Array antennas

Broadside, End Fire & binomial array antennas

bySushant Burde (B-48)

Vaibhav Deshmukh(B-52)Rohit Dhongde(B-41)

Pratik Suryavanshi(B-40)

Driven Arrays: Broadside Antenna

A broadside array is a stacked collinear antenna consisting of half-wave dipoles spaced from one another by one-half wavelengths.

This antenna produces a highly directional radiation pattern that is broadside or perpendicular to the plane of the array.

The broadside antenna is bidirectional in radiation, but the radiation pattern has a very narrow beam width and high gain.

Broadside ArrayBidirectional Array

Uses Dipoles fed in phase and separated by 1/2 wavelength

Broadside arrays may also b e formed from other types of elements, such as horns, slots, helixes and polyrods

O. Kilic EE 542 4

Radiation Pattern for ArraysDepends 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

Broadside ArraysBeam steering by phase variation is possible.

broadside array antenna

Figure 14-30: A broadside array.

Driven Arrays: End-Fire Antenna

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.

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

End-Fire ArraySimilar to broadside array except dipoles are fed

180 degrees out of phase

Radiation max. off the ends

End-fire Arrays Higher directivity.

Provide increased directivity in elevation and azimuth planes.

Generally used for reception.

Impedance match difficulty in high power transmissions.

Variants are:Horizontal Array of DipolesRCA Fishborne AntennaSeries Phase Array

End fire arrays

F: End-fire antennas. (a) Bidirectional. (b) Unidirectional.

Binomial array antennaBinomial array is an array of non-uniform

amplitudes and the amplitude of the radiating sources are arranged according to the co-efficient of successive term of the following binomial series and hence the name

Advantages To reduce secondary lobes

2. to optimize them.

As we increase the array length the directivity increases and side lobes appear.

Pattern multiplicationMultiplication pattern is the total field pattern of

an array of non-isotropic but similar source

It is the multiplication of the individual source pattern and the pattern of an array of isotropic point source each located at the phase centre of individual sources having the relative amplitude and phase T

The total phase pattern is the addition of the phase pattern of ‘the individual source and that of the array of isotropic point sources.

Principle

The total field pattern of an array of non-isotropic but similar sources is the product of the individual source &The array pattern of isotropic point sources each located at the phase centre of the individual source and the array pattern of isotropic point sources each located at the phase centre of the individual sources having the same amplitude and phase.