Lens Antenna : Design, Working, Types & Its Applications

An antenna is a metallic transmission device that transmits and receives radio electromagnetic waves in between the electric circuit & space. These devices are available in different sizes and shapes where the small antennas can be found on your roof used to watch TV and the big antennas are used to capture signals millions of miles away from satellites. There are different types of antennas available where every antenna is mainly designed for transmitting & receiving signals in a certain range of frequency based on its shape & size like wire, dipole, loop, short dipole, aperture, monopole, lens, slot, horn, etc. This article discusses an overview of one of the types of antenna namely – lens antenna, and its working with applications.

What is Lens Antenna?

The three-dimensional electromagnetic device that is used mainly for higher frequency applications is known as a lens antenna. This antenna includes an electromagnetic lens with feed and it is similar to a glass lens which is used in the optical domain. This antenna utilizes a curved surface for both transmission & reception. These antennas are fabricated with glass, wherever the converging as well as diverging lens properties are followed. The lens antenna frequency range ranges from 1000 MHz to 3000 MHz.

The function of a lens antenna is to generate a plane wavefront from spherical, control aperture illumination, collimate electromagnetic rays, forms the front of the incoming wave at its focus and produces directional characteristics.

Lens Antenna Design

Lens antenna is mainly designed to transmit and receive signals within the microwave frequency range. If we consider a converging type optical lens is present at a specific position & energy source is present at the focal point that produces the energy at a focal length distance along the optical lens axis in transmitting mode.

We all should be aware that from the optical point of view when the light drops on the outside of the lens then it twists because of the refraction. Here, the way of twisting of light energy mainly depends on the material & curve from where the lens is made.

As a result, whenever the feed antenna like a dipole or horn antenna is present at the focal point that is available on the left of the lens, the emerging spherical wavefront from the source which is deviating from nature can be incident from the antenna’s surface.

So, once the rays flow through it after the incidence, the deviating rays will collimate because of refraction & are changed into flat wavefronts. Thus, the parallel rays are attained at the right side of the optical lens. Like this, the antenna’s signal with a feed element is transmitted. Similarly, if this antenna is made with a dielectric material, then the RF electromagnetic signals are collimated in the same way & further they are transmitted.

Now consider the following antenna in receiving mode. In this mode, the parallel rays will incident on the converging lens surface, at the focal point on the left side of the lens converges because of the refraction mechanism. So, this process is used once it is utilized for receiving mode.

Here, it is to be noted that to attain better focusing properties at radio frequency, the medium must have a refractive index below unity. So this leads to giving straight wavefronts even once the material’s refractive index is low/high.

Lens Antenna Working

The lens antenna working is the same as an optical lens. In lens material, the microwave signals have a different phase velocity than in air, so the changing lens thickness simply delays the microwave signals transmitting through it in different amounts, the waves direction & changing the wavefront shape.

This antenna uses the properties of convergence & divergence of a lens to transmit as well as receive signals. These types of antennas include a dipole/horn antenna with the lens. Here, the lens size mainly depends on the operating frequency so when the operating frequency is higher, the lens is smaller in size. So at high frequencies, these antennas are used because, at lower frequencies, they can be somewhat bulky.

In a parabolic reflector, we have seen that the emitted energy from the feed element at the focus of the reflector reaches its surface then it changes the microwaves which are spherically radiated into plane waves. So it enhances the directivity.

In the same way in the case of a lens antenna, the point source performs like the feed that produces the microwave energy to the optical lens surface. So this optical surface powers the radiated spherical wavefronts to change into collimated one.

Here, it is notable that the collimating lens is made with a dielectric material that possesses the finite dielectric constant value. However, these can also be made with materials that exhibit below unity of refractive index at RF.

Lens Antenna Types

There are two types of lens antenna delay lens antenna and fast lens antenna which are discussed below.

Delay Lens Antenna

A delay lens or slow wave lens antenna can be defined as an antenna that causes retardation in the traveling wave fronts because of the lens media. Sometimes, these types of antennas are also called dielectric lenses. The representation of the dielectric lens action of the antenna is shown below.

In this type of antenna, the radio waves move very slowly in the lens medium than in free space, the refraction index is greater than one. Thus, the length of the path is increased by passing through the medium of the lens.

This is the same as an ordinary optical lens action on the light. Since solid parts of the lens enhance the length of the path, a converging lens like a convex lens focuses radio waves & a diverging lens like a concave lens disperses radio waves like in ordinary lenses. These lenses are made with dielectric materials & H-plane plate structures.

Delay lens antenna is classified into two types based on the dielectric material type used for construction: metallic dielectric lens and non-metallic dielectric lens.

Fast Lens Antenna

In a Fast lens or fast wave lens antenna, the radio waves move very faster within the lens medium as compared to in free space, thus the refraction index is below one, so the length of the optical path is reduced by passing throughout the lens medium. Sometimes, this antenna is also known as an E-plane metal plate antenna.

This type of antenna has no analog within ordinary optical materials, so it takes place due to the radio waves’ phase velocity within waveguides being higher than the light speed. Since solid parts of the lens reduce the length of the path, a converging lens like a concave lens focuses radio waves & a diverging lens like a convex lens is opposite to ordinary optical lenses. These lenses are made with E-plane plate structures and negative-index metamaterials.

Advantages and Disadvantages

The advantages of lens antenna include the following.

• It has narrow beam width, low noise temperature, high gain, and low side lobes.
• The structure of these antennas is more compact.
• These are less weight as compared to parabolic reflectors & horn antennas.
• It has better design tolerance.
• The feed & feed support in this antenna does not obstruct the aperture.
• The beam can be angularly moved with respect to the axis.
• It provides more flexibility within design tolerance, so twisting within this antenna is achievable.
• It is utilized for extremely high-frequency applications.

The disadvantages of lens antennae include the following.

• Lenses are bulky at lower frequencies especially.
• Complexity within the design.
• These are expensive for the same specifications as compared to reflectors.

Applications

The applications of lens antennae include the following.

• These are suitable for above 3 GHz frequency.
• Used like the wideband antenna.
• These are used mainly for microwave frequency applications.
• This antenna’s converging properties can be used to develop a high range of antennas called parabolic reflector antennas, so these are extensively used within satellite communications.
• These are utilized as collimating elements within high-gain microwave systems like radio telescopes, millimeter wave radar & satellite antennas.

Thus, this is an overview of lens antennae – working with applications. These antennas have mainly arrived to provide a solution to venue owners & operators by providing better mobile connectivity that is easier to deploy & less expensive. Here is a question for you, what is a horn antenna?