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  2. Smart Antenna Array: • antenna array with a digital signalprocessing capability to transmit and receive in an adaptive and spatiallysensitive manner. • “Smart” >>digital signal processing facility

  3. USAGE • Applications to: • cellular and wireless networks • radar • electronic warfare (EWF) as a countermeasure to electronic jamming • satellite systems

  4. WHY SMART ANTENNA ARRAYS? • Higher Capacity • Higher Coverage • Higher bit rate • Improved link quality • Spectral efficiency • Mobility

  5. Pave Paws phased array antenna Long range VHF radar for detection of ICBMs

  6. A/N SPY-1 phased array radar antenna

  7. A/N SPY-1 phased array radar antenna

  8. Phased array using slotted elements Flat panel is scanned mechanically

  9. Elements of a Smart Antenna number of radiating elements a combining/dividing network control unit

  10. Aim : • to maximize the antenna gain in the desired direction • to minimize the gain in directions of interferers

  11. Switched lobe (SL): ( also called “switched beam” ) simplest technique comprises only a basic switching function between separate directive antennas or predefined beams of an array

  12. Top View Top View Antenna Array Antenna Conventional Antennas & Arrays Omnidirectional Sectorized

  13. Active Beam Desired User Antenna Array Interfering User Antenna Array WHY SMART ANTENNA ARRAYS ARE SUPERIOR TO CONVENTIONALANTENNAS Switched Beam System Adaptive Array

  14. Dynamically phased array (PA): continuous tracking can be achieved by including a direction of arrival (DoA) algorithm for the signal received from the user can be viewed as a generalization of the switched lobe concept

  15. Dynamically phased array (PA): • A generalization of the switched lobe concept • The radiation pattern continuously track the designated signal (user) • Include a direction of arrival (DoA) tracking algorithm

  16. Interference Rejection Comparison Desired Signals Co-channel Interfering Signals

  17. Switched beam antennas • Based on switching function between separate directive antennas or predefined beams of an array • Space Division Multiple Access (SDMA) = allocating an angle direction sector to each user • In a TDMA system, two users will be allocated to the same time slot and the same carrier frequency • They will be differentiated by different direction angles

  18. Polarization Diversity . • For polarization diversity horizontal and vertical polarization is used • Can only double diversity gain • Polarization diversity is known to be effective in urban areas

  19. Angle Diversity • which implements different beam patterns on the different antennas • This combination results in a higher overall gain pattern • Allows the same 120 sectored base station support more users by changing the degree of separation

  20. One Dimensional Phased Array • Simplest phased array is a linear (1-D) array • Elements are in a straight line, spaced d wavelengths apart • Element spacing d must be in range 0.5 to 1.0 wavelengths • Used to create Omni directional antennas with a narrow beam in the vertical plane

  21. Beam-steering using phase shifters at each radiating element  d 3 2  0 Beam Steering Beam direction Equi-phase wave front  = [(2/)d sin] Radiating elements Phase shifters Power distribution

  22. Dipoles with uniform phase Broadside beam Fig 10.26 Omni directional dipole array Transmitted RF wave is vertically polarized

  23. Dipoles with progressive phase shift Phase 0o Beam is depressed to improve coverage of ground 10o 20o 30o 40o Fig 10.27 Omni directional dipole array Transmitted RF wave is vertically polarized 25

  24. Fig 10.28 Series Fed Linear Array wavefront Beam direction wavelets T dipoles T T T T load Equal time delays

  25. Cellular Phone Base Station Antennas • Cell phone base stations use linear array antennas like the one shown in Fig. • The linear array makes a narrow beam in the horizontal plane that is tilted down a little for best coverage over the earth’s surface • Directional elements can be used to make the beam cover a sector • Cell phone towers with a large number of antennas are covering several frequency bands and providing sector coverage to increase the number of users

  26. Cell phone tower with sector and Omni antennas. Small dishes link tower to cell phone HQ and other towers.

  27. Cell phone tower with sector antennas

  28. Cell phone tower disguised as a tree

  29. Fig 10.32 Parallel Fed Linear Array wavefront Beam direction T wavelets dipoles Progressive time delays T T T T Splitters

  30. Beam Steering • Beam is steered by changing relative phase between elements • Fixed time (phase) delays give fixed beam • Cell phone tower antenna has fixed beams • Electronically controlled phase shifter gives movable beam • Used mainly in military radars because of high cost • Elements must be excited with correct amplitude distribution to control sidelobes

  31. Beam Steering • Relative phasing between elements determines beam direction • Analyze for transmit case … apply reciprocity for receive • Consider case of two adjacent elements • One element has phase shift 0o • Adjacent element has phase shift  • Beam direction is  to the array normal where  = (2/) d sin 

  32. Fig 10.33 Setting Beam Angle  Beam angle  Broadside x  d 0o  x = d sin   = (2 / ) d sin  d

  33. Beam Steering • Example #1: Steer beam to 30o from normal (broadside) • Element spacing d = 0.6  •  = (2  / ) d sin  • = 2  x 0.6 x sin 30o • = 1.2  x ½ = 0.6  = 108o • We must insert 108o phase shift between elements

  34. Fig 10.34 Parallel fed linear array scanned 30o Beam direction 30 degrees 108o wavefronts Phase Shifts in degrees 0 108 216 324 Splitters

  35. Beam Steering • Example #2: Steer beam to 45o from normal • Element spacing d = 0.6  •  = (2  / ) d sin  • = 2  x 0.6 x sin 45o • = 1.2  x ½ = 0.848  = 153o • We must insert 153o phase shift between elements

  36. Fig 10.35 Linear array scanned 45o Beam direction 45 degrees 153o wavefronts Phase shifts in degrees 0 153 306 99 Splitters

  37. Transmission Part

  38. Reception Part

  39. Using CDMA with Smart Antenna Technology • In CDMA systems all cells use the same carrier frequency. Users are distinguished by their different codes. • The number of users within one cell is limited mainly by the interference that each user generates for all other users. • By pointing the main beam of the adaptive antenna pattern to the desired user, smart antennas improve the SNIR for one user without increasing interference for the other users. • Note that even an increase of the capacity by only a factor 2 is highly desirable, since it means that twice as many customers can access the network

  40. SDMA (Space Division Multiple Access) more than one user can be allocated to the same physical communications channel simultaneously in the same cell separated by angle only in a TDMA system, two users will be allocated to the same time slot and carrier frequency at the same time and in the same cell

  41. SDMA (Space Division Multiple Access)

  42. Comparison of Switched Beam AntennaAdaptive Arrays

  43. END