Corner Reflector : Working, Types, Calculation, radiation pattern & Its Applications

An antenna that is used to reflect the incident electromagnetic signals created from a separate source is called a corner antenna. These antennas work at higher microwave frequencies, so it is very popular in spacecraft antenna systems because of their features like; simple structure & its lightweight. These types of antennas are made with different reflectors whose plane is a parabolic, ellipsoid, hyperbolic (or) spheroid. There are different types of corner antennas like; plane, rod, corner, spherical, parabolic, and cylindrical. This article provides brief information on a corner reflector.

What is a Corner Reflector?

A passive device that is used for reflecting radio signals directly back in the direction of the emission source is known as a corner reflector. This is a retroreflector that includes three mutually perpendicular and intersecting flat surfaces that reflect waves directly to the source, although converted. The three intersecting surfaces in this antenna have frequently square shapes. This is a very useful device for the calibration of radar systems.

These reflectors are made of metal plates (or) wires that form right angles. These reflectors have the reflecting electromagnetic waves property which means they emerge as bright targets above the radar display even if they are off-axis or far away. These are used frequently as references or markers for radar measurements of speed, distance, position, or angle.

Examples of corner reflectors are Radar corner reflectors and optical corner reflectors. So the radar corner reflector is made with a metal that is used for reflecting radio signals from radar sets whereas optical corner reflectors (corner cubes/cube corners) are made with three-sided glass prisms that are utilized in laser ranging & surveying.

What is the Purpose of a Corner Reflector?

A corner reflector is used for generating a strong radar echo, particularly from objects otherwise that would have only very low effective RCS (Radar cross-section). This reflector has a minimum of two or above electrically conductive surfaces where these surfaces are mounted crosswise. If a corner reflector is larger, then more energy will be reflected.

How Does A Corner Reflector Work?

A corner reflector works by using the law of optics which means the signal after reflection moves in the similar direction from which it was obtained. More particularly, its operating principle is whenever an electromagnetic signal hits the corner reflector then the incoming signal will get reflected from every electrically conductive surface formerly that means, the wave for a dihedral structure is reflected two times whereas the wave in a trihedral structure is reflected three times. So the propagation direction of the waves will get reversed, so it reflects the wave within the direction from wherever these are invented & regarded as a passive device.

Reflectors are used mainly in antennas, so the main aim behind arranging a reflector within an antenna is to enhance its directivity. So the corner-shaped reflectors help to confine the radiated energy in the metallic plate and it provides an improvement within the directivity by reflecting the energy obtained within the preferred way.

Corner Reflector Antenna

A corner reflector antenna is a directional antenna that is used at UHF & VHF frequencies. This antenna was invented in 1938 by John D. Kraus. This antenna includes a dipole-driven element arranged before two flat rectangular reflecting displays joined at usually 90° of an angle. These antennas have 10 to 15 dB moderate gain, 20 to 30 dB high front-to-back ratio & wide bandwidth.

These antennas are used extensively for UHF television point-to-point communication links, receiving antennas, data links for WANs, and amateur radio antennas on the 144 MHz, 420 MHz, & 1296 MHz bands. These antennas radiate radio waves which are linearly polarized & can be mounted for either vertical or horizontal polarization.

Types of Corner Reflectors

There are two types of corner reflectors available; dihedral and trihedral which are discussed below.

Dihedral Corner Reflector

The corner antenna which has two surfaces on orthogonal planes is known as a dihedral corner reflector. This antenna has two plane reflectors which form 90* a dihedral angle. This type of reflector is formed whenever two conducting sheets are perpendicularly joined & this is used majorly in antennas. This corner reflector returns the wave to the emission source only if the incident beam direction is perpendicular to the intersection line of the planes. The wave in this type of reflector is reflected twice. These reflectors are sensitive to their mechanical arrangement thus more problems can occur.

Trihedral Corner Reflector

The corner antenna which has three surfaces on orthogonal planes is known as a trihedral corner reflector. This type of corner reflector can be formed by connecting three conducting sheets within a perpendicular orientation. The wave for a trihedral structure is reflected thrice & these reflectors are normally used within radar systems.

This reflector is very tolerant to being misaligned and this offers a simple method for fast field setup & calibration whenever required. The radio waves in this reflector strike the corner and are bounced by every surface area a total of three times to result in an upturned wave that transmits back to the source. So due to this, this reflector provides a high RCS (Radar Cross Section) target for testing the radar system, data & calibration for your application.

These reflectors are canonical radar reflectors commonly used for calibrating or determining the radar systems’ performance. These reflectors offer desirable attributes like; quite a large radar cross-section, a wide range of aspect angles by a large RCS, and Theoretical RCS simply calculated as a role of aspect angle.

Corner Reflector Radiation Pattern

The following figure represents the vertical corner reflector’s radiation pattern with the main axis. The radiation pattern in the antenna design field is the directional dependence of the radio wave strength from the antenna. This is a graphical representation of the far field antenna’s properties and also a variation of the radiated power by an antenna as a function of the route away from the antenna.

Corner Reflector Calculation

The corner reflector is a very helpful device for the calibration of radar systems. Generally, this reflector includes perpendicular plates which are intersected mutually. Generally, we can see the common corner reflectors are trihedral & dihedral.

Whenever the dihedral corner reflector is responsive to its mechanical alignment, then it is extremely tolerant to misalignment. So this provides a convenient method for a fast field system. This reflector is made simply with three right angle plates which are illustrated in the following figure.

Aeff = a^2 /√3

Where ‘a’ is the trihedral reflector’s side length.

The effective cross-section of radar can be measured by

σ = 4π a^4/3λ^2

Where the ‘λ’ from the above equation is the radar signal’s wavelength.

The waves in the trihedral corner reflector strike the corner reflector and are simply bounced through every surface 3 times to result totally in reversed direction waves transmitting back to the source. Thus, this corner reflector provides an extremely high RCS or Radar cross-section target mainly for testing radar systems & characterizations.

Advantages and Disadvantages

The advantages of corner reflectors include the following.

• The corner reflector at the lower end of the UHF band provides broad bandwidth gain.
• These reflectors have a high gain which means they transmit & receive signals above long
• If the corner reflector has more surfaces then the reflection will be stronger.
• These are suitable particularly to utilize on microwaves & ultra-high frequencies wherever structures 1 (or) two wavelengths within the highest overall dimensions are practical.
• Its construction is simple, easy to deploy, cheap & can be built readily to fold into a solid portable unit.
• They do not need any power source, calibration, or maintenance.
• These can be arranged in various orientations & locations.
• These can be used to replicate different kinds of targets like; vehicles, aircraft (or) buildings by changing their shape, number & size.
• Corner reflectors provide a reliable reference mainly for radar performance evaluation.
• These reflectors help in checking the sensitivity, accuracy, and resolution and to identify & correct any biases or errors in radar systems.

The disadvantages of corner reflectors include the following.

• The presence of a corner reflector makes the antenna arrangement quite bulky.
• The use of this reflector increases the cost of the corner reflector antenna.
• The corner reflector is not representative of radar validation mainly for real-world targets.
• The corner reflectors for radar validation may not capture the complete range of scenarios as well as challenges that the radar system may meet within practice.
• Corner reflectors for radar validation may interfere with other users (or) radar systems.
• These may create clutter (or) false alarms on the radar display or confuse or mask other objectives of interest. So they may also break regulations (or) permissions for utilizing the airspace or radar frequency band.

Applications

The applications of corner reflectors include the following.

• Corner reflectors are used within radar systems to hide the existence of defense motor vehicles from the opponent’s radar.
• These reflectors are also utilized within TV signal reception so find applications within home antennas.
• These are also widely used in optical communication applications.
• Corner reflectors are useful still for radar validation if properly & carefully used.
• These are used widely for UHF TV receiving antennas, data links for wireless WANs, point-to-point communication links & amateur radio antennas on the 1296 & 144, 420 MHz bands.
• These are used for reflecting radio or other electromagnetic waves directly to the emission source.
• These are used for generating a strong radar echo from different objects that would otherwise have simply extremely low effective RCS (Radar cross-section).
• These are utilized to make security reflectors for bicycles, signs & cars.
• These can also used for bouncing laser beams back toward the Earth from the moon’s surface.

Thus, this is an overview of a corner reflector, its working, types, advantages, disadvantages, and applications. This is a retroreflector with three mutually perpendicular and intersecting even surfaces, which replicates waves openly to the source. In this reflector, the three intersecting surfaces have square shapes frequently. These reflectors are simply made with metal that is used for reflecting radio waves from radar sets whereas optical corner reflectors are made with three-sided glass prisms which are used for surveying as well as laser ranging. Here is a question for you, what is an antenna?