Prof. Girish Kumar - cdeep.iitb.ac.in
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Prof. Girish Kumar Electrical Engineering Department, IIT Bombay [email protected] (022) 2576 7436 Antenna Fundamentals
Transcript of Prof. Girish Kumar - cdeep.iitb.ac.in
Prof. Girish KumarElectrical Engineering Department, IIT Bombay
(022) 2576 7436
Antenna Fundamentals
`3-D Radiation Pattern of Antenna
Omni-Directional Radiation
Pattern of λ/2 Dipole Antenna
D = 1.64 = 2.1dB
Isotropic Radiation Pattern
D = 1 = 0dBDirectional Radiation Pattern
of Microstrip Antenna Array
D = 500 = 27dB
`2-D Radiation Pattern of Antenna
Back Lobe
Minor Lobes
(HPBW)
(FNBW)
y
x
Major Lobe
Side Lobe
zBeamwidth between first nulls
(FNBW) ~ 2.25 x HPBW
(Half Power Beamwidth)
Side Lobe Level (SLL)
< 20 dB for satellite and
high power applications
Front to Back Ratio
(F/B) > 20 dB
`Directivity of Antenna
oU
m oU DU
Directivity of an antenna is the ratio of radiation density in the direction of
maximum radiation to the radiation density averaged over all the directions.
𝐷 =𝑈max
P𝑟𝑎𝑑4𝜋
=4𝜋𝑈max
𝑃𝑟𝑎𝑑=
4𝜋𝑈max
𝑈max 𝛺𝐴=
4𝜋
𝛺𝐴
𝐷 ≃4𝜋
𝜃𝐸𝜃𝐻
𝐷 =maximum radiation intensity
average radiation intensity=
𝑈max
𝑈0
[where, θE, θH are in radian
[where, ΩAis beam solid angle
𝛺𝐴 =1
𝐹(𝜃, 𝜙)|max 0
2𝜋
0
𝜋
𝐹(𝜃, 𝜙)sin𝜃𝑑𝜃𝑑𝜙 where, F θ, ϕ ≃ |Eθo(θ, ϕ)|2 + |Eϕ
o (θ, ϕ)|2
Example: For Infinitesimal Dipole
`Directivity and Gain of Antenna
Gain = η D
Directivity of Large Antenna
Practice Problem: Find the gain in dB of a parabolic reflector antenna at 15 GHz
having diameter of 1m. Assume efficiency is 0.6. What will be its gain at 36 GHz?
Hint: Aperture Area of parabolic reflector antenna = π r2
where, θE, θH are in degree𝐷 =32400
𝜃𝐸𝜃𝐻
where η is Efficiency of Antenna
Directivity is proportional to the Effective Aperture Area of Antenna
41253
E H
D
Directivity of Small Antenna
Polarization of Antenna
Orientation of radiated electric field vector in the main beam of the antenna
Wave is Linearly Polarized
Wave is Circularly Polarized
Wave is Elliptically Polarized
𝐸 = 𝑎𝜃𝐸𝜃cos𝜔𝑡 + 𝑎𝜙𝐸𝜙cos(𝜔𝑡 + 𝛼
𝐸𝜃
𝐸𝜙
𝐸𝜃
𝐸𝜙 𝐸𝜙
𝐸𝜃
𝐶𝑎𝑠𝑒 3: 𝛼= ± 𝜋/2 and E𝜃≠ 𝐸𝜙
𝐶𝑎𝑠𝑒 2: 𝛼= ± 𝜋/2 and E𝜃= 𝐸𝜙
𝐶𝑎𝑠𝑒 1: 𝛼=0 or 𝜋
Axial Ratio of Antenna
Axial Ratio Bandwidth: Frequency range over which AR < 3 dB Axial Ratio Plot of Circularly Polarized MSA
Bandwidth for AR < 3dB = 380MHz (13%)
, circular polarization
, elliptical polarization
, linear polarization
AR = 1
1<AR<∞
AR = ∞
Axial Ratio(AR) =Major Axis of Polarization
Minor Axis of Polarization
Input Impedance and VSWR of Antenna
Input ImpedanceRA represents power loss
from the antenna and XA
gives the power stored in
the near field of the
antennaA r LR R R
r r
r
A r L
R Re
R R R
Radiation Efficiency
0
0
A
A
Z Z
Z Z
max
min
1VVSWR
V 1
Reflection Coefficient and VSWR
Practice Problem: Calculate Reflection Coefficient and VSWR for impedance ZA = 10, 30, 50,100Ω
𝑍𝐴 = 𝑅𝐴 + 𝑗𝑋𝐴
Example: If antenna impedance , calculate Γ and VSWR.
Input Impedance Plot on Smith Chart
𝑍𝐴= (20+j30)𝛺
𝛤 =20 + 𝑗30 − 50
20 + 𝑗30 + 50≃ −0.2 + 0.52j = 0.56∠112°
𝑍𝐴 = 20𝛺 + 𝑗30𝛺, Z0= 50𝛺
𝛤 =𝑍𝐴 − 𝑍0
𝑍𝐴 + 𝑍0
VSWR =1 + |𝛤|
1 − |𝛤|
VSWR =1+0.56
1−0.56≃3.55
𝑍𝐴𝑛𝑜𝑟𝑚=
𝑍𝐴
𝑍0=
20 + 𝑗30
50= 0.4 + 𝑗0.6
𝛤 = 0.56∠112°
VSWR = 3.55
Normalized Input Impedance Plot
on Smith Chart gives Γ and VSWR
`Microstrip Antenna at 5.8 GHz
Return loss Plot
BW for Γ ≤ 10 dB
is 85MHz (1.5%)
Input Impedance Plot on Smith
Chart normalized with 50 ohm
MSA design at 5.8GHz
with RT Duroid 5880
Substrate height =0.8mm
`Microstrip Antenna Radiation Pattern and Gain
Antenna Gain Plot
BW for 1dB Gain Variation = 126MHz
Radiation Pattern
HPBW( H-plane) = 88°
HPBW( E-plane) = 80°
Antenna Efficiency Plot
`Microstrip Antenna Array – Millimeter Wave
8x8 EMCP MSA Array at millimeter wave Gain Plot
`Radiation Pattern of 8x8 MSA Array
Side Lobe
Level
Main Beam
Cross
Polar
Cartesian PlotPolar Plot
HPBW= 8.8°, FNBW=20°𝐹𝑁𝐵𝑊
𝐻𝑃𝐵𝑊≃ 2.27 D =
32400
8.8°x8.8°≃ 413 = 26.1dB whereas, the simulated directivity is 25.8dB
Link Budget
Receiving antennaTransmitting antenna
r
Transmitter Receiver
Aet Aer
Friis Transmission Equation
Power Density
𝑃𝑟 = 𝑃𝑑𝐴𝑒𝑟 =𝑃𝑡𝐺𝑟𝐴𝑒𝑟
4𝜋𝑟2Watt
𝑃𝑑 =𝑃𝑡𝐺𝑡
4𝜋𝑟2 Watt𝑚2
𝐺𝑡 =4𝜋𝐴𝑒𝑡
𝜆2
𝑃𝑟 = 𝑃𝑡 𝐺𝑡𝐺𝑟
𝜆
4𝜋𝑟
2
Watt
Example: A GSM1800 cell tower antenna is transmitting 20W of power in thefrequency range of 1840 to 1845MHz. The gain of the antenna is 17dB. Find the powerdensity at a distance of (a) 50m and (b) 300m in the direction of maximum radiation.
Power density:
(a) r = 50m
(b) r = 300m
Power Density
Pd =PtGt
4πr2 Wattm2
Pd =20 x 50
4π x 502= 31.8m W m2
Pd =20 x 50
4π x 3002= 0.88m W m2
𝐺𝑡 = 17𝑑𝐵 = 50
RF Radiation Hazards and
Solutions
Prof. Girish Kumar
IIT Bombay
Tel: (022) 2576 7436
People living within 50 to 300 meter radius are in the high radiation
zone (dark blue) and are more prone to ill-effects of electromagnetic
radiation
Radiation Pattern of a Cell Tower Antenna
People living at < 50m are in extremely high radiation zone
Power varies by 1/R², where R = Distance from tower
Primary Lobe
Secondary Lobes
Very High High Medium Low
ICNIRP Guidelines – Adopted by India till Aug. 31, 2012
According to ICNIRP, for general public exposure, safe power density = f/200 for frequency range of 400-2,000 MHz. So for GSM900, safe power density is 900/200 = 4.5W/m2, which is for 6 min period as mentioned in Note no. 3.
Country Milliwatt / m² Watt / m² INDIA (adopted ICNIRP) 4500 4.5 (f/200) INDIA (Adopted 1/10th of ICNIRP on Sep. 1, 2012) 450 0.45 (f/2000) AUSTRALIA (New South Wales proposed) 0.01 0.00001AUSTRIA (Salzburg city) 1 0.001BELGIUM 45 to 1125 0.045 to 1.125 BELGIUM (Luxembourg) 24 0.024BIO-INITIATIVE REPORT (Outdoor) 1 0.001BIO-INITIATIVE REPORT (Indoor) 0.1 0.0001CANADA (Toronto Board of Health - proposed) 100 0.1CHINA 400 0.4FRANCE (Paris) 100 0.1GERMANY (ECOLOG 1998 - Precautionary Recommendation) 90 0.09GERMANY (BUND 2007 - Precautionary Recommendation) 0.1 0.0001ITALY 100 0.1NEW ZELAND (Aukland) 500 0.5POLAND 100 0.1RUSSIA 100 0.1SWITZERLAND (Apartments, Schools, Hospitals, Offices & Playgrounds) 42 0.042USA (Implementation is strict)* 3000 3 (f/300)Final RecommendationsIndoor - include apartments, schools, hospitals, offices & playgrounds. 0.1 0.0001 Outdoor - where people spend few minutes a day. 10 0.01
EMF Radiation Standards for GSM900
*USA - FCC Guidelines OET56: Power transmitted is 0.5 to 1 W in the Urban Area
Guidelines of the Austrian Medical Association
Adopted on 3rd March 2012 in Vienna
Page 18 - Complete manual can be downloaded from -http://docs.blackberry.com/en/smartphone_users/deliverables/11261/BlackBerry_Bold_9700_Smartphone-US.pdf
Warning from Blackberry
WHO: Cell Phones can Increase Cancer Risk
International Agency for Research on Cancer (IARC), a part of WHO designates cell phones as “Possible Human Carcinogen” [Class 2B]
Found evidence of increase in glioma and acoustic neuroma brain cancer for mobile phone
‘Are cell phones injurious to your health’ by Prof. Girish KumarSep. 2011.
SUGGESTED SOLUTIONS
Antennas on Cell tower transmit in the frequency range of:• 869 - 890 MHz (CDMA)• 935 - 960 MHz (GSM900) • 1805 – 1880 MHz (GSM1800)• 2110 – 2170 MHz (3G)• 2300 – 2400 MHz (4G)*• 2400 – 2500 MHz (Wi-Fi, Bluetooth)http://www.wifiinschools.com/This website is dedicated to help the public realize that wireless internet, or WiFi, emits radiation that causes a myriad of serious health effects, including damage to DNA, cancer, and infertility.
Cell Tower Antenna Radiation
Malignant Brain Tumors vs. Cumulative Use
L. Hardell, M. Carlberg, Mobile phone and cordless phone use and the risk for glioma – Analysis of pooled case-control studies in Sweden, 1997–2003 and 2007–2009, Pathophysiology (Oct. 2014)
4000 hours = approx. 1 hour use for 11 yearsor
less than
6 months
of 24 hours
exposure to 100
mW/m²
