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Directional Antenna • Power Level Is Not the Same in All Directions

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Directional Antenna • Power Level Is Not the Same in All Directions Wireless LANs Sep – Dec 2014 Antenna รศ. ดร. อนันต์ ผลเพิ่ม Assoc. Prof. Anan Phonphoem, Ph.D. [email protected] Intelligent Wireless Network Group (IWING Lab) http://iwing.cpe.ku.ac.th Computer Engineering Department Kasetsart University, Bangkok, Thailand 1 Outline • Decibel • Antenna Radiation Pattern • 2.4 GHz Antennas • Cantenna 2 Decibel • A measurement unit • In logarithmic • Relative value (Ratio) • For power / intensity / sound level / voltage • dB • LdB = ratio in decible = Gain P1 LdB = 10 log10( ) P2 3 Example • 2 Loudspeakers P1 P2 • Speaker 1: plays sound with Power P1 • Speaker 2: plays sound with Power P2 •Same environment (frequency, distance) P2 LdB = 10 log10( ) P1 Condition Calculation Decible P2 = P1 10 log10(1) 0 dB P2 = 2 P1 10 log10(2) +3 dB P2 = 0.5 P1 10 log10(0.5) – 3 dB P2 = 10 P1 10 log10(10) +10 dB http://www.phys.unsw.edu.au/jw/dB.html 4 For Electrical Power • Power Gain (GdB) • Calculate 1000 W relative to 1 W G = 10 log ( 1000 W ) = 30 dB 30 dBW dB 10 1 W • Calculate 0.1W relative to 1 mW (milliwatt) G = 10 log ( 100 mW ) = 20 dB 20 dBm dB 10 1 mW 5 Isotropic Antenna • Radiate same power in all directions • In practice, no 100% isotropic antennas • A perfect isotropic antenna, called "isotropic radiator" • Used for measuring the signal strength of real antennas • Contrast with “Anisotropic Antenna” • A directional antenna • Power level is not the same in all directions http://partnerwiki.cisco.com/ViewWiki/ images/2/2b/Omni-vs-direct2-82068.gif 6 Antenna Gain • Ratio of the power density of an antenna’s radiation pattern in the direction of strongest radiation to that of a reference antenna • dBi (DeciBel Isotropic) • The measurement of (forward) gain of a directional antenna • compared with the Hypothetical Isotropic Antenna http://upload.wikimedia.org/wikibooks/en/5/58/Non_isotropic_radiator.gif 7 Example • A directivity of 0 dBi (dB relative to isotropic) • The radiator equally transmits (or receives) electromagnetic radiation to/from any arbitrary direction 8 Antenna Gain • usually represent graphically in polar coordinates • As antenna’s energy conservation • positive gain in some directions • must have negative gain in other directions 9 Antenna Pattern • Also called “Radiation Pattern” • Graphical representation • Describes how the antenna radiates energy out into space (or how it receives energy) • Antenna radiates is actually 3D • Two planar (principle) patterns • Obtained by making two slices through the 3D pattern 10 Antenna Radiation Pattern Antenna Axis Modified from: www.ece.nus.edu.sg/.../Teaching/EE4101/index.htm 11 Radiation Patterns Polar and Cartesian Coordinates 12 Polar Coordinate system • A two-dimensional coordinate system • Each point on a plane is determined by • A distance from a fixed point (pole) • An angle from a fixed direction (polar angle or azimuth) 13 Antenna Measurement Coordinate System The azimuth is the angle formed between a reference direction (North) and a line from the observer to a point of interest projected on the same plane as the reference direction http://en.wikipedia.org/wiki/Azimuth 14 Azimuth (polar angle) Polar Grid Polar http://www.cisco.com/en/US/prod/collateral/wireless/ps7183/ps 469/prod_white_paper0900aecd806a1a3e.html http://en.wikipedia.org/wiki/Polar_coordinate_system 15 2.4 GHz Antennas • Omnidirectional antenna • Dipole Antenna • 5.8 dBi Omnidirectional Antenna • Multiple Element Dipole Antennas • Yagi Antennas • Flat Panel antennas • Parabolic Dish antennas • Slotted Antennas Partial document from: Microstrip Antennas Aerocomm, Lenexa, KS • “Antenna Tutorial” 16 Omni-directional Antenna http://som1.csudh.edu/fac/lpress/471/hout/wireless/antennae.htm 17 Dipole ve3elb.ham-radio.ch/projects.html • Best used for Tx/Rx from broadside • Not a directive antenna Elevation Pattern sin2 (Horizontal Pattern) Works well 360 around antenna Azimuth Pattern Generic Dipole (Vertical Pattern) http://www.engnetbase.com/ 18 Dipole Antenna with 3D Radiation Pattern http://www.cisco.com/en/US/prod/collateral/wireless/ps7183/ps469/prod_white_paper0900aecd806a1a3e.html 19 5.8 dBi Omnidirectional Antenna http://www.cisco.com/en/US/prod/collateral/wireless/ps7183/ps469/prod_white_paper0900aecd806a1a3e.html 20 Directional Antenna http://en.wikipedia.org/ back lobe • Main lobe (beam) • Beamwidth • contains max power • expressed in degrees • greatest field strength • bigger than the others lobes 21 Yagi • Directional Antenna • Not as directional as parabolic dish antenna • An array of independent antenna (director) elements • Only one element driven to transmit electromagnetic waves • The other determines the gain and directivity Elevation Pattern 22 Yagi http://www.cisco.com/en/US/prod/collateral/wireless/ps7183/ps469/prod_white_paper0900aecd806a1a3e.html 23 2.4 GHz 8.8 dBi Yagi Antenna http://directionalantennas.com/yagi_antennas.htm Azimuth Pattern Elevation Pattern • 8.8 dBi directional antenna • 2.4 GHz band • Used in WLAN or WISP applications • Indoors or outside 24 Flat Panel • physically in the shape of a square or rectangle • quite directional http://www.frontierpc.com/ ProductImages/Large/1010892869.jpg Elevation Pattern Azimuth Pattern 25 Single Patch Antenna http://www.cisco.com/en/US/prod/collateral/wireless/ps7183/ps469/prod_white_paper0900aecd806a1a3e.html 26 4x4 Patch Array Antenna http://www.cisco.com/en/US/prod/collateral/wireless/ps7183/ps469/prod_white_paper0900aecd806a1a3e.html 27 4x4 Patch Array Antenna Azimuth Plane Patterns Elevation Plane Patterns http://www.cisco.com/en/US/prod/collateral/wireless/ps7183/ps469/prod_white_paper0900aecd806a1a3e.html 28 Parabolic Dish • Extremely high gain and sharp directivity • Very directional • Use a reflective parabola dish • to focus all received electromagnetic waves on the antenna to a single point http://www.wlan.org.uk/astra%2060cms%20dish.jpg Azimuth Pattern 29 Microstrip http://www.emtalk.com/mwt_mpa.htm • Manufactured with PCB traces on actual PCB boards • Very small and lightweight • Small output power • microstrip antennas are not well suited for wideband communications systems 30 Notebook Antenna (a) Wireless LAN antenna, AUX (black) (b) Wireless WAN antenna, AUX (blue) (c) Camera cable (some models) (d) Wireless WAN antenna, MAIN (red) (e) Wireless LAN antenna, MAIN (gray) (f) MIMO antenna (white) Lenovo: ThinkPad www-307.ibm.com/.../site.wss/MIGR-71582.html 31 WLAN Service Antenna for 2.4GHz "HOT SPOT 16" • 16dBi • Omnidirectional horizontal polarisation www.wlan.org.uk/antenna-page.html 32 Sector antenna (mechanically tilted down by 5 degrees) Coverage Gaps from Elevation Plane Nulls Reduced Coverage Gaps from a Sector Antenna with "Null Fill" 33 Poor Man's WiFi http://askyourpc.com/media/blogs/a/images/wifi_projects.jpg 34 Cantenna • Use a tin can as a waveguide • Use a short wire soldered on an N connector as a probe for coaxial-cable-to waveguide transition • It is a directional antenna • Useful for short to medium distance point- to-point links 35 Cantenna http://www.ipodtouchfans.com/forums/imgcache/26917.png IWING Project http://iwing.cpe.ku.ac.th 36 Building a Cantenna L @2.44 GHz: = 12.2 cm. 0.60 ≤ D ≤ 0.75 7.3 cm. ≤ D ≤ 9.2 cm. L ≥ 0.75 G L ≥ 56.40 cm S = 0.25 G S = 3.05 cm Antenna Gain 10 -14 dBi =wavelength Beam-width 60 degrees G=guide wavelength Summarized from http://www.vias.org/wirelessnetw/wndw_06_08_04.html 37.
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