In this modern wireless communication system, many engineers are showing interest to do specialization in communication fields, but this requires basic knowledge of communication concepts like types of antennas, electromagnetic radiation and different phenomena related to propagation.
we will start learning about Antennas, what are the different types of antennas, different properties of antennas and many other important aspects of antennas.
If you are interested in Wireless Communication Engineering, there will be a time where you will come across designing or working with antennas. Irrespective of the field of interest, I hope that this tutorial on Antennas and different types of Antennas will be useful to even a non-technical person.
- A whole lot of complex mathematics involved in the theory of Antennas beginning with electromagnetic waves, Maxwell’s Equations, power patterns, radiation, etc.
- Discussing those is out-of-scope of this tutorial as this is just an introductory work.
Properties of Antennas
- The radiation pattern is a plot of radiated power in different directions.
- The anisotropic antenna radiates equally in all directions
- Directivity can be expressed in dB compared to a half-wave dipole(0 dBd =2dBi).
For Electrical Properties
- Antenna Gain
- Directivity and bandwidth
- Effective length
- Polar diagram
- Front/Back ratio
- Power capability
For Mechanical Properties
- Connector Types
- Working temperature
Different Types of Antennas
Now that we have seen a little bit about antennas in general and why do we use antennas, let us proceed further and take a look like various types of antennas. There are several types of antennas and each literature work has its own classification of antennas.
Some of the common types of antennas are mentioned below:
- Wire Antennas
- Short Dipole Antenna
- Dipole Antenna
- Loop Antenna
- Monopole Antenna
- Log Periodic Antennas
- Bow Tie Antennas
- Log-Periodic Antennas
- Log-Periodic Dipole Array
- Aperture Antennas
- Slot Antenna
- Horn Antenna
- Microstrip Antennas
- Rectangular Microstrip Patch Antenna
- Quarter-Wave Patch Antenna
- Reflector Antennas
- Flat-plate Reflector Antenna
- Corner Reflector Antenna
- Parabolic Reflector Antenna
- Lens Antennas
- Travelling-wave Antennas
- Long Wire Antenna
- Yagi–Uda Antenna
- Helical Wire Antenna
- Spiral Antenna
- Array Antennas
- Two-Element Array Antenna
- Linear Array Antenna
- Phased Array Antennas
Let us now briefly see about a few of these different types of antennas.
Wire antennas are also known as linear/curved antenna.
One of the most commonly used antennas is wire antennas. They can be found in vehicles (automobiles), ships, aircraft, buildings, etc. Wire Antennas come in different shapes and sizes like straight wire (Dipole), Loop and Helix.
Short Dipole Antenna
Perhaps the simplest of all antennas are the Short Dipole Antenna. It is a special case of the Dipole antenna.
In its simplest form, it is basically an open circuit wire with the signal being fed at the center. The term “short” in short dipole antenna doesn’t directly refer to its size but rather to the size of the wire relative to the wavelength of the signal
A Dipole is deliberated as short if the length of the radiating element is less than a tenth of the wavelength.
The short dipole antenna is made of two co-linear conductors that are placed end to end, with a small gap between conductors by a feeder.
The short dipole antenna is infrequently satisfactory from a proficiency viewpoint because most of the power entrance this antenna is decreased as heat and resistive losses also become slowly high.
A Dipole Antenna is made up two conductors in the same axis and the length of the wire needs to be small compared to the wavelength.
The dipole antenna is consists of two metallic rods through which current and frequency flow. This current and voltage flow created an electromagnetic wave and the radio signals get smeared. The antenna consists of a radiating element that slit the rods and makes current flow through the center by using a feeder at the transmitter out that takes from the receiver. The different types of dipole antennas used as RF antennas include half wave, multiple,non-resonant, and so on.
A Loop antenna is formed by single or multiple turns of wire forming a loop. The radiation produced by the loop antenna is comparable to a short dipole antenna.
The circumference of the loop antenna determines the efficiency of the antenna is similar to that of dipole and monopole antennas. These antennas are two types: electrically small and electrically large based on the periphery of the loop.
Electrically small loop antenna———> Circumference≤λ⁄10
Electrically large loop antenna ———> Circumference≈λ
A special case of Dipole antenna is the monopole antenna i.e. it is half of the dipole antenna. A monopole antenna is half of a simple dipole antenna located regarding a grounded plane as shown in the figure below.
The graphical record on the grounded plane is going to be almost like the half-wave aerial, however, the whole power radiated is half that of a dipole the field gets radiated only in the superior hemisphere region. The radial asymmetry of those antennas become double compared to the dipole antennas.
The monopole antennas are used as vehicle-mounted antennas as they provide the required ground plane for the antennas mounted on the earth.
A log-periodic antenna is additionally named as a log-periodic array. It is a multi-element, directional narrow beam antenna that works on a broad range of frequencies. This antenna is made of a series of dipoles placed along the antenna axis at different space intervals of time followed by a logarithmic function of frequency. The log-periodic antenna is used in a wide range of applications where variable bandwidth is required along with antenna gain and directivity.
A bow-tie antenna is also called a Biconical antenna or Butterfly antenna. Biconical antenna is an omnidirectional wide-band antenna. According to the size of this antenna, it has low- frequency response and as a high-pass filter. As the frequency goes to higher limits, away from the design frequency, the radiation pattern of the antenna gets distorted and stretch.
Most of the bow-tie antennas are indirect of biconical antennas. The discone is a type of half-biconical antenna. The bow-tie antenna is a planar, and consequently, directional antenna.
Log-Periodic Dipole Array
The element at the back end of the array is the high size with the half-wavelength operating in a low-frequency range. The spacing of the element gets reduced towards the front end of the array wherein the smallest arrays are placed. During this operation, as the frequency varies, a smooth transitional takes place along the array of the elements, which leads to forming an active field. The most common type of antenna used in wireless communication technology is a log-periodic dipole array fundamentally build a number of dipole elements. These dipole-array antennas shorten in size from the back end to the front end. The leading beam of this RF antenna comes from the lesser front end.
A log–periodic antenna, also called a log-periodic array or log-periodic aerial, is a multi-element, directional antenna designed to operate over a broadband of frequencies.
A class of directional antennas, Aperture Antennas have an opening in the surface. Usually, the aperture antenna consists of Dipole or Loop Antenna in a guiding structure with an opening to emit radio waves.
Slot antennas are used generally at frequencies between 300 MHz and 24 GHz. The slot antenna is popular because there can be cut out of whatsoever area they are to be mounted on and have radiation patterns that are pretty omnidirectional (similar to a linear wire antenna). The polarization of the slot antenna is linear. The slot size, shape and what is behind it offer design variables that can be used to tune performance.
A horn antenna is applied to the transmission and reception of microwave signals. It derives it the characteristic labile appearance. The labile portion can be square, rectangular/conical. The maximum radiation and response correspond with the axis of the horn. In this importance, the antenna resembles an acoustic horn. It is usually maintained with a waveguide.
A horn antenna must be a definite minimum size relative to the wavelength of the incoming or outgoing electromagnetic field. If the horn is too small or the wavelength is too large and the frequency is too low, the antenna will not work efficiently.
Horn antennas are generally used as the active element in a dish antenna. The horn is pointed to the center of the dish reflector. The use of a horn, more than a dipole antenna or any other type of antenna, at the focal point of the dish, minimizes loss of energy around the edges of the dish reflector. It also minimizes the response of the antenna to unwanted signals not in the favored way of the dish.
Horn antennas are used all by themselves in short-range radar systems/measuring device, especially those used by law-enforcement personnel to measure the speeds of approaching or retreating vehicles.
Microstrip antennas have become fashionable in some wireless communications systems, such as in the use of arrays with parabolic reflectors or even in the use of a patch antenna in the back of a cellular phone.
Rectangular Microstrip Patch Antenna
A patch antenna is a type of radio antenna, which can be mounted on a flat surface. It consists of a flat rectangular sheet or patch of metal, mounted over a higher sheet of metal called a ground plane.
Quarter-Wave Patch Antenna
A small quarter-wave rectangular microstrip patch antenna with the impedance bandwidth of 35% was constructed for the frequency of about 2 GHz. The antenna has a probe feed with an integrated capacitor to recompense for the probe inductance and produce a dual-resonant shape. The radiation pattern of the raised antenna is fairly omnidirectional and the polarization breakage is low, so it is fitting for certain applications in mobile communications.
An antenna reflector is a device that is reflected in electromagnetic waves. Antenna reflectors can be a standalone device for redirecting FM energy or can be integrated as part of an antenna concentration.
Flat-plate Reflector Antenna
The figure depicts a plane reflector antenna type. It consists of a primary antenna and reflecting surface. With this arrangement, it is useful to radiate EM energy in the desired direction but not possible to collimate energy in forwarding direction.
Following parameters depend on the position of primary antenna and its polarization in the plane reflector antenna:
• Radiation Pattern
Corner Reflector Antenna
The figure depicts corner reflector antenna type. It consists of two or three mutually intersecting conducting flat surfaces. In this type, the feed element can be either dipole or an array of collinear dipoles. The dihedral form is most popular in this type of antenna reflector. Trihedral forms with mutually perpendicular surfaces are used for the radar target application.
The corner reflector antenna type is used to achieve collimation of EM energy in forwarding direction. It is used to suppress radiation in the backward and in the side directions.
Parabolic Reflector Antenna
The figure depicts a parabolic reflector antenna. This type of antenna has a shape of paraboloid and hence it has properties of a parabola. The various feed antennas are used at the focal point. The figure shows the horn antenna at the feed point.
Let us understand the operation of the parabolic reflector antenna. As shown waves generated by horn antenna are incident on the reflector. The radiation is concentrated along the parabola axis. The waves are canceled in other directions due to the path as well as phase differences. This way parabolic reflector antenna converts spherical wave into a plane wave.
The parabolic reflector is further categorized into the following types based on the reflector plate:
1.Parabolic cylinder reflector
2. Cut or truncated parabolic reflector
3. Pillbox or cheese antenna reflector
4. Torus antenna reflector
5. Offset parabolic reflector antenna.
Feeding for this types of reflector antennas is done using any of the following given below :
• Half-wave Dipole
• The array of collinear dipoles
• Yagi-Uda antenna
• Horn antenna
• Cassegrain feed
Advantages: Small size and low cost.
Disadvantages: The presence of side lobes here create EMI. The effect of EMI is more dominant in low noise receivers due to imperfections in the reflector. This is the disadvantages of this type of antenna.
The antennas, which we have discussed till now, used the plane surface. The lens antennas used the curved surface for both transmission and reception. Lens antennas are made up of glass, where the converging and diverging properties of the lens are followed. The lens antennas are used for high-frequency applications.
The frequency range of usage of lens antenna starts at 1000 MHz but its use is greater at 3000 MHz and Over.
To have a better understanding of the lens antenna, the working principle of a lens has to be known. A normal glass lens works on the principle of refraction.
In radio and telecommunication, a traveling-wave antenna is an antenna that uses a traveling wave on the main radiating mechanism. Their separate feature is that the radio-frequency current that generates the radio waves travels through the antenna in one direction. This is in contrast to a resonant antenna, such as the monopole or dipole, in which the antenna acts as a resonator, with radio currents traveling in both directions, bouncing back and 4th between the ends of the antenna. The advantage of traveling wave antennas is that as there are nonresonant they once and again have a wider-bandwidth than resonant antennas. Common types of traveling wave antenna are—
- The Beverage antenna and
- The rhombic antenna.
Long Wire Antenna
The long wire antennas are using a number of dipoles. The length of the wire in these types of antennas is n times λ/2
$$L = n \ \lambda/2$$
- λ is the wavelength,
- L is the length of the antenna,
- n is the number of elements
As “n” increases, the directional properties also increase.
Types of Long-wire Antennas
Long wire antennas are separated into two types of antennas namely − Resonant Antennas and Non-resonant Antennas.
The Yagi antenna, also Called a Yagi-Uda array, The Yagi antenna is a directional antenna commonly used in communications when a frequency is above 10 MHz. This type of antenna is popular within Amateur Radio and Citizens Band radio operators. It is used at satellite communications systems.
Helical Wire Antenna
A helical antenna is a specialized antenna that is discussed as a hybrid of the radiating elements — loop antennas and the dipole. The conducting wire is wound in the form of a helix. The antenna, in most cases, is mounted over a ground plane with a feed line connected between the ground plane and the bottom of the helix. As it is a traveling wave antenna, the current and phase vary continuously along with the helical antenna. Because of their identical and special properties, helical antennas are widely used in simple and practical applications such as in radios and satellite communications.
Spiral antennas belong to the class of frequency-independent antennas, the antennas are characterized as having a very high bandwidth. The fraction bandwidth can be as high as 30:1. This means that if the lower frequency is 1 GHz, the antenna would still be efficient at 30 GHz, and every frequency in between.
An antenna array is a radiating system, which consists of individual radiators and elements. Each of this radiator, while functioning has its own induction field. The elements are placed so closely that each one lies in the neighboring one’s induction field. Therefore, the radiation pattern produced by them would be the vector sum of the individual ones. shows the following image another example of an antenna array.
Two-Element Array Antenna
We start by deriving the far-field radiation pattern for the case of the easy array, two isotropic point source elements divided by a distance d, as shown in Figure above. The net-far-field in the direction is given as
where , is the wavenumber and is the inherent phase difference between the two sources. and are the amplitudes of the electric field the two sources, at the faraway point under consideration. The reference point for the phase, referred to as the phase center, is taken half-way between the two elements. If the two sources have equal strength, and we have
Linear Array Antenna
An antenna array is of multiple connected antennas which work a single antenna, to transmit/receive radio frequency waves. The individual antennas are usually connected to a single receiver/transmitter by feedlines that feed the power to the elements in a specific phase relationship. The radio waves dispersed separate antenna combine and superpose, adding together to improve the power radiated in intentional directions, and canceling to reduce the power radiated in other directions. Similarly, when used for receiving, the separate radio frequency currents from the individual antennas join in the receiver with the correct phase relationship to increase signals received from the desired directions and cancel signals from undesired directions. More improper array antennas may have multiple transmitter/receiver modules, each connected to a separate antenna element.
Phased Array Antennas
An array of antennas in which all of the phases of each signal that feeds every antenna are set in like as a way that the effective radiation pattern of the whole array is set toward the desired direction and that the signals be produced toward undesired directions are suppressed. It is a way to direct waves of radiation toward the aimed direction.
A phased array is also called a phased antenna system.
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