Antenna array

FDP on Antennas –Savitha Engg. College
24 June 2020
Department of
Electronics & Communication
Engineering
Since 1987
Concepts of Antenna Array
and its applications
Dr.A.Amsaveni
Professor
Department of ECE
Kumaraguru College of Technology
Coimbatore, Tamilnadu
Email id: amsaveni.a.ece@kct.ac.in

24 June 2020 2

24 June 2020
• Historical Perspective:
Jill Tarter (1944) is an American astronomer who uses arrays of radio antennas
to search for extraterrestrial life. She is the former director of the Center for
SETI Research and was the inspiration for the main character in the movie
Contact.

24 June 2020
Presentation Outline
 Antenna Array
 Need for Antenna Array
 Types of Antenna Array
 Antenna Array parameters
 Pattern multiplication
 Applications of Antenna Array
 Smart Antennas

24 June 2020
Antenna
 An antenna is a passive structure that serves as a transducer between transmission
line and air in order to receive and transmit electromagnetic waves.
 An Antenna is an electrical device which converts electric energy into radio waves,
and vice versa. It is usually used with a radio transmitter or radio receiver.
 An antenna is a device used for sending or receiving Electromagnetic waves.

24 June 2020
Antenna Array
 An antenna array is group of antennas connected and arranged in a regular
structure to form a single antenna that is able to produce radiation patterns not
produced by individual antennas.
 Antenna arrays are groups of isotropic radiators which radiate or receive
electromagnetic energy.
 They provide a solution to the problems caused by single antennas.
 Antenna array composed of several similar radiating elements (e.g., dipoles or
horns).
 Element spacing and the relative amplitudes and phases of the element
excitation determine the array’s radiative properties.

24 June 2020
 Generally any combination of elements can form an array.
 However equal elements of regular geometry are usually used.
 Antenna array is used to modify the radiation pattern. Generally it is
used to increase the directivity of the antenna.
 Usually, arrays have many applications. But, these are most often used
to improve the gain and shape the radiation pattern of an antenna
system effectively

24 June 2020
Examples of Antenna array

24 June 2020
Owens Valley Radio
Observatory

24 June 2020
The New Mexico Very Large Array
27 antennas along 3 railroad tracks provide baselines up to 35 km. Radio
images are formed by correlating the signals collected by each antenna.

24 June 2020
Need for Antenna Array
• Single element
 Provides Wide beam and low directivity
 To have very high gain and long distance antenna, Increase the electrical
size of the antenna .But Increasing size -> difficult to build and expensive
 Useful especially when the element gain is low.
• Advantages of Antenna Array over single element
 Higher directivity
 Narrower beam
 Lower side lobes
 Electronic steerable beam
 The total field is determined by the vector addition of the fields radiated
by the individual elements

24 June 2020
In general antenna array can be used to :
 increase the overall gain
 provide diversity reception
 cancel out interference from a particular set of directions
 "steer" the array so that it is most sensitive in a particular
direction
 determine the direction of arrival of the incoming signals
 maximize the Signal to Interference Plus Noise Ratio (SINR)

24 June 2020
• Controlling Parameters that can be used to shape the overall
pattern of the antenna
 Geometrical configuration (linear, circular, etc.)
 Relative spacing between elements
 Excitation amplitude of individual elements
 Excitation phase of individual elements
 Relative pattern of individual elements
 Frequency of operation( wavelength), f = c/λ

24 June 2020 14

24 June 2020
TYPES Of ANTENNA ARRAY
1.Linear Antenna Array
 Broad side array.
 End fire array.
 Parasitic array.
 Driven array.
2.Circular Antenna Array
3.Planar Array
4.Phased Array

24 June 2020
• Linear Array
• An antenna array is said to be linear, if the individual antennas of the
array are equally spaced along a straight line.
• Uniform Linear Array
• A uniform linear array is one in which the elements are fed with a
current of equal magnitude with uniform phase shift along the line.

24 June 2020
Broadside array
 The broadside array is one in which a number of identical parallel antennas are set up
along a line drawn perpendicular to their respective axes.
 In the broadside array, the individual antennas are equally spaced along a line and
each element is fed with current of equal magnitude, all in the same phase.
 By doing so, this arrangement radiates in broadside directions (i.e.,perpendicular to
the line of array axis) where there are maximum radiation and relatively a little
radiation in other directions.
 Radiation pattern of broadside array is bidirectional (radiates equally well in
either direction of maximum radiation).

24 June 2020
• The bidirectional pattern of broadside array can be converted into
unidirectional by installing an identical array behind this array at a
distance /4 and exciting it by a current leading in phase by 90° or /2
radians.

24 June 2020
End-fire array
 The end fire array is nothing but broadside array except that individual elements
are fed in, out of phase (usually 180º).
 End fire array is one in which a number of identical elements are fed with currents
of equal magnitude but their phases varies progressively along the line in such a way
that it provides unidirectional pattern.
 End fire array may be defined as the arrangement in which the principal direction of
radiation coincides with the direction of array.
 The radiation pattern of end fire array is unidirectional
 The end fire array may be bidirectional. Example, two elements array, fed with equal
current, 180º out of phase.

24 June 2020
Parasitic Array Antenna (yagi-uda antenna)
used for controlling radar and various other narrow beams such as the microwave
communication system.
Driven Array Antenna (Log –periodic antenna)
Radiating elements are connected to an energy source and have less loss
when compared to parasitic arrays, but still maintain the narrow beam
characteristics, are used as search radar antennas where narrow beams are
less critical when compared to low losses.

24 June 2020
Circular Array
 Antenna elements arranged around a circular ring.
 Unlike linear arrays, circular arrays can provide a 2D angular scan, both
horizontal φ and vertical θ scans.
 Unlike 2D planar arrays, circular arrays are basically 1D linear arrays but
in a circular form.
 Unlike linear arrays, a circular array can scan horizontally for 360° with no
distortions near the endfire directions.
 Applications are radio direction finding, air and space navigation,
underground propagation, radar, sonar.
Circular Microstrip Array

24 June 2020

24 June 2020
Binomial Array
• To reduce the sidelobe level, John Stone proposed that sources have amplitudes
proportional to the coefficients of a binomial series of the form,
• where n is the number of sources. Thus for arrays of 2 to 6 sources, the relative
amplitudes are given by,

24 June 2020
These coefficients for any number of radiating sources can also be obtained
from Pascal’s triangle.
In Pascal’s triangle, each internal integer (leaving the side integer) is the sum
of the above adjacent integers.
However, the elimination of secondary lobes takes place at the cost of directivity.

24 June 2020
• But the half power beam width (HPBW) of binomial array is more than that of
uniform array for the same length of array. Example: for n = 5, spaced /2
apart, HPBW of binomial array is 31° with no side lobes, But HPBW of uniform
array is 23°.
• Thus, in uniform array secondary lobes appear but principle lobe is sharp and
narrow where as in Stone’s binomial array, width of beam widens but without
secondary lobes.
• Disadvantages
• 1. HPBW increases and hence the directivity decreases.
• 2. For design of a large array, larger amplitude ratio of sources is required.

24 June 2020
Array Antenna Characteristics
Gain
• An antenna array can achieve higher gain (directivity), that is a narrower
beam of radio waves, than could be achieved by a single element. In a
broadside array, the array gain is almost exactly proportional to the length of
the array.
Radiation pattern
• The radiation pattern of such an antenna consists of a strong beam in one
direction, the main lobe, plus a series of weaker beams at different angles
called sidelobes, usually representing residual radiation in unwanted
directions.
Directivity
• Directivity is also defined for an antenna receiving electromagnetic waves its
directivity when receiving is equal to its directivity of transmitting. The
directivity of an actual antenna can vary from 1.76 dBi for a short dipole, to as
much as 50 dBi for a large

24 June 2020
Beam-width
• The beam width is the product of the individual antenna pattern and the
"array factor" shape.
Bandwidth
• It is is affected by many factors, Including impedances with frequency,
change of array spacing in wavelengths that may allow grating lobes,
change in element beam width, and so on…
• When an array is scanned with fixed units of phase shift, provided by
phasers, there is also a band width limitation as the position of the main
beam will change with frequency.

24 June 2020
Directivity
• In an antenna array, the directivity of the entire array is the multiplicative
sum of the individual antenna's directivity function with a mathematical
expression known as the array factor which typically depends on the location,
the excitation and the phase of each antenna element.
• The overall directivity function is given by,
Darray(β,Φ)=AF * D(β,Φ)
Where D(β,Φ) is the directivity of a single element. This single element term is
sometimes referred to as the element pattern.

24 June 2020
Phased Arrays
 Array of N antennas in a linear or two-dimensional configuration + beam-forming
& control device
 The amplitude and phase excitation of each individual antenna controlled
electronically (“software-defined”)
 Phased array usually means an electronically scanned array, a computer-
controlled array of antennas which creates a beam of radio waves that can be
electronically steered to point in different directions without moving the
antennas.
 In phased array, the power from the transmitter is fed to the antennas through
devices called phase shifter.
 High gain low sidelobes
 Multi-target handling multifunction by radiating several beam
 More reliable

24 June 2020
 Consist of multiple (usually identical) antennas (elements) ‘collaborating’ to
synthesize radiation characteristics not available with a single antenna.
 They are able to match the radiation pattern to the desired coverage area
 to change the radiation pattern electronically (electronic scanning) through the
control of the phase and the amplitude of the signal fed to each element
 to adapt to changing signal conditions
 to increase transmission capacity by better use of the radio resources and
reducing interference
 Complex & costly
 Intensive research related to military, space, etc. activities

24 June 2020
 Phased array antennas are an antenna that has multiple radiating elements
each connecting to a phase shifter. The phase shifting allows the radiation
pattern to be “steered” towards a certain direction.
 The lobe is increased upward as a result of the phase shift demonstrating by
changing the phase one can steer the beam in desired location without actually
moving the element.
 A phased array antenna is an array antenna whose single radiators can be fed with
different phase shifts.
 As a result, the common antenna pattern can be steered electronically.
 The electronic steering is much more flexible and requires less maintenance than
the mechanical steering of the antenna.
 Enabled - electronically steered – to receive or transmit info from a particular
direction without mechanically moving the structure.
 Appln: Used in Radars as it requires antennas with steering capabilities.

24 June 2020
• Advantages and Disadvantages of Phased Arrays
• Advantages:
 high antenna gain with large side-lobe attenuation
 very fast change of beam direction (in range of microseconds)
 high beam agility
 arbitrary space scanning
 multi-function operation by simultaneous generation of multiple beams
 failure of some components does not result in a complete system failure.
• Disadvantages:
 limited scanning range (up to max. 120° in azimuth and elevation)
 Deformation of the antenna pattern during beam steering
 low frequency agility
 very complex structure (computer, phase shifter, data bus to each radiator)
 high cost

24 June 2020
Possible Arrangements of Phased Array
• Linear Array
• These phased array antennas consist of lines, which are commonly
controlled by a single phase shifter. (Only one phase shifter is needed
per group of radiators in this line.) A number of linear arrays arranged
vertically on top of each other form a flat antenna.
• Advantage: simple arrangement;
• Disadvantage: beam steering only in a single plane;
• Planar Array
• These phased array antennas consist completely of single elements
with a phase shifter per element. The elements are arranged like a
matrix, the flat arrangement of all elements forms the entire antenna.
• Advantage: beam deflection possible in two planes
• Disadvantage: a large number of phase shifters

24 June 2020
• Frequency Scanning Array
• The frequency scanning array is a special case of the phased array antenna,
in which the beam steering is controlled by the transmitter's frequency
without use of any phase shifter. The beam steering is a simple function of
the frequency. This type of phased array antenna was often used in older
radar sets.

24 June 2020
• Types of phased array
 Passive phased array(PESA)
 Active electronically scanned array(AESA)
 Hybrid beam forming phased array
 Digital beam forming(DBF) array
• Disadvantages
 Complex structure
 High cost
 Low frequency bandwidth
44

24 June 2020 45

24 June 2020
Planar Array
 An antenna in which all of the elements, both active and parasitic, are in one plane.
 A planar array provides a large aperture and may be used for directional beam
control by varying the relative phase of each element.
 Antenna elements arranged over some planar surface (example - rectangular array).
 Planar arrays are more versatile;
 They provide more symmetrical patterns with lower side lobes, much higher
directivity (narrow main beam).
 They can be used to scan the main beam toward any point in space.
 much higher directivity (narrow main beam).
 Applications – tracking radars, remote sensing, communications, etc.

24 June 2020
Smart antenna systems

24 June 2020
Why Smart antennas?
 Increases the number of subscribers(Higher system capacity)
 Higher data transmission rate
 Better spectral efficiency
 Extended range
 Processing of multipath propagating signal
TYPES:
 Switched beam- a finite number of fixed, predefined patterns or
combining sectors
 Adaptive array - an infinite number of patterns (scenario-based ) that
are adjusting in real time.
48

24 June 2020
 Smart antenna is not smart, it is the digital signal processing doing
with antenna which makes the system smart.
 It is the antenna phased array with DSP processor
 High gain for desired direction
 Interference Rejection
 Increases the system capacity
49

24 June 2020
Adaptive (“Intelligent”)Antennas
 Array of N antennas in a linear, circular, or planar configuration
 Used for selection signals from desired sources and suppress incident
signals from undesired sources.
 The antenna pattern track the sources.
 It is then adjusted to null out the interferers and to maximize the signal
to interference ratio (SIR).
 Able to receive and combine constructively multipath signals.

24 June 2020
Adaptive antenna array
A set of 48 2GHz antennas
• An adaptive antenna is an antenna of which the
antenna radiation (or reception) pattern can be
adjusted dynamically.
• An adaptive antenna consists of a number of
antennas(called as elements).
• Adaptive antennas use signal processing algorithms
to combine the signals from the different elements
in such a way that the desired signal is received (or
sent in a particular direction) or that interfering
signals or multipath signals are optimally
suppressed.

24 June 2020
Switched beam array
 Switched beam systems have several available fixed beam patterns.
 A decision is made as to which beam to access, at any given point in time,
based upon the requirements of the system.
 Overall goal of switched beam system to increases gain according to the
location of the user
•

24 June 2020
ANTENNA ARRAY APLICATIONS
• An array widely used as a base-station antenna for mobile
communication.
• Yagi-Uda array is used to TV and radio application
• Log periodic antenna is used for TV with wider bandwidth
• Broadcasting
• Beam forming
• Naval usage
• optical phased arrays
• Radio-frequency identification (RFID)
• Weather research usage
• Missiles guidance
• Fire radar aircraft…etc.. Are the areas in which array antennas are used

24 June 2020
Application of Antenna Arrays to
Mobile Communications
• Array processing is expected to play an important role in fulfilling the
increased demands of various mobile communications services
• Array processing involves manipulation of signals induced on various
antenna elements. Its capabilities of steering nulls to reduce co-channel
interferences and pointing independent beams toward various mobiles
• It has the ability to provide estimates of directions of radiating sources,
make it attractive to a mobile communications system designer

24 June 2020 55

Antenna array

More Related Content

What's hot

Similar to Antenna array

Recently uploaded

Antenna array