What is an Antenna Array?
An antenna array is a group of antennas joined together and arranged in a regular pattern to form a single antenna capable of producing radiation patterns that individual antennas cannot. As the antennas are constructed as an array, sufficient spacing and phase must be given.
Since, most signals distort while travelling from one end to the other, antennas that transmit a signal over a longer distance must have a high directional gain.
Despite its strong directive, a single antenna fails to send the signal to the receiver without losses. The antenna array is employed for this reason. The orientation of elements inside the antenna array is used to classify the antenna array. The antenna array is classified based on how various antennas are arranged in the design.
Classification of Antenna Array
- Broadside Array
- End-fire Array
- Collinear Array
- Parasitic Array
Broadside Array
A broadside antenna array is a kind of configuration of several identical elements aligned parallel along the line corresponding to the antenna axes. It is well acknowledged to be the most extensively utilized feasible antenna array arrangement.
Figure 1 shows the schematic arrangement of Broadside Antenna Array. In this configuration, the elements are arranged horizontally at identical distances from one another, and each element is supplied a current of the same magnitude and phase.
As the elements in this arrangement are activated, the broadside (i.e., the direction normal to the array axis) emits the most radiation, whereas the other directions generate very little radiation. As a result, the radiation pattern is bidirectional. Because it radiates in both directions along its broadside, it has a bidirectional radiation pattern. The broadside is thus defined as the arrangement that has the direction of the main radiation in parallel to the array axis and the placement plane of the antenna.
The radiation pattern of the broadside antenna setup is depicted in the above diagram. As a result, there will be a vertical radiation antenna pattern for horizontal alignment of the elements.
In order to transform the bidirectional radiation pattern into a unidirectional radiation pattern, accomplish it by placing a replica array at a distance of roughly λ/4 behind the original array and stimulating it with a current with a 90° phase lead.
The number of parts in the arrangement is often determined by the amount of space available, as well as the necessity for beam width and cost. The array's length is set to be between 2λ and 10λ.
A reflector antenna is sometimes used in conjunction with a broadside array to help reflect the back transmitted wave and add the minor lobe to the major lobe. This boosts the antenna's gain and directive while also providing a unidirectional radiation pattern.
End-Fire Array
The elements in an end-fire array are arranged similarly to those in a broadside array, but the difference between the two configurations is in the method of excitation. In an end-fire array, the elements are fed 180° out of phase, whereas in a broadside array, each element is fed with the same phase current. The highest radiation is obtained along the array axis in this configuration.
As a result, in order to have a unidirectional radiation pattern, this entire arrangement of identical elements is excited with an equal amplitude current, but the phase varies continuously along the line. In simple terms, the phase difference between the pieces must vary progressively in proportion to the distance between them.
As a result, it can be stated that an end-fire array produces a unidirectional radiation pattern, with the maximum radiation occurring along the array's axis.
The above figure shows the radiation pattern of End-Fire Array. The distance between the pieces in this arrangement is usually interpreted as λ/4 or 3λ/4. These arrays are most commonly employed in point-to-point communication and are suitable for low, medium, and high-frequency ranges.
Collinear Array
The name implies that it is an arrangement that permits multiple antenna elements to be placed in a single line from one end to the other. This means that the various pieces are placed in a single line one after the other. This configuration result can be oriented vertically or horizontally. The horizontal configuration of the collinear array is shown in the above diagram.
Excitation is likewise delivered to all of the elements with currents of the same amplitude and phase. This array, like the broadside array, provides radiation in the direction normal to the array's axis. As a result, its emission pattern resembles that of a broadside array. This array, on the other hand, has circular symmetry across the primary lobe, allowing it to emit omni-directional radiation.
The components are placed at a spacing of around 0.3 to 0.5λ, this layout provides the best gain, but it causes construction and feeding issues in the array. As a result, the parts are positioned closer together.
The above figure shows the radiation pattern result of Collinear Array. It's important to note that the directivity of the array increases as the length of the array grows. In most cases, for the multi-band operation a two-element collinear array.
Parasitic Array
Parasitic arrays are multi-element arrays that provide high directional gain without feeding each array element. By not delivering direct stimulation to each element of the array, this antenna array helps to solve the feedline problem. Its operation is based on parasitically feeding some parts of the antenna array. The parasitic configuration of antennas is depicted in the above diagram.
The elements that are not directly fed are known as parasitic elements, and they draw their power from the radiation emitted by the driven element that is present nearby. As a result, parasitic elements are activated by electromagnetic coupling since the driving element is nearby.
This simply means that the parasitic elements of the antenna array are not excited directly and instead rely on the excitation delivered to the driving element. It should be mentioned that the induced current in the parasitic element caused by the driven element is determined by the distance between these two elements as well as their tuning.
As a result, a unidirectional radiation pattern is produced with a separation distance of about λ /4 and a phase difference of 90° between the driving and parasitic elements. As a result, this array's radiation pattern is created by a reflector placed behind the driving element, which adds back-reflected waves to the forward wave.
The figure shows the radiation pattern of Parasitic Array. The frequency range for these antenna arrays is 100 to 1000 MHz. As a result,it has a high directed gain and emits a unidirectional radiation pattern from the driven to parasitic element.
Phased Array Antenna
Electronic steering allows phased array antennas to modify the direction and form of emitted signals without requiring the antenna to move physically. This electrical steering is caused by the phase difference between the signals transmitted by each antenna in the array.
The phase-dependent superposition of two or more emitted signals is the underlying principle of the phased array antenna. When the signals are in phase, they combine to generate an additive amplitude signal. When the signals are out of phase with each other, they cancel each other out.
Phased array antennas are classified into three types:
- Linear array
- Planar array
- Frequency scanning array.
Antenna Calibration
The methodology of radiated emission measurements is directly affected by the antenna factor's accuracy. Antennas are calibrated on a regular basis to ensure that measurement findings are accurate and traceable.
Antenna Calibration is the process of setting up an instrument such that it can produce a result for a sample that is within a reasonable range. When samples of unknown values are evaluated in the routine use of the product, the instrument can therefore deliver more accurate results.
The objective of Antenna calibration is to ensure the accuracy of testing antennas in order to reduce measurement errors. Antenna Calibration reduces experimental error and uncertainty to an appropriate standard by quantifying and controlling them.
Types of Antenna Calibration
- Electrical Antenna Calibration
- Mechanical Antenna Calibration
- Temperature Antenna Calibration
- Pressure Antenna Calibration
Advantages of Antenna Array
- The signal strength grows stronger.
- It is possible to achieve high directivity.
- The size of the minor lobes is drastically reduced.
- It is possible to get a high signal-to-noise ratio.
- It is possible to obtain a large gain.
- The amount of energy wasted is minimized.
- It is possible to achieve better results.
Related Concept
- Antenna parameters and Antenna Calibration
- Phased Array Antenna
- Radar system- Antenna parameters
- Phased Array Beam forming ICs Simplify Antenna Design
Common mistakes
- Design of antenna Array must be done with care.
- The array elements' geometrical layout and spacing must be taken into consideration.
- The different elements' excitation amplitude and phase must be calculated correctly.
- The order in which the individual elements are arranged must be considered.
Context and Applications
- Used in satellite communications
- Used in wireless communications
- Used in military radar communications
- Used in the astronomical study
Academic Applications
- Bachelor of technology of Electrical Engineering
- Masters of technology of Electrical Engineering
- Bachelors of Electronics and communications engineering
- Masters of Electronics and communications engineering
- Radar Engineering
Practice Problems
Q1. Which one is the type of Antenna array?
A. Broadside Array
B. End-fire Array
C. Collinear Array
D. Parasitic Array
E. All of the above
Answer: E
Explanation: The types of antenna array are broadside array, end fire array, collinear array and parasitic array.
Q2. When the antennas are constructed as an array, sufficient ............. and .......... must be given.
A. Space and Phase
B. Radiation and Phase
C. Space and Radiation
D. None
Answer: A
Explanation: When the antennas are constructed as an array, sufficient spacing and phase must be given.
Q3. .............................. array the elements are arranged horizontally at identical distances from one another, and each element is supplied a current of the same magnitude and phase.
A. Broadside Array
B. End-fire Array
C. Collinear Array
D. Parasitic Array
Answer: A
Explanation: Broadside array the elements are arranged horizontally at identical distances from one another, and each element is supplied a current of the same magnitude and phase.
Q4. In ....................... the elements are fed 180° out of phase, whereas in a broadside array, each element is fed with the same phase current.
A. Broadside Array
B. End-fire Array
C. Collinear Array
D. Parasitic Array
Answer: B
Explanation: In an end-fire array, the elements are fed 180° out of phase, whereas in a broadside array, each element is fed with the same phase current.
Q5. The frequency range for ........................... antenna arrays is 100 to 1000 MHz.
A. Broadside Array
B. End-fire Array
C. Collinear Array
D. Parasitic Array
Answer: D
Explanation: The frequency range for these antenna arrays is 100 to 1000 MHz.
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