ANTENNA ARRAYS

OUTLINES

• What are Arrays?• Radiation Pattern for Arrays• Broadside Array• End-Fire Array• Phased Array• Binomial Array• Benefits• Disadvantages• Applications

WHAT ARE ARRAYS?

• Group of antennas or antenna elements arranged to

provide desired directional characteristics.

• Generally any combination of elements can form an

array.

• However equal elements of regular geometry are

usually used.

•Antenna array is composed of several similar radiating

elements.

Fig.1 Linear array examples

Fig.2 Two-dimensional array of microstrip patch antennas

RADIATION PATTERN FOR ARRAYS

Depends on:

• Type of individual elements

• Their orientation

• Their position in space

• The amplitude and phase of the current feeding

them

• The total number of elements

UNIFORM AMPLITUDE & SPACING

BROADSIDE ARRAY

• Bidirectional Array

• Uses Dipoles fed In-phase and separated by 1/2 wavelength.

• May also be formed from other types of elements, such as horns,

slots, helixes and polyrods.

• Much greater coupling between the antennas than can occur between

collinear elements.

• Changing the distance between the parallel antenna elements

affects the actual impedance of the entire array and the overall

radiation resistance as well.

Beam steering by phase variation is possible.

Fig.3 Broadside array

END-FIRE ARRAY

• Similar to broadside array except dipoles are fed 180 degrees Out of phase.

• Radiation max. at the ends.

• Bidirectional radiation pattern, but with narrower beam widths and lower gain.

• The radiation is in the plane of the driven elements.

• A highly unidirectional antenna can be created by careful selection of the optimal number of elements with the appropriately related spacing.

Radiation is maximum at the ends

Fig.4 End-fire array

PHASED ARRAY

• Relative phases of the respective signals feeding the antennas

are set in such a way that the effective radiation pattern of the

array is obtained in a desired direction and suppressed in

undesired directions.

• Max. radiation in a particular direction.

• So used by warships of many navies in RADAR.

• The shape and direction of pattern is determined by relative

phases & amplitudes of each radiating element.

• Different arrangements possible- linear, planar, conformal

etc.

Radiation pattern obtained in the desired direction

Fig.5 Phased array

UNIFORM SPACING NON-UNIFORM AMPLITUDE

BINOMIAL ARRAY

• Binomial array is an array of non-uniform amplitudes.• Amplitude of the radiating sources are arranged according

to the following binomial series and hence the name

• Coefficients of the expansion represent the relative amplitudes of the elements.

arrayin sources radiating ofnumber m

....... 2!2

)2)(1( )1( 1 1

1

where

xmmxmmx

m=1

m=2

m=3

m=4

m=5

m=6

m=7

The positive coefficients of the series expansion for different values of m are

Fig.6 Binomial array

BENEFITS

• Possibilities to control electronically

– Direction of maximum radiation

– Radiation Pattern

– Directions (positions) of nulls

– Beam-width

– Directivity

– Levels of side lobes

• Reduce secondary lobes

• High Gain

• Cancel out interference from a particular set of directions.

• Determine the direction of arrival of the incoming signals

• Antenna elements can be distributed along straight lines, arcs, squares,

circles, etc.

DISADVANTAGES

• Direct consequence of mutual coupling.

• Can result in complete cancellation of the radiated beam at

some angle.

• Occurs when most of the central elements of the array

have reflection coefficients close to unity.

• Complex & Costly.

APPLICATIONS

• A phased array receiver can be mounted on the top of a commercial airplanes.

• Used for weather forecast.

• Used for tracking missiles and aircrafts such as search radar and tracking radar.

•  Used in systems such as radio broadcasting, broadcast television, two-way radio, communications receivers, cell phones, and satellite communications

• Used in devices such as garage door openers, wireless microphones, Bluetooth-enabled devices, wireless computer networks, baby monitors, and RFID tags on merchandise.

THANK YOU