Communication Engineering Chapter.5.pptx

Communication Engineering Chapter 5

1. Communication Engineering Ch.5 Antenna and Wave Propagation

2. EM spectrum and Application

3. Applications Radio waves - radio and television Microwaves - satellite communications and cooking food Infrared - Electrical heaters, cooking food and infrared cameras Visible light - Fibre optic communications Ultraviolet - Energy efficient lamps, sun tanning X-rays - Medical imaging and treatments Gamma rays - Medical imaging and treatments

4. Concept of Antenna An antenna is structure capable of radiating or receiving electromagnetic waves, function is to couple the transmitter or receiver to space. An Antenna is a transducer, which converts electrical power into electromagnetic waves and vice versa. An Antenna can be used either as a  transmitting antenna  or a  receiving antenna . In the field of communication systems, whenever the need for wireless communication arises, there occurs the necessity of an antenna.  Antenna  has the capability of sending or receiving the electromagnetic waves for the sake of communication.

5. Radiation of wave and Radiation pattern Antenna radiation patterns These patterns are a function of the direction of departure of the electromagnetic wave and can represent quantities such as gain, directivity, electric field, or radiation vector. Antenna performance is often described using its principal E- and H-plane patterns.  Surface-wave radiation patterns These patterns depend on the source process, the depth of the earthquake, and the frequency of the seismic waves.  Here are some other things to know about radiation and waves:  Electromagnetic radiation is classified by wavelength into radio wave, microwave, infrared, visible light, ultraviolet, X-rays, and gamma rays.  Much of modern technology is based on electromagnetic radiation, including radio waves from a mobile phone, X-rays used by dentists, and the energy used to cook food in a microwave.  Scientists discovered much of what we know about the structure of the atom by observing the interaction of atoms with various forms of radiant energy. 

6. Isotropic Antenna An isotropic antenna is a theoretical antenna that radiates power equally in all directions. It's also known as an omni directional antenna.  Isotropic antennas are used as a reference point to compare different types of antennas and calculate quantities like antenna gain and effective radiated power (ERP). The directional ability of a real antenna is measured by comparing its maximum radiation to that of an isotropic source. This is usually expressed in decibels over isotropic ( dBi ).  Isotropic antenna Real antenna Radiation Radiates equally in all directions Radiates stronger in some directions than in others In reality, no physical isotropic antenna exists. Normal antennas maximize radiation in one direction while minimizing it in other directions.

7. Polarization Horizontal and vertical polarization are two types of linear polarization that describe the orientation of an antenna's electrical field in relation to the Earth's surface:  Horizontal polarization The electrical field moves sideways in a horizontal plane, parallel to the Earth's surface.  Vertical polarization The electrical field oscillates up and down in a vertical plane, perpendicular to the Earth's surface.  Polarization is important when choosing an antenna because both antennas need to have matching polarizations for efficient communication. Horizontally polarized antennas have difficulty communicating with vertically polarized signals.  A third type of polarization is slant polarization, which occurs when the electrical field oscillates at a 45-degree angle to a reference plane. 

8. EM waves

9. Directivity and Gain of Antenna Directivity Antenna directivity is a measurement of how well an antenna focuses its radiation in a specific direction. It's the ratio of the radiation intensity in a particular direction to the average radiation intensity across all directions Gain The gain of an antenna in a given direction is defined as the ratio of the intensity, in a given direction, and the radiation intensity that would be obtained if the power accepted by the antenna were radiated isotropically . This is called the absolute gain.

10. Dipole Antenna Dipole Antenna : Working & Its Applications The antenna is a communication, used to transmit & receive signals to represent some information. The first antenna was invented by Germans in the year 1888 and used for  wireless communication  purposes. These antennas can broadcast both microwave & radio signals. There are different  types of antennas  available that are classified based on their application like wire, log periodic, aperture, microchip, reflector, lens, array, and traveling wave. So knowing each antenna and its purpose is mandatory to use in suitable applications. For that, this article discusses an overview of one of the types of wire antenna namely  dipole antenna , and its working with applications. What is Dipole Antenna? A dipole antenna is a type of RF antenna that includes two conductive elements like wires or rods where the metal wire length is half of the highest wavelength approximately in free space at the operation of frequency. At the center of the antenna, the conductive materials are separated through an insulator which is called an antenna section. The dipole antenna diagram is shown below. Dipole Antenna  The RF voltage source is given to the middle of the antenna then the voltage & current supplying throughout the two conductive elements generate an electromagnetic or radio signal and this signal is radiated outside of the antenna. At the center of this antenna, the voltage is minimum and current is maximum whereas the voltage is maximum & current is minimum at the dipole antenna two ends. Dipole Antenna Design A dipole antenna includes two conductive elements like wires and rods or wires where the feeder at the center & radiating sections of the antenna are on either side. The metal wires’ length is half of the highest wavelength that is λ/2 within free space at the frequency of operation. The basic  dipole antenna diagram  with the center feed point is shown below. Dipole Antenna Circuit Diagram.The conductive element in the antenna is split in the middle into two sections through an insulator which is called an antenna section. These sections are simply connected to a coaxial cable or feeder at the middle of the antenna. We know that wavelength is the distance among two consecutive highest or lowest points. Here, the radiating element length can be determined by several properties of the antenna-like center operating frequency, feed impedance, etc. In this antenna, the length of the dipole is a significant parameter. Any type of antenna will work for either transmitting or receiving. In various wireless applications, the antenna can be activated in between the transmitter & receiver.

11. Once the RF voltage source is applied to the center of the two sections in the antenna then the flow of voltage & current throughout the two conductive elements can generate an electromagnetic or radio wave signal to be radiated outside of the antenna. At the center of this antenna, the voltage is minimum and the current is maximum. In opposition, the current is minimum & the voltage is maximum at the antenna’s ends. This is the current distribution of dipole antenna. The dipole antenna radiation pattern diagram is shown below which is vertical to the axis of the antenna. The radiation pattern is the graphical depiction of the antenna’s radiation properties. The antenna’s radiation pattern will describe how the antenna will emit energy into space. Radiation Pattern

12. Parabolic reflector Antenna Parabolic Reflector Antennas: In parabolic Reflector antennas, parallel beam is generated when the reflector reflects the signals originating from the source positioned at the focus of a parabolic reflector .The main aim of parabolic reflector antenna is to transform the curved wave into the parallel wave front originated from the focus of the parabolic reflector It is directional antenna used at microwave frequency.

13. Micro strip Antenna One of the most useful antennas at microwave frequencies (f > 1 GHz). It usually consists of a metal “patch” on top of a grounded dielectric substrate. The patch may be in a variety of shapes, but rectangular and circular are the most common. Low profile (can even be “conformal,” i.e. flexible to conform to a surface). Easy to fabricate (use etching and photolithography). Easy to feed (coaxial cable, microstrip line, etc.). Easy to incorporate with other microstrip circuit elements and integrate into systems. Patterns are somewhat hemispherical, with a moderate directivity (about 6-8 dB is typical). Easy to use in an array to increase the directivity. It is used in satellite communication, microwave communication, mobile antennas, GPS antenna.

14. Base Station Antenna ,Mobile Station Antenna Base Station is the basic unit between the mobile switching center and the users. In the last two decades there is an immense growth in the world of mobile communications. The technology has been upgraded from the GSM to the 2G\3G\4G and LTE (Long Term Evolution). With this, the antennas for the base stations are also getting advanced day by day. Various types of geometries have been designed for the base station applications like Micro strip Patch antennas , slot antenna, dipole antenna , stacked patch antennas etc. Antenna arrays have also been designed for the better results and performance of the antenna. The various types of antenna and their results are compared here. The most used antenna for the Base stations are dipole antenna

15. Smart Antenna need and applications A smart antenna is an advanced antenna that uses signal processing algorithms to improve the performance of wireless communication systems. Smart antennas are used in mobile communication systems to:  Improve signal quality Smart antennas can focus transmitted energy towards a specific receiver, while reducing energy transmitted in other directions.  Increase capacity Smart antennas can increase the signal coverage distance and improve the transmission rate.  Reduce interference Smart antennas can synthesize nulls to suppress interference from other directions.  Smart antennas are also known as adaptive array antennas, digital antenna arrays, and MIMO. They are used in various wireless communication systems, including cellular networks, Wi-Fi networks, satellite communication, and radar systems. 

16. Space wave propagation Radio wave propagation is the way radio waves behave during their transfer from one point to another on Earth through various layers of the atmosphere. They are the most used waves in the electromagnetic spectrum. They are used in a variety of frequencies and wavelengths for communication like Ground Wave propagation, Sky Wave propagation and Space wave propagation. Space wave propagation is the propagation of radio waves within the troposphere region of the atmosphere,i.e . 20km above the ground level. In this article, we will learn in detail about space wave propagation, its components, advantages, disadvantages, factors affecting space wave propagation and its applications. Space Wave Propagation Space wave propagation is the transmission of radio waves directly from the transmitter to the receiver through the troposphere region of the atmosphere. It is a type of line of sight communication. It allows for transmission of the waves using a high frequency. These waves can travel in the troposphere region which is almost 20km above ground level. Thus most of the space wave propagation occurs in the troposphere layers. They are also known as tropospheric communication. Since these waves propagate like any other electromagnetic wave in free space, they are called space waves. Space Wave Propagation Diagram The image below is a diagrammatic representation of the propagation of the space wave. As seen in the image, the space wave follows a direct path between the transmitter and the receiver or follows the path where the troposphere layers are involved. This direct path most of the time falls in the troposphere region of the atmosphere. Space Wave Propagation Frequency Range Space waves propagate in the frequency range of 30 MHz to 300 MHz, which is considered as ultra high frequency (UHF) bands. Due to their high frequency, they have less wavelength thus they cannot be transmitted to long distances restricting them to the line of sight characteristics. Their high frequency allows these waves to carry more energy. Factors Affecting Space Wave Propagation Propagation of space waves are subjected to factors like Height of the receiving and transmitting antennas. For improved range, the antennas should be high but making too high antennas have its own set of limitations. The curvature of the Earth is also an important factor governing space wave propagation. The distance between the antennas determines the type of space wave propagation. The presence of obstacles in the path of the waves results in the loss of energy of the waves.

17. Space wave propagation

18. Components of Space Wave Propagation The different components of Space Wave Propagation are the following: Direct Waves-   These waves are propagated directly between the transmitting and the receiving antenna. Reflected Waves-  Some waves reach the receiver after getting reflected by the ground. Tropospheric Waves-  These types of waves traverse through the troposphere of the Earth to reach the receiver.

19. Application of Space Wave Propagation Space wave propagation has different applications such as Line of sight communication Television broadcast Radar communication including both general communication by radio waves or transmission at specific channels and frequencies Microwave linking or the transmission of radio waves in the microwave frequencies to transmit videos, audios, etc.

20. Duct propagation Duct propagation is a phenomenon that occurs when electromagnetic radiation, such as radio waves, bends back to the Earth's surface due to atmospheric reflection. This happens when the atmospheric refractivity decreases rapidly with increasing altitude.  Duct propagation is most common in the lower layer of the Earth's atmosphere, around 50 meters above the troposphere. In this region, higher frequency waves, such as microwaves, UHF, and VHF, refract back into the atmosphere instead of reflecting off into the ionosphere.  Duct propagation can affect communication and radar equipment at sea, causing: Large differences in radar ranging, angle measurement, and speed measurement Enhanced radar clutter Large-area detection blind spots  Duct formation is associated with temperature inversions and sharp decreases in humidity with height. 

21. Ground wave propagation Ground wave propagation is a type of radio wave propagation that occurs when radio waves travel along the surface of the Earth, from a transmitting antenna to a receiving antenna. It's also known as a surface wave.  Ground wave propagation is used for short-distance communication, such as: Local radio broadcasting, Radar, Amateur radio communications, and Radio navigation.  Ground wave propagation is important for radio signals below 30 MHz, but is generally insignificant at higher frequencies.  Factors that affect ground wave propagation include: Ground conductivity, Topography, Dielectric constant, Soil type, and Moisture content.  The range of ground wave propagation depends on frequency and ground conductivity. Lower frequencies and higher ground conductivity permit longer distances. 

22. Troposphere scattered propagation Tropospheric scatter , also known as  troposcatter , is a method of communicating with  microwave radio  signals over considerable distances – often up to 500 kilometres (310 mi) and further depending on frequency of operation, equipment type, terrain, and climate factors. This method of propagation uses the tropospheric scatter phenomenon, where radio waves at  UHF  and  SHF   frequencies  are randomly scattered as they pass through the upper layers of the  troposphere . Radio signals are transmitted in a narrow beam aimed just above the horizon in the direction of the receiver station. As the signals pass through the troposphere, some of the energy is scattered back toward the Earth, allowing the receiver station to pick up the signal. Normally, signals in the microwave frequency range travel in straight lines, and so are limited to  line-of-sight  applications, in which the receiver can be 'seen' by the transmitter. Communication distances are limited by the  visual horizon  to around 48–64 kilometres (30–40 mi). Troposcatter allows microwave communication beyond the horizon. It was developed in the 1950s and used for military communications until  communications satellites  largely replaced it in the 1970s. Because the troposphere is turbulent and has a high proportion of moisture, the tropospheric scatter radio signals are  refracted  and consequently only a tiny proportion of the transmitted radio energy is collected by the receiving antennas. Frequencies of transmission around 2 GHz are best suited for tropospheric scatter systems as at this frequency the wavelength of the signal interacts well with the moist, turbulent areas of the troposphere, improving  signal-to-noise ratios .