Helical Antenna: What’s So Intriguing About This Antenna?

A helical antenna is a radio, satellite, and space communication medium. These antenna machine devices are built with some specific feature that allows them to emit and receive very high frequencies.

Not only that, but a helical antenna can also offer maximum directivity with both high and low radiation modes. As a result, a helical antenna can also be used as a television broadcasting antenna.

But where else can this antenna be used? What are the structure, design, and properties of this antenna? What are the benefits and drawbacks of helical antennas? Read on to get your answers.

What is Helical Antenna?

A helical antenna is a UHF (ultra-high frequency) and VHF (very high frequency) antenna that is contemplated as a hybrid of the dipole and loop antennas. 

It’s constructed with unique features like high gain, circular polarization, and wide bandwidth. Hence, helical antennas are used in places where circular polarization is required.

This antenna contains a helix shape conducting wire. Generally, it’s set up over a ground plane along with a feed line that connects the antenna with the ground plane. 

However, the phase and current of the helix antenna may vary since it’s a wave-traveling antenna. These antennas are extensively used for practical applications for their exceptional prosperities, for example, satellite and radio communications.

Basics Of Helical Antenna

Helical antennas are the invention of a famous American physicist, John Daniel Kraus, in 1946. He was also well-known in America for his contribution to radio astronomy, antenna theory, and electromagnetics.

John D. Kraus’s work invented semi-empirical design formulas for high gain, bandwidth, axial ratio, input impedance, and main beam shape depending on the antenna array theory and vast measurements.

Why is Helical Antenna Important?

Helical antennas are different from other types of antennas. For instance, this antenna supports wide bandwidths and can receive and transmit very high-frequency waves, particularly for ionospheric propagation.

These antennas are important for communicating within different mediums, such as satellites, space telemetry, space, and radio astronomy. In fact, helical antennas are equally important for satellites like weather reading and data relay.

In addition, it responds to and emits electromagnetic waves, including circular polarization. Besides that, these antennas provide the benefits of high gain over a broad extent of frequencies which makes these preferable for broadband satellite communication.

Types Of Helical Antennas

The types of helical antennas are determined by how many wires the antenna contains. For example,

• Monofilar

If the antenna is built with one helix shape wire, it falls under the type of Monofilar Helical Antena. This helical antenna offers a high gain advantage in an axial direction. It generally works over a vast frequency range; hence, broadband satellite communications use a Monofilar helical antenna. 

• Quadrifilar

Unlike the first antenna, helical antennas that are built with two or more wires are called Quadrifilar or Bifilar Helical Antenna. This type of helix antenna is widely used for ground-to-air communication as a base station antenna. With this antenna, they don’t need multiple antennas for air communication.

Structure Of Helical Antenna

A helical antenna is utilized for circular polarization in a wide variety of bands, such as UHF and VHF. This antenna is mostly used in axial operating mode, which is wideband. It’s because the beamwidth and efficiency in the normal mode of operation are small.

The whole structure of this antenna is simple yet contains maximum directivity. However, depending on the axial ratio, the polarization may vary.

For example, linear horizontal polarization occurs when the axial ratio is zero, whereas an infinite axial ratio can create linear vertical polarization. Again, circular polarization occurs when the ratio of the axial is one.

Radiation Of Helical Antenna

This antenna is mostly used in wireless networking and space communication for its wider bandwidth and high-frequency feature. Generally, the wave radiation of a helix antenna ranges between 30MHz to 3GHz.

Designing Of Helical Antenna

The design of the helical antenna is simple. Usually, this antenna is designed with a thick copper wire in the shape of a helix. The conducting wire is connected through the feeder line with the ground plate.

One helix end of the wire is attached to the middle conductor. In contrast, the external conductor is connected to the ground plate. 

This antenna works in two modes: axial and normal mode. However, the distances between the consecutive spins and the helix diameter determine the antenna’s operating mode.

For instance, if the single turn length is considered as L and the consecutive turn space is S, then the total antenna length will be NS. And the antenna circumference is considered as C and is denoted as πD.

The radiation of this antenna is primarily based on the diameter, pitch angle, and turning space. Hence, the pitch angle is the angle between the plane and the helical wire from the tangent line.

Thus, the pitch angle in this antenna is

a = tan-1 (S/πD)

Here,

a = Pitch angle

S = Turn spacing

D = Helix diameter

So we can say that the design of the radiation characteristics of the helical antenna is altered by changing the above parameter depending on the wavelength.

Properties Of Helical Antenna

To understand the properties of a helical antenna, you need to look at how it works. Generally, the coaxial cable of this antenna can function in normal and axial modes.

It’s necessary to know that the antenna can operate in multiple modes, but here we will discuss the only two prominent modes.

• Normal Mode

It’s also called Perpendicular mode. In normal radiating mode, the maximum radiation is released toward the plane perpendicular to the antenna’s axis, and the waves create circular polarization.

It means the radiated field is high toward the plane perpendicular and low toward the axis. However, the antenna dimension in this mode is smaller than a wavelength, which offers narrow bandwidth and low radiation efficiency.

The helix of this mode of radiation resembles the mixture of a short dipole and a small loop. Hence, the radiation pattern is also similar to the resembles of helix pattern. As these are compact antennas, normal helical radiation is used for operating on UHF bands in portable devices like mobile.

• Axial Mode

This axial-mode helical antenna offers indistinguishable diameter and pitch from the wavelength. Consequently, this mode works like a directional antenna.

Unlike the normal mode, it’s critical to determine the radiation properties of this mode. This mode of radiation is also known as the end-fire mode and maximum radiation release toward the helix axis. Hence, the radiation pattern of this antenna technology is almost circular.

The spacing between loops and the circumference of the axial mode is similar to one wavelength. As a result, this radiation mode can produce wide and highly directional beams, which makes them preferable for practical uses.

Advantages Of Helical Antenna

Some of the advantages of the helical antenna are as follows:

• Simple Design

The antenna design and structure are simple and highly directional. Hence, it’s best for use in telemetry, radio astronomy, space, satellite relays, and air communication.

• Polarized Antenna Simple Design

A helical antenna mostly operates in a circular polarised pattern. Due to this feature, this antenna technology accepts both vertical and horizontal polarized antennas.

• High Frequency

The most prominent advantage of helical antennas is that they can receive and transmit ultra-high frequencies.

Disadvantages Of Helical Antenna

Here are some disadvantages of a helical antenna:

• Large And Expensive

This antenna is large, and the antenna implant needs a spacious place. Besides, the price of this antenna is higher compared to other types. However, the radiation efficiency of the helical antenna decrease when the number of turns increases.

Applications Of Helical Antenna

Here are some common places of helical antenna application:

• Widely utilized in space communication through electromagnetic waves and maximum directivity.
• Used at earth stations for satellite communication.
• It can be used for telemetry links in the case of ballistic missiles and radio astronomy.
• To transmit and receive VHF signals, particularly for ionospheric propagation.
• To build communication between the earth and the moon.

FAQs

Conclusion

So, you now have ideas about what is a helical antenna, how it works, its structure and design, and where this antenna is mostly used. 

Among multiple types of antenna types, this one is mostly used for space, air, and satellite communication, thanks to its high directivity, circular polarization, and ability to transmit and receive high waves.

Read more:

• spiral antenna
• yagi-uda antenna