of antenna input impedance is calledANTENNA INPUT RESISTANCE :
Antenna input resistance represents the measure of power dissipation on theantenna that occurs through two different processes:[1] the portion of the power is being radiated into the surroundingenvironment as an electromagnetic wave[2] the portion of the power is irreversibly lost as a heat in the antennastructure .
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Lecture 3. ANTENNA PARAMETERS
Dr Hasanovic: ADVANCED ANTENNA THEORY (Spring 2012
Generator Impedance:
Impedance Matching:
ggg jXRZ
AgAg XX , RR
2Al
2Arlrul IR2
1IR
21
PPP
ANTENA
GENERATOR(Zg)
Xg
Rg
XA
RA
GENERATOR ANTENA
ANTENA
GENERATOR(Zg)
Xg
Rg
XA
RA
GENERATOR ANTENA
lr
r
RRR
Re
lr
rr RR
Re
INPUT IMPEDANCE OF ANTENNA (cont.) Antenna Input Impedance:
If above conditions are met, then the maximum powerfrom the generator will be delivered to the antenna:
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Lecture 3. ANTENNA PARAMETERS
Dr Hasanovic: ADVANCED ANTENNA THEORY (Spring 2012
ANTENNA FREQUENCY BAND
1. Antenna frequency band is defined as a frequency rangein which antenna meets certain standards relative to aspecified antenna parameter.
2. In other words, for a specified antenna parameter (inputimpedance, beam width, axial ratio, efficiency, etc), acorresponding criterion is defined and then the frequencyband would be the range of frequencies for which that
criterion is satisfied.3. In practice, two frequency band definitions are used onefor the radiation pattern and another for the antennainput impedance .
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Lecture 3. ANTENNA PARAMETERS
D H i ADVANCED ANTENNA THEORY (S i 2012
ANTENNA FREQUENCY BAND (cont.)
1. There exist different definitions of antenna frequency band.2. For broadband antennas , frequency band is usually
defined as the ratio of the highest to the lowest frequency
in the band (for example, 10:1 frequency band means thatthe highest frequency in the band is ten times higher thanthe lowest frequency in the band).
3. For narrowband antennas , frequency band is defined asthe difference between the highest and the lowestfrequency given as a percentage of the center frequency.For example, a frequency band of 5% means that thedifference between the highest and the lowest frequency isequal to 5% of the center frequency.