Antenna Array : Design, Working, Types & Its Applications

An antenna is a specialized device that can radiate some amount of energy within a particular direction for better output transmission. For more efficient output, a few more antenna elements are added to it which are known as Antenna arrays. A single antenna has good directivity but somewhat fails in signal transmission to the receiver with losses so an antenna array is used. So in so many applications, we need antennas with extremely high directive characteristics which can be enhanced by increasing the antenna’s electrical size. To increase the antenna’s dimension without increasing the size of the individual elements is to form antenna array elements. This article discusses an overview of antenna array – types and their working with applications.

What is an Antenna Array?

An antenna array definition is; a group of antennas that are arranged to form a single antenna to generate radiation patterns but not generated by individual antennas. So a set of antennas will work together to transmit or receive radio signals. The designing and maintaining of this antenna are cost-effective as every antenna is smaller. The antenna array diagram is shown below.

For the antenna array, proper spacing & phase must be given while configuring. Once antennas transmit a signal to a very long distance then it required that they have to possess high directive gain as the signal deforms and distorts while transmitting from one end to other. Although, a single antenna transmits with a  good directivity, it fails to transmit a signal from transmitter to receiver without losses. So this is the main reason to use the antenna array.

Array Antenna Design

An antenna array is designed by arranging several antennas to make a single system to provide high directive gain. Antennas within the array must be spaced properly & in the proper phase so that the independent contribution of every antenna within the arrangement in the same direction gets added up whereas it gets canceled out in rest all other directions. This kind of arrangement improves the system’s directivity. Once all the antennas within a system are arranged in a straight line it is known as a linear antenna array.

Antenna Array Working

An antenna array is a set of various antenna elements. In general, a multi-element array utilizes a half-wave dipole antenna. This antenna has an omnidirectional radiation pattern so the waves are emitted above a wide angle. To enhance these antennas’ ability to emit especially in a single direction, these antennas are simply arranged in the array form with proper spacing. These arrays are simultaneously excited by providing current by proper phase.

Generally in an array of antennae, the currents within the different antenna elements are in phase if it achieves the highest value on flowing throughout a similar direction at the same time. Thus, once the antenna elements are fed with the proper phase from every element of the array, the spherical waves are superimposed because of interference & generate a radio wave. Here in the system, the interference can be either constructive (or) destructive and completely depends on the radiated waves by the elements.

As a result, if the emitted waves from the antenna elements are in phase, they are added usefully, so that it increases the radiated power. Whereas, if the waves emitted from the individual elements are not in phase, then they are added destructively to cancel out each other. So this can cause a reduction in the radiated power.

Like this, the emitted radiations from the array elements are in phase and add up to provide a directional beam that has maximum strength so that it can travel very long distances. Thus, the radiation pattern provided by an antenna array has a main lobe that specifies a strong beam in a single direction. When the number of elements in the array is increased, the main lobe gets narrower & smaller side lobes specify an increase in the gain provided by the antenna.

Array Antenna Types

Array antennas are classified into four types broadside, end-fire, collinear & parasitic antenna array where each type is discussed below.

Broadside Antenna Array

The broadside antenna array arrangement is shown below where various identical elements are parallelly arranged along the antenna axe line. In this type of arrangement, the elements are arranged horizontally arranged at an equivalent distance to each other & every element is fed by a current of similar phase & magnitude.

Whenever the elements in this arrangement are energized then maximum radiation will be emitted from the broadside which means the normal direction to the array axis whereas some amount of radiation will be emitted from the other directions. So it provides a bidirectional radiation pattern because it radiates within both directions along the broadside. Therefore, in this arrangement, the direction of radiation principle is common to the array axis & the plane of element position. The radiation pattern of the broadside antenna array is shown below.

The radiation pattern of the broadside antenna array is vertical because the element’s alignment is horizontal.

If we want to change the radiation pattern from bidirectional to unidirectional then a similar array needs to arrange at λ/4 distance behind this antenna array & exciting the replica array through a current having a 90° phase lead. Usually, the number of elements within this arrangement depends on available space with the need of cost & beam width whereas the array length is taken in between 2 λ to 10 λ. Generally, these antenna arrays are used in overseas broadcasting systems.

End-Fire Antenna Array

An end-fire antenna array arrangement is the same as elements in the broadside arrangement however the main difference between these two configurations is the way of excitation. In this arrangement, the elements are generally fed out of phase with 180°, whereas in broadside arrangement each element is fed with the current of a similar phase. In this arrangement, the maximum radiation is attained along the array axis.

Thus, in order to get a unidirectional radiation pattern, this complete identical elements arrangement is simply energized with equivalent amplitude current, however, the phase changes continuously along the line. So, it can be stated that an end-fire array generates a unidirectional radiation pattern by the highest radiation occurring through the axis of the antenna array.

In the above radiation pattern diagram, the main distance between the elements within this arrangement is normally understood as λ/4 (or) 3λ/4. So these arrays are most frequently used in point-to-point communication & are appropriate for high, medium, and low-frequency ranges.

Collinear Array

In a collinear array, antenna elements are simply arranged in a single line from one end to the other which means one after the other. So this arrangement can be either horizontal or vertical orientation. The collinear array with a horizontal arrangement is shown below.

To all the antenna elements, the excitation is provided by currents of the same phase & magnitude to all the elements. Similar to a broadside array, this also provides radiation in the normal direction to the antenna array axis. Thus, the radiation pattern of the collinear array is somewhat related to the broadside antenna array.

This arrangement simply offers the highest gain whenever the elements are spaced at 0.3 to 0.5λ distance but this can cause constructional as well as feeding issues within the antenna array. So, the elements are arranged closer to each other.

The collinear array radiation pattern is shown above. It is to be noted here that with an increase in the length of the array the directivity also increases. Generally, two elements collinear array is generally used because it supports multi-band operation but sometimes, some applications utilize a combination of broadside, end-fire & collinear arrays because this enhances the directivity & gain to a very high range.

Parasitic Array

The multi-element arrays like parasitic antenna elements are arranged parasitically which provides maximum directional gain without feeding every array element. This kind of arrangement simply helps in dealing with the feed line problem by not providing direct excitation to every antenna array element. The parasitic antenna arrangement is shown below.

The elements which are not fed directly are known as parasitic elements & they simply draw their power from the emitted radiation by the driven element that is present nearby. As a result, parasitic elements are activated by electromagnetic coupling since the driving element is nearby.

The antenna array’s parasitic elements are not directly excited but they rely on the excitation delivered toward the driving element. So, the induced current within the parasitic element caused by the driven element is determined by the distance between these two elements & their tuning.

Thus, a unidirectional radiation pattern is produced with a ‘λ/4’ separation distance & 90° phase difference between the driving as well as parasitic elements. Thus, the radiation pattern of this array is simply created by a reflector arranged after the driving element, which includes back-reflected waves toward the forward wave. The range frequency for these types of antenna arrays ranges from 100 – 1000 MHz.

What is Antenna Array Gain?

The antenna array gain can be defined as the ratio of the intensity within a specified direction to the intensity of obtained radiation if a similar power is radiated with a single isotropic radiator.

What is the purpose of an antenna array?

The purpose of an antenna array is to transmit/receive radio waves by working as a single antenna.

What is a good antenna gain?

The good antenna gain is 3 dB, 6dB, etc.

What is an array in an antenna?

The array in an antenna is a group of antennas that are connected to form a single antenna.

What is the array factor of an antenna array?

An antenna array factor is a function of the antenna’s positions within the array & the weights used. So this factor can significantly change the directivity properties of the particular antenna element. So this phenomenon is mainly observed once antennas are connected together.

Advantages and Disadvantages

Antenna array advantages include the following.

• The strength of the signal increases very strongly.
• High directivity can be achieved.
• The minor lobes’ size is reduced drastically.
• Obtaining a high S/N ratio is possible.
• Large gains can be obtained.
• The amount of power wastage is reduced.
• Achieving better results is possible.
• The antenna array design simply supports the better performance of the antenna.

Antenna array disadvantages include the following.

• Antenna arrays are expensive.
• The resistive losses will be increased.
• It requires high maintenance.
• Mounting is difficult.
• It occupies a huge external space.

Applications

Antenna array applications include the following.

• An antenna array is very helpful in increasing overall gain, increasing the SINR (Signal to Interference plus Noise Ratio), canceling out interference, providing diversity reception, moving the array within a particular direction, measuring the arrival of incoming signals direction, etc.
• The antenna array is used in wireless, military radar, and satellite communications.
• These are utilized within the observation of astronomical.
• These are mostly applicable in long-distance communications & also mobile communications.
• These are used wherever high signal strength is required for long-distance transmission & reception.

Thus, this is an overview of antenna arrays – working with applications. An antenna array simply uses several antennas to capture & transmit signals in different directions. So antenna array is mainly used to increase the quality & range of our signal. Here is a question for you, what is the function of an antenna?