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An Introduction to Planar Array Antennas

Tamara Wilhite is a technical writer, industrial engineer, mother of two, and published sci-fi and horror author.

What Is a Planar Array Antenna?

A planar array is an antenna made up of several other antennas in an array. Each set of antennas is connected and works together as a single antenna. They may be used to transmit or receive signals. The individual antennas or elements are generally fed power in a phase relationship. This may cause constructive or destructive interference.

When you have constructive interference, the antenna array is far more efficient than a single antenna would be. Destructive interference is never intentional, but they may try to put interference in the null portion of the antenna portion. That is called null steering.

Is a Planar Array Antenna the Same Thing as a Planar Antenna?

The short answer is no. A planar antenna is an antenna that puts the active and parasitic elements on a single plane. This makes the planar antenna two-dimensional. Planar antennas are often wideband antennas. And antennas could theoretically be assembled into a planar array, though most are not.

Planar antennas

Planar antennas

What Are the Benefits of Planar Array Antennas?

They have the most gain for a given area. A dish is typically 50-60% efficient. Planar Arrays can be 80% efficient. The feed for a dish tends to concentrate most of the energy in the center of the dish, so the illumination is not uniform. A lot of the energy sent to the edge of a dish misses and is lost. Yet this is what makes dish antennas popular in aircraft radars, since they are small enough to fit in a nose cone and still be aerodynamic. But if you have space, planar arrays win.

A planar array antenna is by definition made up of several similar antennas lined up to form an array. By making the antennas different shapes, you can generate different patterns using the same underlying infrastructure.

Because you can steer the signal from a group of antennas, you can change the direction a few degrees to minimize interference. This is called path diversity.

How Are Planar Array Antennas Used?

Planar arrays are often used in radar. Military phased array radars may be composed of thousands of individual antennas networked together.

Antennas for RFID readers often require the fan beam that a planar array antenna can generate.

The SCR-270 radar antenna was part of a mobile radar system, operating at 104 MHz, that could detect and track aircraft at 125 miles.

The SCR-270 radar antenna was part of a mobile radar system, operating at 104 MHz, that could detect and track aircraft at 125 miles.

How Would a Planar Array Antenna Work?

Let’s say you have an array of 10 patch antennas. Each patch antenna is one inch high and one or two inches wide. In an array, the number of antennas matters more than their individual size. You now have a fan beam that is broad left/right and narrow up/down.

Planar array antennas are commonly used in cell sites to create a beam that is concentrating the energy at the horizon but is still 90 or 120 degrees wide. (Antennas this wide are called sector antennas.) With a planar array antenna, 3 or 4 antenna arrays or sector antennas can provide 360 degree coverage.

With phase adjusters, the beam from the antenna array can be steered. Switch in an extra feed line to the elements on the left side of the array, and the beam will steer to the right. Most cell site antennas have phase adjusters that will swing the beam up or down a few degrees. This is used to adjust coverage areas. A mechanical adjustment would move the antenna array a few degrees.

Antennas that are steered electronically via a phase shifter may be called phased array antennas. This technology is so common that the term phased array antennas may be used to refer to all array antennas.

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