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

Antenna Fundamentals Prof. Girish Kumar Electrical Engineering Department, IIT Bombay gkumar@ee.iitb.ac.in (022) 2576 7436

3-D Radiation Pattern of Antenna ` Isotropic Radiation Pattern Omni-Directional Radiation Directional Radiation Pattern Pattern of λ /2 Dipole Antenna D = 1 = 0dB of Microstrip Antenna Array D = 1.64 = 2.1dB D = 500 = 27dB

2-D Radiation Pattern of Antenna ` z Beamwidth between first nulls (FNBW) ~ 2.25 x HPBW Major Lobe (HPBW) (Half Power Beamwidth) (FNBW) Side Lobe Level (SLL) < 20 dB for satellite and high power applications Minor Lobes Side Lobe y Front to Back Ratio (F/B) > 20 dB Back Lobe x

Directivity of Antenna ` 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.  U DU m o 𝐸 = maximum radiation intensity average radiation intensity = 𝑉 max 𝑉 0 𝐸 = 𝑉 max = 4𝜌 𝑉 max = 4𝜌 𝑉 max = 4𝜌 [where , Ω A is beam solid angle P 𝑄 𝑠𝑏𝑒 𝑉 max 𝛻 𝐵 𝛻 𝐵 𝑠𝑏𝑒 U 4𝜌 o 2𝜌 𝜌 1 o (θ, ϕ)| 2 + |E ϕ 𝛻 𝐵 = 𝐺(𝜄, 𝜚)sin𝜄𝑒𝜄𝑒𝜚 o (θ, ϕ)| 2 where, F θ, ϕ ≃ |E θ 𝐺(𝜄, 𝜚)| max 0 0 𝐸 ≃ 4𝜌 [where , θ E , θ H are in radian 𝜄 𝐹 𝜄 𝐼 Example: For Infinitesimal Dipole

Directivity and Gain of Antenna ` Directivity of Large Antenna Directivity of Small Antenna 𝐸 = 32400 41253  where , θ E , θ H are in degree D 𝜄 𝐹 𝜄 𝐼   E H Directivity is proportional to the Effective Aperture Area of Antenna Gain = η D where η is Efficiency of 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 r 2

Polarization of Antenna Orientation of radiated electric field vector in the main beam of the antenna 𝐹 𝜄 𝐹 𝜄 𝐹 𝜄 𝐹 𝜚 𝐹 𝜚 𝐹 𝜚 𝐹 = 𝑏 𝜄 𝐹 𝜄 cos𝜕𝑢 + 𝑏 𝜚 𝐹 𝜚 cos(𝜕𝑢 + 𝛽 𝐷𝑏𝑡𝑓 1: 𝛽 =0 or 𝜌 Wave is Linearly Polarized 𝐷𝑏𝑡𝑓 2 : 𝛽 = ± 𝜌 /2 and E 𝜄 = 𝐹 𝜚 Wave is Circularly Polarized 𝐷𝑏𝑡𝑓 3 : 𝛽 = ± 𝜌 /2 and E 𝜄 ≠ 𝐹 𝜚 Wave is Elliptically Polarized

Axial Ratio of Antenna Axial Ratio(AR) = Major Axis of Polarization Minor Axis of Polarization AR = 1 , circular polarization 1 < AR < ∞ , elliptical polarization AR = ∞ , linear polarization Axial Ratio Bandwidth: Frequency range over which AR < 3 dB Axial Ratio Plot of Circularly Polarized MSA Bandwidth for AR < 3dB = 380MHz (13%)

Input Impedance and VSWR of Antenna Input Impedance Reflection Coefficient and VSWR 𝑎 𝐵 = 𝑆 𝐵 + 𝑘𝑌 𝐵 R A represents power loss  from the antenna and X A Z Z   A 0 gives the power stored in  Z Z A 0   the near field of the R R R A r L antenna   1 V   max VSWR   R R V 1   Radiation Efficiency r r e min  r R R R A r L Practice Problem: Calculate Reflection Coefficient and VSWR for impedance Z A = 10, 30, 50,100 Ω

Input Impedance Plot on Smith Chart Example: If antenna impedance , calculate Γ and VSWR. 𝑎 𝐵 = (20+j30 )𝛻 𝑎 𝐵 = 20𝛻 + 𝑘30𝛻, Z 0 = 50𝛻 𝑎 𝐵 𝑜𝑝𝑠𝑛 = 𝑎 𝐵 = 20 + 𝑘30 = 0.4 + 𝑘0.6 𝑎 0 50 𝛥 = 𝑎 𝐵 − 𝑎 0 𝛥 = 0.56∠112° 𝑎 𝐵 + 𝑎 0 VSWR = 3.55 𝛥 = 20 + 𝑘30 − 50 20 + 𝑘30 + 50 ≃ −0.2 + 0.52j = 0.56∠112° VSWR = 1 + |𝛥| 1 − |𝛥| Normalized Input Impedance Plot on Smith Chart gives Γ and VSWR 1+0.56 VSWR = 1−0.56 ≃ 3.55

Microstrip Antenna at 5.8 GHz ` MSA design at 5.8GHz with RT Duroid 5880 Substrate height =0.8mm Return loss Plot Input Impedance Plot on Smith BW for Γ ≤ 10 dB Chart normalized with 50 ohm is 85MHz (1.5%)

Microstrip Antenna Radiation Pattern and Gain ` Radiation Pattern Antenna Efficiency Plot Antenna Gain Plot HPBW( H-plane) = 88° BW for 1dB Gain Variation = 126MHz HPBW( E-plane) = 80°

Microstrip Antenna Array – Millimeter Wave ` Gain Plot 8x8 EMCP MSA Array at millimeter wave

Radiation Pattern of 8x8 MSA Array ` Main Beam Side Lobe Level Cross Polar Polar Plot Cartesian Plot 32400 𝐺𝑂𝐶𝑋 D = 8.8°x8.8° ≃ 413 = 26.1dB whereas, the simulated directivity is 25.8dB HPBW= 8.8 ° , FNBW=20 ° 𝐼𝑄𝐶𝑋 ≃ 2.27

Link Budget Transmitting antenna Receiving antenna r A et A er Receiver Transmitter 𝑒 = 𝑄 𝑢 𝐻 𝑢 Watt 𝑄 Power Density 𝑛 2 4𝜌𝑠 2 𝑒 𝐵 𝑓𝑠 = 𝑄 𝑢 𝐻 𝑠 𝐵 𝑓𝑠 𝐻 𝑢 = 4𝜌𝐵 𝑓𝑢 𝑄 𝑠 = 𝑄 Watt 4𝜌𝑠 2 𝜇 2 2 𝜇 𝑄 𝑠 = 𝑄 𝑢 𝐻 𝑢 𝐻 𝑠 Watt Friis Transmission Equation 4𝜌𝑠

Power Density 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. P d = P t G t Watt 𝐻 𝑢 = 17𝑒𝐶 = 50 Power density: m 2 4πr 2 P d = 20 x 50 W m 2 4π x 50 2 = 31.8m (a) r = 50m 20 x 50 W m 2 P d = 4π x 300 2 = 0.88m (b) r = 300m

RF Radiation Hazards and Solutions Prof. Girish Kumar IIT Bombay Tel: (022) 2576 7436 gkumar@ee.iitb.ac.in prof.gkumar@gmail.com

Radiation Pattern of a Cell Tower Antenna Primary Lobe Very High High Medium Low Secondary Lobes 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 People living at < 50m are in extremely high radiation zone Power varies by 1/R², where R = Distance from tower

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/m 2 , which is for 6 min period as mentioned in Note no. 3.

EMF Radiation Standards for GSM900 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 *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

Warning from Blackberry Page 18 - Complete manual can be downloaded from - http://docs.blackberry.com/en/smartphone_users/deliverables/11261/BlackBerry_Bold_9700_Smartphone-US.pdf

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

SUGGESTED SOLUTIONS ‘Are cell phones injurious to your health’ by Prof. Girish Kumar Sep. 2011 .

Cell Tower Antenna Radiation 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.

Malignant Brain Tumors vs. Cumulative Use 4000 hours = approx. 1 hour use for 11 years or less than 6 months of 24 hours exposure to 100 mW/m² 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 )