The non-uniform radiation pattern suitable for the applications related to broadcasting. Generally, dipole antennas offer omnidirectional radiation pattern. While antennas like horn , helical , slot , etc. Thus, due to providing concentrated energy in one direction these suits point to point communication. We are aware of the fact that with an increase in the distance between transmitter and receiver, high directivity is needed. This is so because, with an increase in the distance, path loss also increases.
So, in case of large distance if attenuation is also high then it may be possible that the signal fails to reach the other end with the required strength. This is the reason, why high gain antennas are required. However, sometimes the gain of a single antenna fails to provide adequate transmission by overcoming the attenuation. We have already discussed that an antenna array is a combination of multiple antenna elements.
Antenna arrays are groups of isotropic radiators of electromagnetic frequency and energy. They provide a solution to the problems caused by single antennas. For instance, the dipole antenna allows better control of direction than an isotropic antenna, but as length the of the dipole increases, control direction may decrease.
More control and flexibility can be easily regained for beam direction with a multiple radiator arrangement. When arrays are arranged in straight lines, it is called a linear array, while antennas arranged in parallel lines on one plane have plane arrays in two dimensions. Numerous planes in a group of antennas results in a three dimensional array. The same orientation results in reinforcement of electric field intensity and ensures polarization in the same direction.
By: Justin Stoltzfus Contributor, Reviewer. First, the distance between each pair of elements can be tweaked, and of course the number of elements can be freely set.
An antenna array can have 2, 3, 4 … or thousands of elements. The feed network can also split the input power equally among all elements, or can implement more complex sharing methods.
Signal phase between elements can be adjusted too. Rather than a theoretical presentation, I propose in this article to illustrate the effect of each of these parameters one by one.
For that, I coded a small antenna array simulation software using Scilab—an open source, numeric programming language. The code is straightforward—no more than lines and annotated—and should be easy to read. The software then simply calculates the array factor—which is the effect of interferences—multiplies it by the theoretical pattern of a single element and generates some nice plots Figure 4. No electromagnetic simulation is involved, and just the effect of the array is simulated.
You probably figured out already that the distance between elements is directly linked to the wavelength. This means that a given antenna array—used at a frequency of say 1 GHz—will have exactly the same characteristics as an antenna array used at MHz 10 times less , if all lengths are multiplied by That means that each element will have to be 10 times larger, and that the distance between elements also will have to be multiplied to Two photos will be better than a long explanation of which antenna array uses the highest frequency.
It worked at MHz, so the elements were large and far from each other. Now look at Figure 6 , which is a reference design proposed by Texas Instruments TI for a 77 GHz antenna array for automotive radar applications. Do you see that higher frequencies means smaller elements and shorter distances between elements? Now, how to fix the distance between elements more precisely?
It can be set freely, but some distances are usually better than others. As explained above, waves cancel out if one wave is half a wavelength late compared to the other. The beam will be highly focused in one direction only.
A simulation will be helpful to explain this phenomenon. Look at Figure 7. Now, how many elements are needed? Simple—a greater number of elements gives a narrower main lobe and a higher gain. As an order of magnitude, an antenna built with 10 elements can provide a gain of about 20 dB, whereas a 1,element array can provide 30 dB, which means a main lobe 10 times narrower in surface. Look at Figure 8. If you check the simulated antenna pattern carefully, you will see that the main beam is narrower, and the gain is higher, when the number of elements is increased.
The amplitude of the side lobes is reduced too. The downside is that the antenna size is larger. This is unfortunately a rule applicable to all antennas—usually a larger antenna is better than a miniature one. An antenna array is a radiating system, which consists of individual radiators and elements. Each of this radiator, while functioning has its own induction field. Therefore, the radiation pattern produced by them, would be the vector sum of the individual ones.
The following image shows another example of an antenna array.
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