# What Is an Exponential Horn Antenna?

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

## What Is An Exponential Horn Antenna?

An exponential horn antenna, also called a scalar antenna, is a type of horn antenna. Horn antennas have a funnel or horn shape. The cross-sectional area of the opening follows an exponential function. This maximizes energy emitted and minimizes the reflections inside the antenna.

## What Shapes May a Horn Antenna Have?

That horn may follow a pyramidal or conical shape. The pyramidal shape has a trapezoidal cross-section. The ridged horn has exponentially opening metallic bars; the ridges in the antenna lower the cut-off frequency and increase its bandwidth. Other horn antennas, such as an exponential horn antenna, often have a cross-section similar to a Vivaldi antenna.

## Ridged Horn Example

## What Are Exponential Horn Antennas Used For?

Horn antennas are designed for higher frequency ranges like UHF bands. Exponential horn antennas like other horn antennas work well as microwave antennas, and they can be used for millimeter wave applications. This makes exponential horn antennas common in short range radar systems like speed enforcement systems.

They can be used as antennas or radiators to feed a reflector antenna such as a parabolic antenna. The horn acts as a flared waveguide.

Because exponential horn antennas have consistent performance over a wide frequency range, they are often used for EMC or electromagnetic compatibility measurement applications.

Exponential horn antennas have been used in ground penetrating radar (GPR) systems and free-space time-domain measurement systems.

A 2017 IEEE paper discussed using a circular ring to create a unidirectional antenna that could allow these antennas to be used bridge outdoor WLAN systems, but they are not normally used for 2.4 GHz wireless networking applications.

## Vivaldi Antennas

## Is a TEM Horn Antenna an Exponential Horn Antenna?

A TEM horn antenna may have a linear tapered metal plate or exponential tapered metal plates. In short, a TEM horn antenna may be an exponential horn antenna, but not all are.

## What Are the Benefits of Exponential Horn Antennas?

All horn antennas have moderate to high gain. The very large aperture of the exponential horn antenna gives them incredibly high gain. To maximize gain, the taper should be so long the phase of the wave-front is constant. However, there is a point where the increase in length isn’t worth it for the relatively small increase in gain.

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Exponential horn antennas have a low SWR or standing wave ratio, and they have almost no internal reflections.

Horn antennas like exponential horn antennas have low return loss.

Because horn antennas don’t have a resonant element, they have wide bandwidth. In short, they operate over a wide frequency range. Furthermore, the impedance for these antennas is constant over a wide frequency range. Impedance matching is much more efficient with a horn antenna.

These antennas are easy to interface to a waveguide, and they can be designed with a transition so that you can use them with a coaxial feeder.

## What Are the Weaknesses of Exponential Horn Antennas?

Exponential horn antennas, like other horn antennas, are directional. The horn’s shape impacts its directivity and performance. While horn antennas are relatively easy to manufacture, exponential horn materials are larger and use more material than pyramidal and purely conical antennas.

## Questions & Answers

**Question:** I‘m very interested in the detailed calculations on exponential horns of circular or square cross-section. Could you provide some references? My interests are more theoretical than practical, so the mathematical formulas are of more interest to me than measurements.

**Answer:** I know that WA5VJB's website has a lot of practical examples of how to make horn antennas and other types of antennas. I don't think it gets that deep into the equations.

**© 2018 Tamara Wilhite**

## Comments

**Tamara Wilhite (author)** from Fort Worth, Texas on December 28, 2018:

Thank you RTalloni.

**RTalloni** on December 28, 2018:

So enjoy your informational posts. This on exponential horn antenna is a great introduction for someone like me. Looking forward to showing it to my husband who will find it even more interesting. Happy New Year to you and yours!