Prof. Girish KumarElectrical Engineering Department, IIT Bombay

gkumar@ee.iitb.ac.in

(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

gkumar@ee.iitb.ac.in

prof.gkumar@gmail.com

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