Antenna Fundamentals Prof. Girish Kumar Electrical Engineering - - PowerPoint PPT Presentation

• Prof. Girish Kumar

Electrical Engineering Department, IIT Bombay

gkumar@ee.iitb.ac.in (022) 2576 7436

Antenna Fundamentals

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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 = 0dB Directional Radiation Pattern

• f Microstrip Antenna Array

D = 500 = 27dB

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2-D Radiation Pattern of Antenna

Back Lobe Minor Lobes (HPBW) (FNBW)

y x

Major Lobe Side Lobe

z

Beamwidth 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

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Directivity of Antenna

• U

m

• U

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.

𝐸 = 𝑉max P

𝑠𝑏𝑒

4𝜌 = 4𝜌 𝑉max 𝑄𝑠𝑏𝑒 = 4𝜌 𝑉max 𝑉max 𝛻𝐵 = 4𝜌 𝛻𝐵 𝐸 ≃ 4𝜌 𝜄𝐹𝜄𝐼 𝐸 = maximum radiation intensity average radiation intensity = 𝑉max 𝑉0 [where, θE, θH are in radian [where, ΩAis beam solid angle 𝛻𝐵 = 1 𝐺(𝜄, 𝜚)|max

2𝜌 𝜌

𝐺(𝜄, 𝜚)sin𝜄𝑒𝜄𝑒𝜚 where, F θ, ϕ ≃ |Eθ

• (θ, ϕ)|2 + |Eϕ
• (θ, ϕ)|2

Example: For Infinitesimal Dipole

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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 degree 𝐸 = 32400 𝜄𝐹𝜄𝐼

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

𝐹 = 𝑏𝜄𝐹𝜄cos𝜕𝑢 + 𝑏𝜚𝐹𝜚cos(𝜕𝑢 + 𝛽

𝐹𝜄 𝐹𝜚 𝐹𝜄 𝐹𝜚 𝐹𝜚 𝐹𝜄

𝐷𝑏𝑡𝑓 3: 𝛽= ± 𝜌/2 and E𝜄≠ 𝐹𝜚 𝐷𝑏𝑡𝑓 2: 𝛽= ± 𝜌/2 and E𝜄= 𝐹𝜚 𝐷𝑏𝑡𝑓 1: 𝛽=0 or 𝜌

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 Impedance

RA represents power loss from the antenna and XA gives the power stored in the near field

• f

the antenna

A r L

R R R  

r r r A r L

R R e R R R   

Radiation Efficiency

A A

Z Z Z Z    

max min

1 V VSWR V 1      

Reflection Coefficient and VSWR

Practice Problem: Calculate Reflection Coefficient and VSWR for impedance ZA= 10, 30, 50,100Ω

𝑎𝐵 = 𝑆𝐵 + 𝑘𝑌𝐵

Example: If antenna impedance , calculate Γ and VSWR.

Input Impedance Plot on Smith Chart

𝑎𝐵= (20+j30)𝛻 𝛥 = 20 + 𝑘30 − 50 20 + 𝑘30 + 50 ≃ −0.2 + 0.52j = 0.56∠112° 𝑎𝐵 = 20𝛻 + 𝑘30𝛻, Z0= 50𝛻 𝛥 = 𝑎𝐵 − 𝑎0 𝑎𝐵 + 𝑎0 VSWR = 1 + |𝛥| 1 − |𝛥| VSWR =

1+0.56 1−0.56 ≃3.55

𝑎𝐵𝑜𝑝𝑠𝑛 = 𝑎𝐵 𝑎0 = 20 + 𝑘30 50 = 0.4 + 𝑘0.6

𝛥 = 0.56∠112°

VSWR = 3.55

Normalized Input Impedance Plot

• n Smith Chart gives Γ and VSWR

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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

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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

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Microstrip Antenna Array – Millimeter Wave

8x8 EMCP MSA Array at millimeter wave Gain Plot

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Radiation Pattern of 8x8 MSA Array

Side Lobe Level Main Beam Cross Polar

Cartesian Plot Polar Plot

HPBW= 8.8°, FNBW=20° 𝐺𝑂𝐶𝑋 𝐼𝑄𝐶𝑋 ≃ 2.27 D = 32400 8.8°x8.8° ≃ 413 = 26.1dB whereas, the simulated directivity is 25.8dB

Link Budget

Receiving antenna Transmitting antenna

r

Transmitter Receiver

Aet Aer

Friis Transmission Equation

Power Density

𝑄

𝑠 = 𝑄 𝑒𝐵𝑓𝑠 = 𝑄 𝑢𝐻𝑠𝐵𝑓𝑠

4𝜌𝑠2 Watt 𝑄

𝑒 = 𝑄 𝑢𝐻𝑢

4𝜌𝑠2 Watt 𝑛2 𝐻𝑢 = 4𝜌𝐵𝑓𝑢 𝜇2

𝑄

𝑠 = 𝑄 𝑢 𝐻𝑢𝐻𝑠

𝜇 4𝜌𝑠

2

Watt

Example: A GSM1800 cell tower antenna is transmitting 20W of power in the

frequency range of 1840 to 1845MHz. The gain of the antenna is 17dB. Find the power density 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 = P

tGt

4πr2 Watt m2 Pd = 20 x 50 4π x 502 = 31.8m W m2 Pd = 20 x 50 4π x 3002 = 0.88m W m2 𝐻𝑢 = 17𝑒𝐶 = 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 0.00001 AUSTRIA (Salzburg city) 1 0.001 BELGIUM 45 to 1125 0.045 to 1.125 BELGIUM (Luxembourg) 24 0.024 BIO-INITIATIVE REPORT (Outdoor) 1 0.001 BIO-INITIATIVE REPORT (Indoor) 0.1 0.0001 CANADA (Toronto Board of Health - proposed) 100 0.1 CHINA 400 0.4 FRANCE (Paris) 100 0.1 GERMANY (ECOLOG 1998 - Precautionary Recommendation) 90 0.09 GERMANY (BUND 2007 - Precautionary Recommendation) 0.1 0.0001 ITALY 100 0.1 NEW ZELAND (Aukland) 500 0.5 POLAND 100 0.1 RUSSIA 100 0.1 SWITZERLAND (Apartments, Schools, Hospitals, Offices & Playgrounds) 42 0.042 USA (Implementation is strict)* 3000 3 (f/300) Final Recommendations Indoor - 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 Kumar
• Sep. 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 years

• r

less than 6 months

• f 24 hours

exposure to 100 mW/m²