03 Nov
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Antenna is a device that receives or transmits radio waves effectively. A helical antenna is a kind of antenna that includes a helical radiating element. This antenna is used at both UHF and VHF frequencies where circular polarization is an important thing. This blog explains the Helical Antenna in detail with its features, benefits, and disadvantages.
A helical antenna is developed with the help of conducting wire-wound in a helical structure form. This antenna is used in ultra-high frequencies. Apart from that, the helical antenna also has some different features such as circular polarization and high gain.
Normally, the frequency range of this antenna is between 30MHz and 3GHz. It is widely used in many applications such as wireless networking, radio astronomy, and satellite communication.
We discussed what is helical Antenna in the above section. Now, let us discuss some of the best features of this antenna in the below section:
A helical antenna is a very simple antenna that contains a helical radiating element. Now, we will further discuss the major benefits of a helical antenna in the following section:
Just like benefits, the helical antenna has many disadvantages such as:
A helical antenna is developed with the help of conducting wire-like thick copper wire wound in a helical form. It is connected to the ground plate via a feeder line. The simple design of a helical antenna offers waves that are polarized circularly. For this reason, the helical antenna is widely used in various communication-based applications where satellite relays are involved.
Helical antennas operate in 2 modes where the deciding factor is the diameter of the helix and spacing between 2 consecutive spins. The radiation of this antenna depends on the turn spacing, pitch angle, and diameter. The pitch angle is the existing angle between a line tangent to the helix wire and a plane normal to the helix axis.
The current supplies in the conducting wire as the conductive wire in a helical antenna is excited through a coaxial cable or 2-wire transmission line. It causes the field lines generation and emission of radiations. This antenna might emit in various modes. The operation modes of a helical antenna are axial mode and normal mode. Now, let us discuss both the modes in detail in this section:
In the normal mode, both the diameter and pitch of a helical antenna are small as compared to the wavelength. The operation is analogous to the monopole or electrical short dipole. In normal mode radiation, the field of radiation is normal to the helical antenna, and the radiated signals are polarized circularly.
In addition, the normal mode has a narrow bandwidth and low efficiency. Because of these features, the antenna is widely used for UHF TV broadcasting antenna and mobile radios. The radiation pattern in a helical antenna is the combination of short dipole and loop antennas.
The radiation pattern of an antenna in the normal mode depends on the turn spacing and diameter values. However, the normal mode operation is not used often because of a narrow bandwidth and low radiation efficiency.
In axial mode, the diameter and pitch of a helical antenna are similar to wavelength. It works similarly to a directional antenna. This mode does not have a simple solution to decide the radiation properties. It is widely used in satellite communication systems and earth-based stations.
A helical antenna is widely used in many applications such as:
This is all about a helical antenna, its features, benefits, and disadvantages. You can get the best helical antenna from the manufacturers online by filling out the online form. Look at the different quotes and compare the prices of the various products.
A helical antenna is available in different sizes as per the needs of the customers. You can choose the affordable antenna for your need from online websites.
03 Nov
According to IEEE standard, an antenna or radiator can be defined as a medium that is used to transmit and receive radio waves. There are different types of antennas available which are categorized into different types based on the application like horn antenna, dipole, patch, broadband, log-periodic, etc. Among them, helical antenna is one of the types of broadband antenna which is also called helix antenna. This is one of the most primary, realistic & straightforward antennas which are designed with conducting wire-wound in a helical structure form. So, this article discusses an overview of a helical antenna and its working with applications.
Definition of helical antenna: The simplest antennas which are used widely in ultra-high frequencies are known as helical antennas, so this antenna works in VHF & UHF ranges. These antennas are designed with conducting wire in a helix shape. This antenna has some unique characteristics like wide bandwidth, high gain & circular polarization.
The frequency range of this antenna ranges from 30MHz0-3GHz. This antenna is used in space communication such as satellite relays and also in radio astronomy, wireless networking & satellite communications.
The salient features of a helical antenna include the following.
The construction of the helical antenna is shown below. This antenna can be designed with a conducting wire-like thick copper wire wounded in helical form & it is connected to the ground plate through a feeder line. This antenna is very simple to design and it provides waves that are polarized circularly, so it is used in different communication-based applications where satellite relays are involved.
The above diagram depicts a helical antenna system that needs wider outdoor space. Here, one helix end is connected to the middle conductor of the cable whereas the external conductor is simply connected to the ground plate which is made with the conductor. This antenna is fed by a coaxial cable which can be functioned in axial & normal modes.
We know that the helical antenna operates in two modes where the deciding factor of these modes is the diameter of the helix & spacing between two consecutive spins.
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Suppose, the length of a single turn of the helical antenna is L, the spacing between consecutive turns is S, then the whole antennas length will be NS. The helix circumference is denoted with C that is given as πD. Here, D is the helical spring diameter.
When we consider the one unrolling turn of the helix antenna, then the different parameters which are related to it can be defined through the following triangle. The helical antennas radiation mainly depends on the turn spacing, diameter & pitch angle. So, the pitch angle is the existing angle in between a line tangent to the helix wire & plane normal to the helix axis.
So, tan α = S/C = S/ πD =>
Pitch angle in a Helical Antenna α = tan-1 (S/πD)
Where,
D is the helix diameter.
S is the turn spacing
α is the pitch angle.
Therefore, finally, we can conclude that the antenna radiation characteristics are modified by changing the above parameters based on the wavelength.
Once a conductive wire in an antenna is excited through a coaxial cable otherwise two-wire transmission line then-current supplies throughout the conducting wire. So, this causes the field lines generation & emission of radiations. It is important to know that a helical antenna may emit in different modes, so modes of operation of the helical antenna are normal mode and axial mode which are discussed below.
In this type mode, both the pitch & the diameter of the helix antenna are tiny as compared to the wavelength. So, its operation is analogous to an electrical short dipole or monopole. In radiation of normal mode, the field of radiation is normal to the helix axis so, radiated signals are polarized circularly.
This mode has low efficiency & narrow bandwidth, so used mainly for compact antennas for portable, two-way mobile radios & UHF TV broadcasting antennas. The helical antennas radiation pattern is a combination of both the loop & short dipole antennas.
The radiation pattern of the helical antenna in the normal mode of radiation mainly depends on the diameter values and its turn spacing. The main disadvantages of normal mode operation are, narrow bandwidth, low radiation efficiency thus, it is not frequently used.
In this mode, both the pitch and diameter of the helix antenna are similar to the wavelength, so it works like a directional antenna. Not like the normal mode, there is no simple solution available to decide the radiation properties in this axial mode. Thus for this mode, experimentally determined analytical & numerical methods are used to conclude these factors. This mode is frequently used through earth-based stations within satellite communications systems. This mode of operation is used more practically.
The following formulas are used for calculating helical antenna gain, diameter, space between coils, wire length, half-power beamwidth, beamwidth first nulls, and appearance.
Helical Antenna Gain (G) = (10.8+10 x log (number of turns x space between coils)) / log10
Diameter (D) = wavelength/3.14
Space between coils (S) = Space between coils x wavelength
Length of wire (L) = Number of turns x (wavelength^2 + Space between coils^2
Half Power Beam Width of antenna = 52 / ((Number of turns x space between coils))
Beam Width First Nulls of antenna = 115 / ((Number of turns x Space between coils))
Aperture = (10(Antenna Gain / 10) x wavelength^2 ) / (4 * 3.14)
The advantages of a helical antenna include the following.
The disadvantages of a helical antenna include the following.
The applications of helical antennae include the following.
Thus, this is all about an overview of the helical antenna and its working with applications. These are very simple antennas where the conducting wire of this antenna is wounded in helical form & connected to the ground plate through a feeder line. The polarization of the helical antenna is circular and also has high directivity, so used in satellite & space communications.
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