SMART ANTENNA SYSTEMS Smart Antenna Array antenna array

SMART ANTENNA SYSTEMS

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

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

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

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

A/N SPY-1 phased array radar antenna 6

A/N SPY-1 phased array radar antenna 7

Phased array using slotted elements Flat panel is scanned mechanically 8

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

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

Types of SA Switched lobe (SL) Spatial SDMA Polarization Phased array CDMA Angle Adaptive array

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

Conventional Antennas & Arrays Top View Antenna Array Antenna Omnidirectional Sectorized

WHY SMART ANTENNA ARRAYS ARE SUPERIOR TO CONVENTIONAL ANTENNAS Active Beam Antenna Array Switched Beam System Desired User Interfering User Antenna Array Adaptive Array

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

• 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 (Do. A) tracking algorithm 16

Interference Rejection Comparison Desired Signals Co-channel Interfering Signals

• 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 19

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

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

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 22

Beam Steering Beam direction Equi-phase wave front d 3 = [(2 / )d sin ] 2 0 Radiating elements Phase shifters • Beamsteering using phase shifters at each radiating element Power distribution 23

Dipoles with uniform phase Broadside beam Fig 10. 26 Omni directional dipole array Transmitted RF wave is vertically polarized 24

Phase Dipoles with progressive phase shift 0 o 10 o Beam is depressed to improve coverage of ground 20 o 30 o 40 o Fig 10. 27 Omni directional dipole array Transmitted RF wave is vertically polarized 25

Fig 10. 28 Series Fed Linear Array wavefront Beam direction T wavelets dipoles T T T Equal time delays T load 26

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 27

Cell phone tower with sector and Omni antennas. Small dishes link tower to cell phone HQ and other towers. 28

Cell phone tower with sector antennas 29

Cell phone tower disguised as a tree 30

Fig 10. 32 Parallel Fed Linear Array wavefront Beam direction T wavelets dipoles T T Progressive time delays Splitters 31

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 32

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 0 o • Adjacent element has phase shift • Beam direction is to the array normal where = (2 / ) d sin 33

Fig 10. 33 Setting Beam Angle Beam angle Broadside x d 0 o d x = d sin = (2 / ) d sin 34

Beam Steering • Example #1: Steer beam to 30 o from normal (broadside) • Element spacing d = 0. 6 • = (2 / ) d sin • = 2 x 0. 6 x sin 30 o • = 1. 2 x ½ = 0. 6 = 108 o • We must insert 108 o phase shift between elements 35

Fig 10. 34 Parallel fed linear array scanned 30 o Beam direction 30 degrees 108 o wavefronts 0 108 216 324 Phase Shifts in degrees Splitters 36

Beam Steering • • • Example #2: Steer beam to 45 o from normal Element spacing d = 0. 6 = (2 / ) d sin = 2 x 0. 6 x sin 45 o = 1. 2 x ½ = 0. 848 = 153 o We must insert 153 o phase shift between elements 37

Fig 10. 35 Linear array scanned 45 o Beam direction 45 degrees 153 o wavefronts 0 153 306 99 Phase shifts in degrees Splitters 38

Transmission Part

Reception Part

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

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

SDMA (Space Division Multiple Access)

Comparison of Switched Beam Antenna Adaptive Arrays Criteria Switched Beam Adaptive Array Integration • Easy to implement • Low cost • Transceiver complexity • High cost • Less hardware redundancy Range/ Coverage • More coverage compared to conventional systems to switched beam system • Less coverage compared to adaptive array Interference • Difficulty in distinguishing Rejection between desired signal and interferer • Does not react to the movement of interferers. • Focusing is narrower • Capable of nulling interfering signals

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