Antenna Arrays Design and Analysis

1. UNIT-III
ANTENNA ARRAYS
1
Krishna Chaitanya. P Vignan’s University

2. Antenna Arrays
• For some applications single element antennas are
unable to meet the gain or radiation pattern
requirements.
• So, the concept of an antenna array was first introduced
in military applications in the 1940‟s .
• This development was significant in wireless
communications as it improved the reception and
transmission patterns of antennas used in these systems.
• “A Radiating System Consisting of several spaced and properly
phased radiators.”
2
Krishna Chaitanya. P Vignan’s University

3. Antenna Arrays
• The array also enabled the antenna system to be
electronically steered – to receive or transmit
information primarily from a particular direction
without mechanically moving the structure.
• Multiple antenna elements
• Current of different amplitude and phase
• Total pattern is the sum of individual radiation
3
Krishna Chaitanya. P Vignan’s University

4. Advantages of using antenna
arrays
• They can provide a high gain (array gain) by using
simple antenna elements.
• They can provide the capability of a steerable beam,
“steer” the array so that it is most sensitive in a
particular direction
• Cancel out interference from a particular set of
directions
• Determine the direction of arrival of the incoming
signals
4
Krishna Chaitanya. P Vignan’s University

5. Smart array antennas
5
Krishna Chaitanya. P Vignan’s University

6. Smart array antennas
6
Krishna Chaitanya. P Vignan’s University

7. 7
Krishna Chaitanya. P Vignan’s University

8. Antenna Arrays
Array of four axial-mode helical antennas used as a satellite tracking-
acquisition antenna
8
Krishna Chaitanya. P Vignan’s University

9. 6 sector site in CDMA
9
Krishna Chaitanya. P Vignan’s University

10. Types of Array Antenna
• Active and passive array antenna
• Linear array antenna
• Planar array antenna
• Cylindrical array antenna
• Conical array antenna
• Digital array antenna
• Multibeam array antenna
• Multifaced array antenna
• Multifrequency array antenna
• Adaptive array antenna
10
Krishna Chaitanya. P Vignan’s University

11. Linear Array
• Consists of group of identical elements
• Elements placed in 1-D
• Elements placed in specified direction in a straight
line
• Spacing between element may be equal or not
• Used in analysis of directional properties of arrays
11
Krishna Chaitanya. P Vignan’s University

12. Linear Array
• Design of antenna is practical and simpler
• Individual elements may be wire dipoles, loops,
apertures or any other type
• Total field = vector superposition of field radiated by
individual elements
• AFn(normalized) = 1/n[sin(nψ/2) / sin(ψ/2)]
where Afn is the normalized array factor
12
Krishna Chaitanya. P Vignan’s University

13. Linear Array
13
Krishna Chaitanya. P Vignan’s University
planar Array

14. Radiation Pattern for Arrays
Depends on:
• The type of the individual elements
• Their orientation
• Their position in space
• The amplitude and phase of the current feeding
them
• The total number of elements
14
Krishna Chaitanya. P Vignan’s University

15. APPLICATIONS
• A phased array receiver can be mounted on the top
of a commercial airplane's so that all of the happy
passengers can receive satellite television
• It is also used for weather forecast and tracking
missiles and aircrafts; such as search radar and
tracking radar.
15
Krishna Chaitanya. P Vignan’s University

16. Classification of Uniform liner arrays
• Broadside Array
• End fire Array
• Collinear Array
• Parasitic Array
16

17. Broadside Array
• It is an arrangement in which the principal direction of
radiation pattern is perpendicular to the array axis.
• The broadside antenna is bidirectional in radiation.
• The radiation pattern has a very narrow beam width and
high gain.
17
Krishna Chaitanya. P Vignan’s University

18. End Fire Array
• Similar to broadside array except dipoles are fed 180
degrees out of phase
• The end-fire array uses two half-wave dipoles spaced
one-half wavelength apart.
• The end-fire array has a bidirectional radiation
pattern, but with narrower beam widths and lower
gain.
• The radiation is in the plane of the driven elements.
18

19. End Fire Array
• A highly unidirectional antenna can be created by
careful selection of the optimal number of elements
with the appropriately related spacing.
• Higher directivity.
• Generally used for reception.
• End-fire antennas. (a) Bidirectional. (b) Unidirectional
19
Krishna Chaitanya. P Vignan’s University

20. End Fire Array
20
Krishna Chaitanya. P Vignan’s University

21. Collinear array
• All the elements are arranged in coaxial
arrangement, antennas are mounted end to
end in a single line.
• Radiation pattern similar to the BSA.
• Radiation pattern is circular symmetry.
• Optimum spacing is 0.3λ to 0.5λ.
• Collinear array does not use more than four
elements in array.
21
Krishna Chaitanya. P Vignan’s University

22. Collinear array
22
Krishna Chaitanya. P Vignan’s University

23. Parasitic Array
• Feeding is given to one element only.
• It has Driven element and Parasitic element.
Multi element Parasitic Array
23
Krishna Chaitanya. P Vignan’s University