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1. 1. Research 01 (P2.1, M1, D1) 1.1 Introduction to Electromagnetic First I would like explain what a wave is. Wave is a disturbance or oscillation that travels through space time, accompanied by a transfer of energy. Wave motion transfers energy from one point to another, often with no permanent displacement of the particles of the medium. Basically waves can be divided into two categories. Longitudinal and transverse categories behave in two different ways in moving and oscillating. Longitudinal waves oscillating parallel way with its energy travel; slinky is an example for longitudinal waves. But transverse waves are oscillated perpendicular to its energy flowing direction; water ripples is an example for this type. Mechanical and Electromagnetic are two main types of waves. Mechanical Wave needs a medium to be travelled and Electromagnetic Waves do not want any medium to travel. Mechanical wave may be longitudinal or transverse while Electromagnetic wave is just transverse. Electromagnetic wave is a creation of mixing, binding electrical field and a magnetic field together. In 1873, Scottish scientist James Clerk Maxwell unified the theories of electricity and magnetism, and eloquently represented their relations through a set of profound equations best known as “Maxwell’s equations”. Maxwell said, if electricity flows through a conductor, magnetic field is generated around that conductor perpendicular to direction of electricity flows. To find the direction of magnetic field Fleming’s right hand law can be utilized. So, Electrical field and magnetic field is always perpendicular each other in electromagnetic waves to the direction of flowing. Electromagnetic wave has some properties such as polarity and electromagnetic energy. Polarization is a measurement of the electromagnetic field alignment. There are three main properties of electromagnetic waves as frequency, wavelength and velocity.
2. 2. Current direction (Towards the paper) Magnetic field (clockwise direction) Figure 01: Fleming’s right hand law indicating. This diagram shows that electrical field is always perpendicular to magnetic field. Electromagnetic waves have different wave lengths. Figure 02 : electromagnetic wave directions [1]
3. 3. Figure 03: wave length of a wave. Wave length is 360 degree (one cycle) change of wave (in phase). Wave length is one parameter to measure a considered wave. Another parameter was found by Heinrich Hertz, a German physicist as cycles per one second. Electromagnetic waves have different wave lengths and frequencies. Because of that, Electromagnetic spectrum was introduced. Figure 04: Electromagnetic spectrum with its sizes.[2]
4. 4. Electromagnetic spectrum consist different waves with different wave lengths and frequencies. Radio, micro, infrared (I.R), Visible light, U.V, X rays and Gamma are represent areas of this spectrum. These entire wave has speed of light (3 in free space approximately and that means no need of media to flow. Additionally, power level (amplitude) of electromagnetic wave is also considered. It needs high amplitude to transmit far distance. Furthermore considering, phase angle, gain, attenuation can be taken as properties of an electromagnetic wave. According to properties, different kind of electromagnetic waves are included in electromagnetic spectrum. Radio Waves According to definition of Radio frequency in a Wireless LAN, High Frequencies (300 kHz – 300 GHz) electromagnetic waveforms that are passed along a copper conductor and then radiated into the air via an antenna Radio wave is the first area of electromagnetic spectrum. Radio waves have lowest frequency and highest wavelength. Radio wave area can be divided again into certain frequency levels. Below chart indicates those different areas frequencies, wavelengths and their applications. According to graph of Frequency Band Wave length Applications 3- 30 KHz VLF 100 – 10 Km Sonar, fax, Navigation 30 – 300 KHz LF 10 – 1 Km Navigation 0.3 – 3 MHz MF 1 – 0.1 Km AM Broadcasting 3 – 30 MHz HF 100 – 10 m T. phones, fax, CB 30 – 300 MHz VHF 10 -1 m TV, FM Broadcasting 0.3 – 3 GHz UHF 1 – 0.1 m TV, mobile , radar 3 – 30 GHz SHF 100 – 10 mm Radar, satellite, microwave links 30 – 300 GHz EHF 10 – 1 mm Radar, wireless communication 0.3 – 3 THz THF 1 – 0.1 mm THZ imaging Figure 5: EM spectrum and applications
5. 5. Microwave Microwave is the next class of electromagnetic spectrum. This class has higher frequencies and lower bandwidths compared to radio waves. There is an interference region in both radio and microwave classes. Above mentioned SHF (Super High Frequency) and EHF (Extremely High Frequency) in that region. Because of higher frequency, attenuation is higher there. So can’t travel over large distances without broadcasting/ distributing centers in near distances compared to radio broadcasting centers (mobile phone towers). Microwave waves carry higher energy (eV) compared to radio waves. Microwaves are utilized for mobile communication, Radar communication. In mobile communication, microwaves are very important. Because of low wavelength very small antennas are needed. As well as this wave is used at microwave ovens because of higher energy of these waves. Infrared Infrared class has better frequency than microwaves. IR is the abbreviation for Infrared. Terahertz region is between microwave and infrared classes. Most times, Infrared waves transfer energy as Heat. Infrared is divided into three parts.  Far infrared: 300GHz – 30 THz (1mm – 10um).  Mid infrared: 30THz – 120 THz (10um – 2.5um).  Near infrared: 120THz – 400THz (10um - 750 nm). Infrared is used at remote controllers, night vision cameras, weather forecasting. Night vision cameras are mostly used in military operations, because it indicates temperature differences by different colors even in dark. Night mode options of usual cameras are operated by Infrared technology. Usually Infrared is considered as it is flowing heat. In night vision cameras, infrared is indicating live things from others, because temperature of blood is identified by infrared.
6. 6. Figure 08 : Photo of a IR camera http://www.x20.org/thermal/ Light This is the most important class, which associated with human eyes. Some other animal can see other classes such as IR, UV also. Although, Human been only can see in this light region. Electromagnetic radiation with a wavelength between 380 nm and 760 nm (790–400 terahertz) is detected by the human eye and perceived as visible light. Our main Light source, sun sends various kinds of waves although visible light can see us. Visible light can be produced by using Laser, which is used in compact disks, DVD,CD players and some printers. Visible light is a mixture of some wave frequencies. Different colors have different frequencies and wavelengths. Ultraviolet Ultraviolet is the next class of electromagnetic spectrum. UV is the abbreviation for ultraviolet. Upper region of UV is more close to light properties. Sun provide UV rays. UV use to destroy microbes. UV used to clean surgery devices also. UV lamp is a one made of UV, which do two duties. Provide purple color and attract insects are them. UV rays are not good for our skin specially, eyes.
7. 7. X – Rays X rays have giant energy. Stars emit X rays. upper ranges of UV are also ionized. Because of very short wavelength and higher energy X rays can go through many particles. Because of that X rays mainly utilized at medical science to view inside body. Detecting to X rays long time cause cancers. As well as X rays are used in security also. Airport bag and passenger checker is one example. Gamma Rays Gamma rays discovered by Paul Villard in 1900. These conduct protons with giant energy. Gamma rays have very small wavelength and can go through many items. Gamma rays given off by stars and radioactive substances. Gamma rays are utilized to destroy unwanted cancer cells, which called as radiotherapy. Gamma rays are also used for the irradiation of food and seed for sterilization. 1.2 Definition for Antenna An antenna is a device, which is involved in signal broadcasting. According to Webster’s dictionary, Antenna is defined as “a usually metallic device (as a rod or wire) for radiating or receiving radio waves.” According to the IEEE standard the antenna or Arial as” a means for radiating or receiving radio waves.” In other words, the antenna is a transitional structure between free space and a guiding device. Usually, Antenna is an isolated device. It associates with Source/ receiver, Transmission line also. According to Yi Huang, Kevin Boyle (2008), Antenna is a device which can radiate and receive electromagnetic energy in an efficient and desired manner. If antenna is transmitting antenna, it consist a source (voltage). Receiver is replaced source if that is a receiving antenna. Antenna use voltage and
8. 8. current and produce electromagnetic wave in transmission antenna. In receiving side opposite tsk is happened. [3] History of antenna According to historical reviews, first incident associates with antennas is belongs to Michel Faraday. He had sent a key to sky by using a kite working as an antenna. However, the history of antennas dates back to James Clerk Maxwell who unified the theories of electricity and magnetism and their relationships. In 1873, he proved that light is electromagnetic and both light and electromagnetic waves travel by wave disturbances of the same speed. In 1886, Professor Heinrich Rudolph Hertz demonstrated the first wireless electromagnetic system. He utilized a variable voltage source, two conducting balls and a dipole ( piece if wire) to check sparks occurring at both transmitter side and receiver side.He was able to produce in his laboratory at a wavelength of 4m a spark in the gap of transmitting half of wavelength ( dipole which, was then detected as a spark in the gap of a nearby loop. That was the first practical implementation of broadcasting. In 1901, Guglielmo Marconi was able to send signal over long area from Poldhu in Cornwall to St. John’s Newfoundland in Canada. That transmitting antenna consisted of fifty vertical wires in the form of a fan connected to ground through a spark transmitter. By 1940, radio frequency transmission was further developed UHF (Ultra high frequency). A contributing factor to this new era was the invention of microwave sources with 1 GHz and above frequencies. In this time most of antenna elements were wire made such as long wires, dipoles, rhombuses, fans, helices etc.. And they were used either as single elements or in arrays. Later, some new concepts were invented to develop and increase radiation of antenna as whole antennas (open ended wave guides, slots, horns, lenses, reflectors) .These antennas were used in advanced utilizations like radar, deep space projects, and remote sensing projects by using microwaves region. Infinite bandwidth
9. 9. antennas did a great revolution in antenna history. These were called as “frequency independent”. These antennas were primarily used in the 10- 10,000 MHz region in a variety of applications including television, point to point communication, lenses etc…. 1.3 Basics of an Antenna Antennas basically can be divided into two main categories. Those are Transmitting antenna and Receiving antenna. As I mentioned before antenna is not an isolated device. Figure 06: Antenna as a transition node. [4]
10. 10. If consider about architecture of antenna it’s easy to demonstrate that using thevenin equivalent circuit as below. Figure 07: Thevenin equivalent for an antenna system Here voltage source is replaced by an ideal generator and the transmission line is represented by a line with characteristic impedance ( while antenna is represented by a load when, ( . The load resistance is representing the conduction and dielectric losses associated with the antenna system. is called as radiation resistance which, is used to demonstrate radiation occur by antenna. Is the reactance part which, is utilized to represent the imaginary part of the impedance associated with the radiation by antenna. If antenna is ideal, magnitude of must be zero. That means the energy generated by source should be totally converted to (for radiation). Consist with both real and imaginary parts such as a complex number. This reveals us that electromagnetic waves behave in two planes. The losses due to the line, antenna and the standing waves are badly affect on transmission process. These losses can be reduced by low loss lines (by minimize ). The standing waves can be reduced and the energy storage of the line could be minimized by matching load impedance of the antenna to the characteristic impedance of the line.
11. 11. Radiation mechanism of an antenna If consider about radiation mechanism, antenna responsible for distributing waves or collecting waves. Let us consider how this is happening. In transmitting antennas, for pull the wave from antenna, high frequency with high power is needed. For this purpose, higher frequencies with high power supply to the transmitting antenna. In transmitting antenna, current is converted into Electromagnetic field. This is discussed above with Maxwell’s law. When current is travelling through conductor, magnetic field is induced around that conductor. Magnetic field is varying according to rate of change of charge (electrons) flowing. For obtain higher frequency, modulation concept is utilized. Voltage is obtained by electrical field and current is obtained by magnetic field. When magnetic field is varying current is induced in that circuit according to Faraday’s law Process of transmitting antenna system is shown in figure 06. In simply saying, Transmitting antenna convert current and voltage into radio waves (electromagnetic), while receiving antennas gather electromagnetic waves. Transmission Line As mentioned above, antenna is not an isolated node. Transmission line is also there to connect signal generator or receiver with the antenna. In an antenna communication, transmission line must be suitable. If not phase distortions, energy losses, fading waves might be occurred. Even by transmission line type, purpose of antenna is varied. There are some types of transmission lines as,  Double wire (two wires).  Microstrip.  Coaxial.  Stripline.  Coplanar Waveguide. These types of antennas varied with their bandwidth, loss characteristic, characteristic impedance, radiation, etc.
12. 12. Two wire Below you can see a cross sectional view of two wire transmission line. Current are flowing opposite directions in these two wires. Figure no: 08 cross sectional view of two wire transmission line [5]http://www.rfcafe.com/references/electrical/transmission-lines.htm This is the most common transmission line type usually. Here, two separate wires are covered with another medium(electrical insulator). According to above diagram, each wire has diameter if d and length between two wires is D. If that cover has permittivity of Inductance (L) and capacitance(C) for unity length is given by, √ √ Usually the characteristic impedance ( Value is being varied in 270 to 310 Ωs. Main application is television antennas ( rabbit ear antennas).When current flowing in two directions in these two wires dielectric field is occurred around this transmission line and Radiation is occurred here at higher frequencies. Because of that these transmission lines have less efficiency when frequency is greater than 300MHz.
13. 13. The characteristic impedance of this transmission line is given by, √ √ Microstrip Figure no 09 : named cross sectional of Microstrip transmission line.[6]
14. 14. http://www.photond.com/products/fimmwave/fimmwave_applications_09.htm Microstip transmission line procedure is very familiar with two – wire system. Instead of two wires, there are two plates called as microstrip and ground plates are separated by dielectric (electrical insulator) plate (substrate according to above figure). By that radiation resistance can be reduced as well. Mainly, utilized in microwave components. If consider about electromagnetic distribution, majority of both electrical and magnetic field are flowing in the transverse plane. This might be hazardous sometimes if there is big current. Characteristic impedance of microstrip line is given by, √ When, √ d= thickness of substrate. W = width of strip. Conductor loss and dielectric substance loss are common errors / losses occurs in microstrip transmission lines. Coaxial
15. 15. Figure no 10: named cross sectional of coaxial cable.[7] http://www.phy.davidson.edu/stuhome/phstewart/IL/speed/cableinfo.html Coaxial cable is the most common transmission line in domain and household. This consist of tubal conductor is covered by another tubal conductor. These two conductors are separated by electrical insulator. This entire package is covered by another dielectric cover. Data is transmitted through the center wire, while the outer braided layer serves as a line to ground. Both of these conductors are parallel and share the same axis. As all electrical components, coaxial cables have characteristic impedance. This impedance depends on the dielectric material also. That is given by, √ √ ⁄ When, R = Diameter of outer conductor. r = Diameter of inner conductor (main conductor). Data transmission velocity of main conductor (v) is √ ⁄ when; c is the speed of light.
16. 16. Stripline Figure no 11 : cross sectional of stipline with dimensions.[8] This configuration is usually called as single stripline. Dual stripline configuration is the other configuration available. Stripline has bit differences compared to microstrip configuration. In microstrip, there are one conductor and one ground plate separated by dielectric plate. Here, there are two ground plates and one conductor separated each other with dielectric medium. Stripline filters and couplers always offer better bandwidth than their counterparts in a microstrip. Another advantage of the stripline is that fantastic isolation between adjacent traces can be achieved. Because of extra ground plate, stripline is harder and expensive than microstrip. As well Because of the second ground plane, the strip width is much narrower for given impedance and the board is thicker than that for a microstrip. Usually, characteristic impedance of stripline transmission line is being varied 50 to 75 ohms. That is given by, √ W = width of the conductor. t = thick of the conductor. d = length between two ground plates. A = [2 ( ( ( B = √⁄
17. 17. Coplanar waveguide Figure 11(a) : coplanar waveguide without ground cross sectional.[9] Figure 11(b) : coplanar waveguide with ground cross sectional. [9] Coplanar waveguide is very efficiency transmission line, which uses a ground conductor that is coplanar with the signal conductor. This structure is very similar to stripline configuration. In here conductor is always separated. So, it can keep constant impedance. This configuration can be used for high frequencies and has higher bandwidth also. There are two basic configurations as with ground and without ground.
18. 18. 1.4 Types of antennas By today, antennas are used in various fields in various ways. At there, different types of antennas are being used for different purposes. There are many types of antennas. Some of them are, Wire antennas These type antennas are the most common antennas in everywhere such as automobiles, buildings, ships, aircrafts, spacecraft and many other places. There are various shapes of wire antennas such as dipole, loop, and helix. Dipole Dipole is an antenna which is made of two conductors connected together. Half wave dipole, quarter wave dipole and folded dipoles are categories of dipole antennas. According to Yi Huang and Kevin Boyle (2008), Dipoles are one of the simplest but most widely used types of antenna. This is also called as Hertz’s antenna, because hertz used dipole for his inventions. In half wave dipole consist of two conductors which have quarter of wavelength in each conductor. Total length of antenna is half of wave length. Current is flowing in these conductors with association of voltage to radiate electromagnetic wave. Let us consider how that radiation happens. ⁄ ⁄ Current Voltage
19. 19. Figure 12: half wave dipole basic moment Here in this basic moment, current is maximum and voltage is minimum at the middle point. Because of low voltage and higher current, a low impedance point is created in middle point and gets the ability to detect electromagnetic waves as well because other two corners hard to detect electromagnetic waves. In odd harmonics can see same incident. Because of that these dipoles can detect even two or three harmonics of based frequency as well. Yagi- Uda antenna This is another famous wire type antenna, which used in VHF and UHF communication. This is same as dipole, but there are more elements to change directivity, radiation pattern and phase angle. These elements are called as reflector, director. According to Ian Poole (2003), “The basic antenna consists of a central boom with the elements mounted to it at right angles as shown. The antenna consists of the main driven element to which the feeder is connected, and parasitic elements either side. These parasitic elements are not directly connected to the feeder but operate by picking up and re-radiating power in such a phase that the directional properties of the antenna are altered. This is achieved having the phase of the current in the parasitic element or elements in such a phase that it reinforces the signal in a particular direction, or cancels it out. There are two main types of parasitic element: reflectors that reflect power back towards the driven element, and directors that increase the power levels in the direction of the directors. The properties of a parasitic element are determined by their spacing and their electrical length.”
20. 20. http://en.wikibooks.org/wiki/Communication_Systems/Antennas Aperture Antennas Aperture antenna is mainly used for projects at higher frequencies. There are some antennas, such as pyramid, conical or rectangular shape. According to Yi Huang and Kevin Boyle (2008) is another group of antennas that are not made of metal wires but plates to form certain. Configurations that radiate/receive EM energy in an efficient and desired manner,. These antennas are very useful in the aeronautics and space applications, because they can be very easily built on the skin of the object. In addition, these antennas are coated with a dielectric material to protect them from the harmful effects on the environment. Horn antenna is usually used as an antenna to the opening. Horn antenna is the easiest to work with microwave transmission. This is widely used as a feeding element for large parabolic antenna radio astronomy and communication are installed worldwide. Besides its usefulness as a feed reflectors and lenses, is a common element of the phased array and serve as a universal standard for measuring the calibration and other high-gain.Usually there are four types of electromagnetic
21. 21. horns in E plane and H-plane pyramid cornial. Figure 13 : E plane, H plane and pyramid configuration horn antenna.[10] Figure 14 : Conical horn configuration antenna [11]
22. 22. Microstrip Antennas Microstrip antennas consist of a metallic patch or patches on grounded substratum. The metallic patch may have one of several configurations. Among them circular and rectangular configurations are widely used, because of ease of analysis and fabrication and good radiation characteristics such as low cross polarization radiation and also very versatile in terms of resonant frequency, pattern, impedance and polarization. These antennas can be placed in many applications and places such as airplanes, satellites, vehicles, mobile phones, missiles and many other applications because of inexpensive, high performance, easy to handle, easy to place. Array antennas Array antennas depend on arrays. Specific radiation pattern requirements cannot be obtained or fulfilled by single antenna element, because single elements usually have relativity wide radiation patterns and low values of directivity. These reasons occur low efficiency of an antenna and have to use numbers of antennas to achieve considered results. To design antennas with large directivity electrical dimensions of the antenna must be higher. But, that’s not practically success, because, high cost, high power, mechanical problems, disabilities and space problems. An alternative way to achieve large directivities, without increasing the size of the individual elements, is to use multiple single elements to form an array. Array is a sampled version of a very large single element. In an array, the mechanical problems are overcome. Arrays are most versatile antenna type because of higher efficiency. These antennas are being used in many applications such as aerospace, earthbound and many others. Yagi- Uda array, aperture array, Microstrip arry and slotted-waveguide array are some array configurations available.
23. 23. Figure 15 : A Phased Array Antenna with Microstrip Radiating Elements.[12] Figure 16 : Basic geometry of a slotted waveguide antenna.[13]
24. 24. Lens Antennas Main reason of using lens antennas in focus divergent energy/ waves to appropriate direction to reduce spreading in undesirable directions. By properly shaping the geometrical configuration and choosing the appropriate material of the lenses and can transform various forms of divergent energy into plane waves. These antennas can be used in most of the applications related to higher frequencies. In telecommunication, Television broadcasting and even in satellite communication these kind of antennas are utilized. Figure 17 : Schematic representation of a phased antenna array beam shaping system[14]
25. 25. Reflector Antennas Reflector antennas are mainly used in long way transmission tasks. Sometimes, called as “Dish” antennas because of its shape. That distance might be outer space to earth or large geographical area. These antennas are made for spread EM waves to large area in considered target. Parabolic reflector and corner reflector are two types of reflector antennas. Dipole or Horn antenna is used as the feed or radiating element. Very large gain can be achieved by reflector antennas. But placement of the antenna must be correct, because these antennas beam width is compared low. According to Ian Poole (2003), Initially these antennas were only used for professional applications, especially radio astronomy or satellite communications. However, with the advent of satellite television these antennas are often seen on the sides of houses for reception of these broadcasts. The gain mainly depend on dimensions of the reflector. Feed Figure 18(a) : Parabolic reflector with front feed
26. 26. Figure 18(b) : parabolic reflector with cassegrain feed. Figure 18(c) : A corner reflector.
27. 27. 1.5 Antenna parameters Above we discussed various kinds of antennas. Performances of those antennas depend on some of parameters. These parameters need to specify for complete description of the antenna performance. Some of those Antenna parameters are,  Antenna Gain.  Radiation pattern.  Beam-width.  Bandwidth.  Polarization.  Directivity.  Efficiency. Radiation Pattern Radiation pattern is also called as antenna pattern. Radiation pattern is variation of power, which radiated by the antenna as a functional representation. According to C.A. Balanis (2005), This is defined as “ a mathematical function or a graphical representation of the radiation properties of the antenna as a function of space coordinates”. This is represented as a function of the directional coordinates. Radiation properties include power flux density, radiation density, field strength, directivity, polarization or phase. The radiation property of most concern is the two or three dimensional spatial distribution of radiated energy as a function of observer’s position along a path or surface of constant radius. In an antenna radiation pattern is shown by three dimensions (3D) . Those are,  Field pattern (in linear scale) represent a plot of the magnitude of the electric or magnetic field as a function of the angular space.  Power Pattern (in linear scale) represents a plot of the square of the magnitude of electric or magnetic field as a function of angular space.  Power Pattern (in decibels) represents the magnitude of the electric or magnetic field in decibels as a function of angular space.
28. 28. Figure 19 : coordinate system for antenna analysis [15] Radiation power density The quantity used to describe the power associated with an electromagnetic wave is the instantaneous poynting vector defined by ( ( (
29. 29. Radiation Intensity Radiation intensity in a given direction is defined as “the power radiated from an antenna per unit solid angle.” The radiation intensity is a far field parameter and it can be obtained by simply multiplying the radiation density by the square of the distance. This is given as, U : Radiation intensity. r : Radius. : Radiation density. The radiation intensity always related to the far zone electric field of an antenna. BeamWidth The beamwidth of pattern is defined as the angular separation between two identical points on opposite side of the pattern maximum. In an antenna pattern, there are number of beamwidths. Half power beamwidth (HPBW) is the most common beamwidth type. That is defined as “In a plane containing the direction of the maximum of a beam, the angle between two directions in which the radiation intensity of one half value of the beam.” The beamwidth of an antenna is a very important factor of merit and often is used as a tradeoff between it and the side lobe level; that is, as the beamwidth decreases, the side lobe increases and vice versa. In addition, the beamwidth of the antenna is also used to describe the resolution capabilities of an antenna to distinguish between two adjacent radiating sources or radar targets.
30. 30. Directivity Directivity is defined as “the ratio of the radiation intensity in a given direction from the antenna to the radiation intensity averaged over all directions. This shows how much efficiency has in a considered direction. The average radiation intensity is equal to the total power radiated by the antenna divided by 4 If the direction is not specified, the direction of maximum radiation intensity is implied.” It can be stated as follows. When, the direction is mentioned, it implies the direction of maximum radiation intensity is expressed as, When, D = directivity D max = Maximum directivity U = Radiation intensity. U max = Maximum radiation intensity. U0 = Radiation intensity of isotropic source. P rad = Total radiated power.
31. 31. Antenna Efficiency The total antenna efficiency is used to take into account losses at the input terminal and within the structure of antennas. Such losses may be occur due to below reasons.  Mismatching of impedances in transmission line and Antenna. Reflections and side waves occur due to this incident.  Conduction and dielectric losses ( ). This r is radiation impedance, which discussed in Basics in antennas. This total antenna efficiency can be formed as, ( ( | | . Voltage standing wave ratio = | | | |
32. 32. Antenna Gain Antenna gain is always related to directivity and it’s a measure that takes with efficiency of the antenna as well as its directional capabilities. Antenna gain is defined as “the ratio of the intensity, in a given direction, to the radiation intensity, that would be obtained if the power accepted by the antenna were radiated isotropic. The radiation intensity corresponding to the isotropic radiated power is equal to the power input by the antenna divided by 4 Gain is expressed as, Bandwidth The bandwidth of an antenna is defined as “the range of frequencies within which the performance of the antenna, with respect to some characteristic, conforms to an specified standard.” If consider a dipole, bandwidth is the range which can be detected by corner to corner of dipole. We know, electromagnetic wave has speed of light according to invention of Scottish scientist James Clerk Maxwell. So, we can assume detecting frequency by calculating length of entire dipole. For broadband antennas, the bandwidth is usually express as the ratio of the upper to lower frequencies of acceptable operation. Bandwidth ratio reveals the upper and lower frequencies of an antenna. As an example, 10: 1 bandwidth indicates that, the upper frequency is 10 times greater than lower frequency. This technique is differing at narrowband antennas. For narrowband antennas, the bandwidth is expressed as a percentage of the frequency difference over the center frequency of the bandwidth. Bandwidth of an antenna is depending on other parameters (gain, input impedance, pattern, polarization) as well. Bandwidth is controlled at center of many antennas. By today bandwidth of antennas have been increased giant. 40: 1 is an example for that type antenna.
33. 33. Polarization Antenna is designed sometimes to transmit or receive signals to or from only one or two considered directions. Because of that even polarization is differ from direction to direction. Polarization of an antenna in a given direction is defined as “the polarization of the wave radiated by the antenna.” When the direction is not stated, the polarization is taken to be the polarization in the direction, which has maximum gain. The polarization of a wave is defined using wave radiated by the antenna in considered direction. Polarization is categorized as linear, circular or elliptical. If the vector that describes the electrical field at a point in space as a function of time always directed along the line, that is linear polarized field. According to shape of electric field traces can identify category of polarization. The figure of the electric field is traced in a clockwise or counterclockwise sense. Clockwise rotation of the electric field vector is also designated as right hand polarization. while, counterclockwise is left hand polarization. In practical world, the axis of antenna’s main beam must be directed along the polar axis of the radiation sphere. The polarization of the wave radiated by the antenna can also be represented on Poincare sphere. [16]
34. 34. References/ Bibliography [1] http://www.geo.mtu.edu/rs/back/spectrum/. [2] [3] IEEE transactions on antennas and propagation, vols. AP-17, No.3, May 1969; AP-22, No. 1, January 1974 and AP-31, No.6, Part ii, November 1983. [4] http://www.google.lk/imgres?imgurl=http://denmasbroto.com/files/antenna-as-a- transition-device.PNG&imgrefurl=http://denmasbroto.com/cetak-13-antenna-basic- theory.html&usg=__XzFWWQi- SXiFbe5FwVEHB64muJw=&h=529&w=454&sz=62&hl=en&start=1&zoom=1&tbn id=lU3TLvs5v8QDnM:&tbnh=132&tbnw=113&ei=l7EBUJmrKIa2hQe_xpDyBw&p rev=/search%3Fq%3Dantenna%2Bas%2Ba%2Btransitional%2Bdevice%26um%3D1 %26hl%3Den%26safe%3Doff%26sa%3DN%26biw%3D1360%26bih%3D667%26tb m%3Disch&um=1&itbs=1 [10] http://www.radio-electronics.com/info/antennas/waveguide/waveguide- impedance-matching-iris-post.php [11]http://www.google.lk/imgres?imgurl=http://img.directindustry.com/images_di/ph oto-g/high-gain-feed-horn-antenna- 764325.jpg&imgrefurl=http://www.directindustry.com/prod/ets-lindgren/high-gain- feed-horn-antennas-35072-764325.html&usg=__LjnhuZIyvjGv8DcGeFt3O- udeT0=&h=572&w=647&sz=29&hl=en&start=58&zoom=1&tbnid=Od8u- 6USyYJ6tM:&tbnh=121&tbnw=137&ei=808CUPSYCMenhAfyvYH4Bw&prev=/se arch%3Fq%3Dconical%2Bhorn%2Bantenna%26start%3D40%26hl%3Den%26safe% 3Doff%26sa%3DN%26biw%3D1360%26bih%3D667%26tbm%3Disch&itbs=1 [12] http://www.google.lk/imgres?imgurl=http://www.radio- electronics.com/info/antennas/waveguide/waveguide-e-h-horn- antenna.gif&imgrefurl=http://www.radio- electronics.com/info/antennas/waveguide/waveguide-impedance-matching-iris- post.php&usg=__mstNd_jliVd41R0B- uclNfluvI0=&h=307&w=250&sz=3&hl=en&start=2&zoom=1&tbnid=-OqdybTwTc- dHM:&tbnh=117&tbnw=95&ei=5k4CUNP5H4i3hAfknvSXCA&prev=/search%3Fq %3De%2Bplane%2Bhorn%2Bantenna%26hl%3Den%26safe%3Doff%26biw%3D13 60%26bih%3D667%26tbm%3Disch&itbs=1
35. 35. [13]http://www.google.lk/imgres?imgurl=http://www.wtec.org/loyola/satcom/fh2_26. gif&imgrefurl=http://www.wtec.org/loyola/satcom/c2_s1b.htm&usg=__3uif0JppUpa 2j_09nUsL99YwK0k=&h=550&w=733&sz=29&hl=en&start=20&zoom=1&tbnid=k Lt_wt5W5a3VgM:&tbnh=106&tbnw=141&ei=YFICUPOEEai80QXU0421Bw&prev =/search%3Fq%3Darray%2Bantenna%26hl%3Den%26safe%3Doff%26biw%3D136 0%26bih%3D667%26tbm%3Disch&itbs=1 [14] http://www.antenna-theory.com/antennas/aperture/slottedWaveguide.php [15]http://www.google.lk/imgres?imgurl=http://www.aanda.org/articles/aa/full/2004/ 46/aa1435/img60.gif&imgrefurl=http://www.aanda.org/articles/aa/full/2004/46/aa143 5/aa1435.fig.html&usg=__E-PzQOeZTM0zmNR65xCf_- Q_1ss=&h=425&w=461&sz=18&hl=en&start=12&zoom=1&tbnid=KkEh8L7zQuH2 oM:&tbnh=118&tbnw=128&ei=zocCUNLvK4yBhQfmyaH- Bw&prev=/search%3Fq%3Dcoordinate%2Bsystem%2Bfor%2Bantenna%2Bplotting %26hl%3Den%26safe%3Doff%26biw%3D1360%26bih%3D667%26tbm%3Disch&i tbs=1 [16] C.A Balanis (1989), Advanced Engineering Electromagnetics, John Wiley & sons, New York.
36. 36. Research 02 (P2.2, M3) Electromagnetic wave is a combination of Electrical field and Magnetic field according to Maxwell’s law. Electromagnetic wave is a transverse wave. In transverse waves, Energy transmitting direction is perpendicular to wave oscillating direction. One characteristic of transverse wave is no need of medium to transmit. Even in vacuum it can be transmitted. Any Electromagnetic wave has same transmitting speed of speed of light (3 . There are Electromagnetic wave having different Wave lengths and frequencies. At the beginning Light was the only one thing, which found in electromagnetic spectrum. 1n 1800, William Herschel found infrared light. He could find out the temperature of different colors by moving a thermometer through light split by a prism. In 1801 Johann Ritter invented that there are chemical rays as visible violet rays. This is called as Ultra violet rays. Light was named as an electromagnetic wave after 1845. In 1845, Michel Faraday invented that, light is a one type of electromagnetic. In 1895, Wilhelm Rontgen invented X rays, which can go through even human body. V = Velocity of transmitting wave. . = Wave length (2 .
37. 37. Figure 01 : Electromagnetic spectrum http://www.colourtherapyhealing.com/colour/electromagnetic_spectrum.php
38. 38. In electromagnetic waves as mentioned above, velocity is a constant value. So, frequency is inversely proportional to wave length. By considering above characteristics Electromagnetic wave spectrum has been created. Electromagnetic spectrum is classified into classes as,  Radio wave.  Microwave.  Infared.  Visible light.  Ultraviolet.  X – Ray.  Gamma.
39. 39. Figure 02 : Electromagnetic waves classes and wave lengths of them http://lasp.colorado.edu/cassini/education/Electromagnetic%20Spectrum.htm
40. 40. Radio Frequency Radio frequency defined as frequencies between 3kHz and 300GHz. This class has the lowest frequency in electromagnetic spectrum. This is the most useful class in communication field. Radio waves are divided into many classes according to their frequency and wave length. Frequency Band Wave length Applications 3- 30 KHz VLF 100 – 10 Km Sonar, fax, Navigation 30 – 300 KHz LF 10 – 1 Km Navigation 0.3 – 3 MHz MF 1 – 0.1 Km AM Broadcasting 3 – 30 MHz HF 100 – 10 m T. phones, fax, CB 30 – 300 MHz VHF 10 -1 m TV, FM Broadcasting 0.3 – 3 GHz UHF 1 – 0.1 m TV, mobile , radar 3 – 30 GHz SHF 100 – 10 mm Radar, satellite, microwave links 30 – 300 GHz EHF 10 – 1 mm Radar, wireless communication Figure 03: EM spectrum (Radio waves) and applications. Let’s consider about these frequency ranges separately.
41. 41. Very Low Frequency (VLF) Very low frequencies range is called for radio frequencies in 3 – 30 kHz which has wave length of 10 – 100 km. High bit range data cannot be transmitted such as voice because of low bandwidth. These waves can go through salt water till 40 meters. Because of high wave length these waves cannot be blocked easily. Because of above reasons this range is used in military operations often. If consider about antennas for VLF, it’s hard, impossible to establish dipoles or quarter poles because of high wave length of VLF. Antennas, which used for VLF, relatively giant and be placed in vertically. Because of inability to establish giant antennas, efficiency of radiating is laying 10% to 20% like very low. Low frequency (LF) Low frequency refers to radio frequencies in the range of 30 300 kHz. This is used for AM broadcasting in long waves. Additionally, navigation systems, air balloons, military tasks are some other applications of LF. Ground wave can cover an area with a radius of 2000 km about the transmitting antenna. By using these ground waves Radio clock concept has been introduced. In the frequency range 40 kHz–80 kHz, there are several standard time and frequency stations, such as  JJY in Japan (40 kHz and 60 kHz)  MSF in Anthorn, England (60 kHz)  WWVB in Fort Collins, Colorado, US (60 kHz)  DCF77 in Mainflingen near Frankfurt am Main, Germany (77.5 kHz)
42. 42. Medium Frequency (MF) Electromagnetic waves from 300 kHz to 3MHz series belong to medium frequency series. This frequency range is mainly utilized for AM broadcasting. Propagation occurs as ground waves. Ground wave propagation at these frequencies follows the curvature of the Earth over conductive surfaces such as the sea and damp earth. At sea, MF communications can typically be heard over several hundred miles. Furthermore, Maritime, codeless phones are some applications in medium frequencies. Figure 04: Medium frequency generator for plasma operation http://www.redline-technologies.de/index.php?File=E0ProductsHvGenerator
43. 43. High frequency (HF) Electromagnetic waves from 3MHz to 30MHz series belong to high frequency band. Wave length is between 100 to 10 meters. Not like previous bands, this band wave propagation way is different. Previous waves transmitted as ground waves. These waves propagate as sky waves. Sky wave is propagation of radio waves bent back to earth surface by ionosphere. Ionosphere is upper part of atmosphere from about 85 km to 600 km altitude. Ionosphere is divided into 4 layers. Because of ion molecules, dust, water and other particles waves are reflected back to earth. This wave band is utilized at codeless phones, land phones, fax machines, CB radios and some aviation activities. Very High Frequency (VHF) VHF band is valid from 30MHz to 300MHz frequency and wavelength of 10 meter to 1 meter. This is ideal for short distance communication. Some VHF waves are reflected by ionosphere, where some frequencies are not reflected. FM broadcasting, Television broadcasting, air navigation systems are some applications of VHFs. Usually line of sight transmission is used at VHF. This is also less affected by atmospheric noise and interference from electrical equipment than lower frequencies.
44. 44. Ultra High Frequency (UHF) UHF band is laid frequency range from 300MHz to3GHz. Wave length is between 1m to 10cm. Sky wave propagation method is used for UHF also. UHF TV signals are not carried along the ionosphere but can be reflected off of the charged particles down at another point on Earth in order to reach farther than the typical line of sight transmission distances. UHF produces short waves with higher frequencies. Because of that, no need to use bigger antennas to transmitting and receiving. Because of short waves line of sight is occurred at here. TV broadcasting, FM broadcasting, mobile communication and Radar communication are some applications of UHF. Figure 05 : A UHF antenna (MX – 075) http://www.cabletech.com.hk/index.php?product=UHF_Antenna&c=12&pp=1&p=11 64968&ph=l
45. 45. Super High Frequency (SHF) Radio frequencies in between 3GHz and 30GHz are called as SHF. Wave length of this band is between 10cm to 1cm. This is not ideal for AM or FM broadcasting because it hasn’t enough wave length for propagation. This band is referred to microwave band. By today, mobile communication uses this band for Wireless local area network, wireless USB and military tasks. Main utilizations of SHF are radar communication and microwave devices. Figure 06 : A Radar Antenna http://www.fas.org/spp/military/program/com/an-gsc-52.htm
46. 46. Extremely High Frequency (EHF) Radio frequencies in between 30GHz and 300GHz are called as SHF. Wave length of this band is between 10mm to 1mm.This cannot be used for radio broadcasting because of very short wavelength. Because of short wave length atmospheric attenuation percentage is a higher value at here. Only used in short distance communication. Usually this Band used in radio astronomy and remote sensing. Compared to other bands, small antennas are required for this band waves. Medical treatments, military tasks, security screening, weapon systems, telecommunication, scientific researchers are some typical applications of EHF. Figure 07 : Hand EHF therapy and ear EHF therapy.
47. 47. Conclusion Radio wave is one region of electromagnetic spectrum, which has lowest frequency and highest wavelength. In communication, this is the most utilized region. Radio waves again categorized according to wave properties. Very low frequencies (VLF), low frequency (LF), medium frequency (MF) are used in long way communications such as sonar, navigation and inter-continental AM broadcasting. Efficiency is very less there, because these waves are propagated as ground waves due their higher wave length and absorption by troposphere. High frequency wave (HF) is utilized at fax, land phones. Since high frequency band waves ape propagated as sky waves. Then, very high frequency (VHF) and Ultra high frequency (UHF) bands are the most familiar bands with civilians in day today life utilizations such as radio, TV broadcasting and mobile communication. Super high frequency (SHF) is also use for wireless communication and Extreme High frequency (EHF) bands are belong to smooth low distance tasks in medical, military, scientific fields. When frequency get higher its compulsory to implement in short distance applications or need to establish communication towers to make a network. With the utilization of various bands is used for different tasks in day today life and new inventions.
48. 48. Research 03 (P2.3, M2) As we know, Radio waves are one part of Electromagnetic waves. These waves are transmitted through atmosphere. On the way these waves are facing to different phenomena such as reflection, refraction, diffraction. Because of above phenomena the way of radio wave and light also is changed. This could be advantage or disadvantage or both. In Radio wave propagation both advantages and disadvantages are occurred. Let us consider these phenomena separately. Reflection Reflection can be defined as the angle of incidence is the angle of incidence is equal to the angle of reflection for a conducting surface. According to reflection surface reflection is going to be differing. If that surface is pure flat above incident is happened. If not wave is scattered due to unbalance of surface. Figure 09 : A Pure reflection without refraction.
49. 49. Refraction But in real life we can’t expect this kind of incident. While reflection, portion of wave is refracted also. refractive index is different according to mediums. According to Snell’s law, Figure 10 : refraction and reflection. According to above graph and Snell’s law,
50. 50. Diffraction Diffraction is a phenomenon, which reduce the strength of the signal. This is differing from reflection bit. This is occurs due to objectives in surround. In communication, radio waves and other waves are transmitted with above phenomena. Usually waves are transmitted in atmosphere above earth. Usually atmosphere is divided into four parts Figure 11 : Four layers of Atmosphere with dimensions.
51. 51. Troposphere The closest region is called as troposphere. This is overspread about 11 km in middle latitudes, 12 km in tropical regions, and 7km at the poles. . All mountains, Buildings and all particles we can see are in this region. Additionally, water and dust molecules are in this region also. Waves less than 30MHz frequency such as LF, MF, and VLF can be partly reflected of refracted in this region. Troposphere is compared warm other regions. This phenomenon is occurred because of heat reflection of Earth. 75% to 80% of mass of atmosphere is consisted in this region and Majority of water molecules dust molecules also in this region. In the troposphere air temperature on average decreases with height at an overall positive lapse rate of about 6.5°C per kilometer, until the tropopause, the boundary between the troposphere and stratosphere is reached. Ionosphere This is the most important region with related to wave propagation. Ionization is occurred in between thermosphere and mesosphere. This ionization area is called as Ionosphere. This consists of about 0.1% of total mass of Earth atmosphere. Ionosphere is a shell of electrons and electrically charged atoms and molecules’ stretching from about 50km to 1000km. Ionosphere is created because of ionized particles. Because of Sun (ultraviolet rays mainly) particles in this region are ionized as both (+) and (-). So, free electrons and holes are in this region and because of that radio waves are attenuated of reflected of refracted. X rays, UV rays and some other short length waves are ionized in this region. Basically all these radiations, ionizations depend on behavior of the Sun. Because of that at day time and night times behavior of ionosphere is different. Ionosphere consists of three basic layers called, D layer, E layer and F layer.
52. 52. D layer D layer is the closest layer in ionosphere towards the Earth. This is above 50km to 90kms from Earth surface. In D layer, Recombination is higher and radiation and free electron density is lower. High frequency and other waves below 10MHz are blocked by the D layer. The effect of D layer is maximum at day time and lowest at night time. The layer is chiefly generated by the action of a form of radiation known as Lyman radiation which has a wavelength of 1215 Angstroms and ionises nitric oxide gas present in the atmosphere. E layer This is the second and middle layer of ionosphere. About 90 km to 120 km above the surface of the Earth. Also called as, Kennelly – Heaviside layer. E layer is ionized because of X rays and UV rays both. Waves from 10MHz to 50MHz frequencies are reflected by this layer. The vertical structure of the E layer is primarily determined by the competing effects of ionization and recombination. The effect of E layer is maximum at daytime and minimum at night. Broadly the radiation that produces ionisation in this region has wavelengths between about 10 and 100 Angstroms. F layer F layer is outer layer of ionosphere. This is called as Appleton layer also. Extends from about 110km to 500km from earth surface. Extreme UV radiation is absorbed in this layer. This is acting as two layers at day time and one layer at night time as F1 and F2. They are found at altitudes of around 300 and 400 km in summer, and then during the winter they may fall to around 200 and 300 km. At night the two layers generally combine to form a single layer and this is generally around an altitude of 250 to 300
53. 53. km.. This is the most important layer HF wave propagation. The F layer acts as a "reflector" of signals in the HF portion of the radio spectrum enabling worldwide radio communications to be established. It is the main region associated with HF signal propagation. Radio wave is reflected by ionosphere The behavior of Ionosphere is varying with the heat/ temperature of surround. Because of that wave propagation is always depends on effect of Sun as the main Light and heat source of Earth. Atoms and molecules to split into free electrons and positive ions. When a negative electron meets a positive ion, the fact that dissimilar charges attract means that they will be pulled towards one another and they may combine. This means that two opposite effects of splitting and recombination are taking place. This is known as a state of dynamic equilibrium. Accordingly the level of ionization is dependent upon the rate of ionization and recombination. This has a significant effect on radio communications. As same as ionosphere protect Earth from hazardous rays such as X rays and high radiated UV rays. As I mentioned above, performances of layers is highest at day time. Below image gives a clear idea how these layers behave.
54. 54. Figure 12 : Behavior of ionosphere layers in day time and night time. http://www.radio-electronics.com/info/propagation/ionospheric/sun-hf-radio- propagation.php According to above graph D layer is active in daytime and it’s disappeared in night time. If consider about E layer, as same as D layer in day time. In nighttime it becomes very weak. That can be neglected the effect of E layer at night time. F layer is departed into two different layers as F1 and F2 in day time. Although, Those two layers recombine as one layer at night time. Because of this behavior of ionosphere, (low absorption of waves) we can hear many sounds clearly than day time in practically. Sky wave propagation can be varied according to season also. There are four seasons on Earth affected on some countries. As an example, in summer, effect of sun is higher and radiation and ionization is higher of ionosphere. So, even low frequencies are absorbed of reflected back to Earth. As an example there is less absorption and wide area communication in winter compared to summer. Behavior of sun is changed in every 27 days, because of rotation and every 11 years, because of sun spots. The overall effect on HF communications is that there will be higher critical frequencies occur for every 11 years.
55. 55. Conclusion A wave can be described as a disturbance that travels through a medium from one location to another location under effect of wave phenomena. Radio waves in electromagnetic spectrum mainly transmitted through the atmosphere as ground wave propagation, line of sight propagation or sky wave propagation. Ionosphere of Earth is divided into four layers as troposphere, Stratosphere, Mesosphere and Thermosphere. Ionosphere is made because of ionized particles in between Stratosphere and Mesosphere regions. In particular the ionosphere is widely known for affecting signals on the short wave radio bands where it "reflects" signals enabling these radio communications signals to be heard over vast distances. This is again divided into three layers as D, E & F. radio frequency phenomena occur due to these layers in HF, VHF bands mainly. The behavior of these layers mainly depend on Sun. Radiation of sun, atoms are ionized as electrons or holes and make barriers. Because of that behavior of those layers are changed according to daily, seasonal, long term variations and that affects on radio wave communication as broadcasting efficiency, power level (quality), transmitting distance and magnitude coverage area.
56. 56. Research 04 (P2.4, D3) In above researches we considered about different wave types of radio waves and those waves are differ according to their properties such as frequency, wave length, etc. Usually radio waves are travelling through atmosphere from transmitter to receiver. According to properties of radio waves, method of propagation is varied. There are few main methods of propagation such as ground wave, sky wave, space wave and line of sight propagation. Ground Wave Propagation Long and medium bands of radio waves such as VLF, LF, and MF have higher wavelength and frequency below 2MHz. Ground wave radio propagation is used to provide relatively long radio communications coverage and used in long way communication such as AM Radio broadcasting and military operations. According to Steve Winder and Joe Carr (2002), “Waves in the bands from very low frequencies (VLF, 3–30 kHz), low frequencies (LF, 30–300 kHz) and medium frequencies (MF, 300–3000 kHz) travel close to the earth’s surface: the ground wave Transmissions using the ground wave must be vertically polarized to avoid the conductivity of the earth short-circuiting the electric field.” As mentioned in Ian Poole (2003), “The ground wave is only signals below about 2MHz. it is found that as a frequency increases the attenuation of the whole signal increases and the coverage is considerably reduced. Obviously the exact range will be depending on many factors. Typically a high power medium wave station may be heard over distances 150km and more. There are also many low power stations running 100W or so. These might have a coverage area extending to 15 or 20 miles.” Ground waves are useful at day time, because medium frequencies can be absorbed by the D region of ionosphere. Ground waves travel very close to earth. These waves propagate from transmitter to receiver. Usually these waves’ propagating is affected on troposphere objects such as natural and syntactic objects and even surface properties of the Earth. There is another type of
57. 57. ground wave, which follow the curvature of Earth. These waves called as surface wave. Antennas, which use for ground wave transmit and receive are relatively bigger. Even in other way broadcasting, ground wave propagation might be occurred as a side effect. Polarization of antenna is also affect on propagating efficiency. Vertical polarized antenna has better efficiency than horizontal polarized antenna, because horizontally polarized ground wave would be shorted out by the conductivity of the ground. Surface wave propagation. http://www.ustudy.in/node/5139 Sky Wave Propagation Sky wave propagation can be defined as, the propagation of radio waves refracted to towards the Earth by the ionosphere. High frequency (3MHz to 30MHz) broadcasting is occurred due to sky wave propagation. According to Steve Winder and Joe Carr (2002), “Radio signals travelling away from the earth’s surface are called as sky waves and they reach the layers of ionosphere.” Especially, High frequency waves are reflected by ionization of atmosphere. Sky wave propagation can be vary according to time of the day or season.