.

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2. Electromagnetics Spectrum

3. The Microwave spectrum as shown above is a very broad spectrum. Based on certain general RF transmission properties, the spectrum is divided into several application bands. As far as we are concerned , we are interested in DMR systems, which is used for terrestrial application. So for our application the useable band starts from 2Ghz and ends somewhere near 30 Ghz. The 30GHz band is used for Satellite Communication.The Microwave spectrum as shown above is a very broad spectrum. Based on certain general RF transmission properties, the spectrum is divided into several application bands. As far as we are concerned , we are interested in DMR systems, which is used for terrestrial application. So for our application the useable band starts from 2Ghz and ends somewhere near 30 Ghz. The 30GHz band is used for Satellite Communication.

4. What are the different methods of Communication ? For Access, the subscriber gadget can be wired through copper to the switch, or it can be multiplexed on a Fiber with several other subscribers, or for faster deployment of the network , even certain wireless communication technologies like WLL can be used to provide access. The communication through Satellite, for this application, is not preferred for voice due to problems of delay but it can be used for data communication.What are the different methods of Communication ? For Access, the subscriber gadget can be wired through copper to the switch, or it can be multiplexed on a Fiber with several other subscribers, or for faster deployment of the network , even certain wireless communication technologies like WLL can be used to provide access. The communication through Satellite, for this application, is not preferred for voice due to problems of delay but it can be used for data communication.

5. When terminals are connected we are used to thinking in terms of hookups. A current may flow through the hookup wire depending on the voltages that were present before we connected. The wire is assumed to have little or no resistance so by connecting, the two terminals are forced to be at the same voltage. These assumptions are okay if the signal is not changing too quickly. This means that the frequency of a sinusoidal signal is not too high or the risetime of a digital signal not too small. The way we consider electrical connections depends on the relative size of a wavelength or propagating distance during a risetime to the size of the object with which we are dealing. For example, a power engineer working at 50 or 60Hz will consider the power grid a transmission line. A 60Hz sine wave has a wavelength of about 5,000km. A 2GHz sine wave has a wavelength of 15cm. When terminals are connected we are used to thinking in terms of hookups. A current may flow through the hookup wire depending on the voltages that were present before we connected. The wire is assumed to have little or no resistance so by connecting, the two terminals are forced to be at the same voltage. These assumptions are okay if the signal is not changing too quickly. This means that the frequency of a sinusoidal signal is not too high or the risetime of a digital signal not too small. The way we consider electrical connections depends on the relative size of a wavelength or propagating distance during a risetime to the size of the object with which we are dealing. For example, a power engineer working at 50 or 60Hz will consider the power grid a transmission line. A 60Hz sine wave has a wavelength of about 5,000km. A 2GHz sine wave has a wavelength of 15cm.

6. What is a transmission line? A transmission line is a device used to efficiently carry energy between two points It has mechanical and electrical stability. It is designed to have minimal loss. Transmission lines play an important role in wireless communication systems. They carry the RF signal froman RF source inside the base station. They also carry the signal out of the base station up the feedline to the transmit antennas. On the receive side, they carry the signal back from the antennas. Transmission lines are one of the "wires" in "wireless" RF cables, and waveguides are examples of transmission lines. Your cable TV coax cable is an example of a transmission line at home.Transmission lines play an important role in wireless communication systems. They carry the RF signal froman RF source inside the base station. They also carry the signal out of the base station up the feedline to the transmit antennas. On the receive side, they carry the signal back from the antennas. Transmission lines are one of the "wires" in "wireless" RF cables, and waveguides are examples of transmission lines. Your cable TV coax cable is an example of a transmission line at home.

7. Common Transmission Lines Transmission lines are designed to efficiently carry energy from one point to another while maintaining a constant characteristic impedance. Shown here are three common types of transmission lines. Coaxial cable is very common in RF wireless systems. Commonly defined simply as "coax," it is usually identified by terms like "RG" and a number. For example "RG-9" or "RG-41". If you have cable TV, you probably are using RG-9 cable. It has a characteristic impedance of 75 ohms. We will go into that later. If you have an outdoor T antenna, or an FM antenna, the cable that leads to it is 300 ohm twinaxial cable. Finally, microstrip transmission lines are usually found on circuit boards, or inside the RF components of a base station, radio, or some RF test equipment. It is usually used at microwave frequencies > 16 Hz.Shown here are three common types of transmission lines. Coaxial cable is very common in RF wireless systems. Commonly defined simply as "coax," it is usually identified by terms like "RG" and a number. For example "RG-9" or "RG-41". If you have cable TV, you probably are using RG-9 cable. It has a characteristic impedance of 75 ohms. We will go into that later. If you have an outdoor T antenna, or an FM antenna, the cable that leads to it is 300 ohm twinaxial cable. Finally, microstrip transmission lines are usually found on circuit boards, or inside the RF components of a base station, radio, or some RF test equipment. It is usually used at microwave frequencies > 16 Hz.

8. A 300 Ohm Twin-Lead Balanced Line Widely Used on TV Antennas

9. More Common Transmission Lines Another common type of transmission line is waveguide. Another type of transmission line commonly found in RF or wireless communication systems is called waveguide. It is basically a pipe but with very precise dimensions (we will see why later). It can have a circular, elliptical, or rectangular cross section. The smaller the site, the higher the frequency band it operates on. Waveguides are usually used in the feeds for the microwave backhaul to the main branch office at remote cell sites. Waveguides are usually kept pressurized with nitrogen or other inert gas in order to prevent water vapor from building up inside. Waveguide is more prevalent in high power microwave applications (as is the case for the feeds to the microwave backhaul antennas). Never look into the open end of a waveguide if you do not know what is going on at the other end! You can suffer permanent eye damage. At high power levels, it is like sticking your hand in a microwave oven, especially at frequency near 2.5 GHz. The most common type of waveguide in RF communication systems is elliptical. It is flexible and can be transported on large rolls just like coax. Another type of transmission line commonly found in RF or wireless communication systems is called waveguide. It is basically a pipe but with very precise dimensions (we will see why later). It can have a circular, elliptical, or rectangular cross section. The smaller the site, the higher the frequency band it operates on. Waveguides are usually used in the feeds for the microwave backhaul to the main branch office at remote cell sites. Waveguides are usually kept pressurized with nitrogen or other inert gas in order to prevent water vapor from building up inside. Waveguide is more prevalent in high power microwave applications (as is the case for the feeds to the microwave backhaul antennas). Never look into the open end of a waveguide if you do not know what is going on at the other end! You can suffer permanent eye damage. At high power levels, it is like sticking your hand in a microwave oven, especially at frequency near 2.5 GHz. The most common type of waveguide in RF communication systems is elliptical. It is flexible and can be transported on large rolls just like coax.

10. How fast do waves travel? Coaxial line, air filled 30cm/nsec (1ft./nsec) Coaxial line, teflon filled 20cm/nsec Microstrip 15cm/nsec The phase velocity of the wave depends on the medium.It is the velocity of the phase of the wave, just as if you were surfing along the transmission line. In air or vacuum the speed is the speed of light which is approximately 186,000 miles/sec or 300,000,000 meters/sec. In a medium or dielectric, the speed will be slower. The fraction of the velocity of light is called the velocity factor. Air has a velocity factor of 1.00 Teflon about 0.65 The speed of light is usually given the symbol “c.” So c = 3 × 108 m/sec expressed in scientific notation. You may hear the term group velocity or group delay. This has to do with the velocity of propagation of the envelope or modulation of the wave. In coaxial transmission lines (which are usually regarded to be almost perfect), the phase and group velocities are the same. In waveguide the phase and group velocities will be different. In elliptical, flexible waveguide a typical group delay is 140nsec/100ft. The group velocity as a percentage of light velocity will vary from 60% to 80% over the waveguide frequency range.The phase velocity of the wave depends on the medium.It is the velocity of the phase of the wave, just as if you were surfing along the transmission line. In air or vacuum the speed is the speed of light which is approximately 186,000 miles/sec or 300,000,000 meters/sec. In a medium or dielectric, the speed will be slower. The fraction of the velocity of light is called the velocity factor. Air has a velocity factor of 1.00 Teflon about 0.65 The speed of light is usually given the symbol “c.” So c = 3 × 108 m/sec expressed in scientific notation. You may hear the term group velocity or group delay. This has to do with the velocity of propagation of the envelope or modulation of the wave. In coaxial transmission lines (which are usually regarded to be almost perfect), the phase and group velocities are the same. In waveguide the phase and group velocities will be different. In elliptical, flexible waveguide a typical group delay is 140nsec/100ft. The group velocity as a percentage of light velocity will vary from 60% to 80% over the waveguide frequency range.

11. Microwave beam passes through that part of the atmosphere , which is in close proximity with the surface of the earth. This is called the troposphere. It is quite natural , therefore , that the physical properties of the atmosphere and the terrain should have effect on the propagation of radio waves in microwave systems. Since radio waves , like light waves are also electromagnetic waves, though of lesser frequency, they also have all the properties of light waves like attenuation, refraction, reflection, diffraction, scattering and polarization. While designing the system and engineering the link, the effect of all these are to be taken into consideration.Microwave beam passes through that part of the atmosphere , which is in close proximity with the surface of the earth. This is called the troposphere. It is quite natural , therefore , that the physical properties of the atmosphere and the terrain should have effect on the propagation of radio waves in microwave systems. Since radio waves , like light waves are also electromagnetic waves, though of lesser frequency, they also have all the properties of light waves like attenuation, refraction, reflection, diffraction, scattering and polarization. While designing the system and engineering the link, the effect of all these are to be taken into consideration.

13. Refraction is a property of electromagnetic waves which is due to different speed of wave in different media. It is a well known property of the light waves that when it travels from a medium of higher refractive index to a medium of lower refractive index the rays move away from the normal to the surface. This is so since the velocity of light waves is more in the media with lower refractive index than that with the higher one. And, of course the velocity is maximum in vacuum. The radio waves also behave in the similar fashion to the light waves. A normal microwave system works on the principle of LOS , with the transmitting and receiving antennas located on high towers, and obviously the radio beam is horizontal so any change in height affects the LOS propagation. Refraction is a property of electromagnetic waves which is due to different speed of wave in different media. It is a well known property of the light waves that when it travels from a medium of higher refractive index to a medium of lower refractive index the rays move away from the normal to the surface. This is so since the velocity of light waves is more in the media with lower refractive index than that with the higher one. And, of course the velocity is maximum in vacuum. The radio waves also behave in the similar fashion to the light waves. A normal microwave system works on the principle of LOS , with the transmitting and receiving antennas located on high towers, and obviously the radio beam is horizontal so any change in height affects the LOS propagation.

14. If a radio beam is propagated in free space, where there is no atmosphere , the path followed by the beam is a straight line. A radio beam propagated through earth's atmosphere encounters variations in the atmospheric refractivity index along its trajectory that causes the ray path to become curved. Atmosphere gases will absorb and scatter the radio path energy, the amount of absorption and scattering being a function of frequency and altitude. The effect of refraction is to cause the beam to deviate from its line-of-sight straight path. Refractivity of the atmosphere will affect not only the curvature of the ray path but also give some insight into fading phenomenon. Its effect on transmission could be very serious, causing outages of a fraction of a second to several hours. If a radio beam is propagated in free space, where there is no atmosphere , the path followed by the beam is a straight line. A radio beam propagated through earth's atmosphere encounters variations in the atmospheric refractivity index along its trajectory that causes the ray path to become curved. Atmosphere gases will absorb and scatter the radio path energy, the amount of absorption and scattering being a function of frequency and altitude. The effect of refraction is to cause the beam to deviate from its line-of-sight straight path. Refractivity of the atmosphere will affect not only the curvature of the ray path but also give some insight into fading phenomenon. Its effect on transmission could be very serious, causing outages of a fraction of a second to several hours.

15. The angle of curvature caused by refraction is denoted by the K-factor, which is defined as the ratio of the effective earth radius to the true earth radius. The effective earth radius is not the radius of the microwave beam, it the radius of the fictitious earth which causes the microwave beam to be drawn as the straight line, for a given atmospheric condition.The angle of curvature caused by refraction is denoted by the K-factor, which is defined as the ratio of the effective earth radius to the true earth radius. The effective earth radius is not the radius of the microwave beam, it the radius of the fictitious earth which causes the microwave beam to be drawn as the straight line, for a given atmospheric condition.

16. Atmospheric Refraction cause microwave beam to be trapped in an atmospheric waveguide called a duct, resulting in severe transmission disruption. Ducting is usually caused by low-altitude, high-density atmospheric layers, most frequently occurring near or over large expanses of water or in climates where temperature or humidity inversions occur.When the beam enters the duct and it reaches the other interface between the two density layers, the critical angle is exceeded so that internal reflection occurs. Subsequently the beam bounces back and forth as it travels along the duct, and the receiving antenna looses the signal.Atmospheric Refraction cause microwave beam to be trapped in an atmospheric waveguide called a duct, resulting in severe transmission disruption. Ducting is usually caused by low-altitude, high-density atmospheric layers, most frequently occurring near or over large expanses of water or in climates where temperature or humidity inversions occur.When the beam enters the duct and it reaches the other interface between the two density layers, the critical angle is exceeded so that internal reflection occurs. Subsequently the beam bounces back and forth as it travels along the duct, and the receiving antenna looses the signal.

17. The scattering of microwaves by rain precipitation is very important at frequencies above about 10 Ghz. At these frequencies the rain droplet sizes become appreciable in comparison to the wavelength of the radio waves in water and hence these droplets cause scattering of microwave energy . The main effect of scattering is a heavy attenuation in the path. Since the size of water drops are slightly elongated and canted due to the effect of gravity, the loss of the horizontally polarized wave is slightly higher than that for the vertically polarized wave. The important effect of rain drops on microwave beam is depolarization of the signal. This happens due to non-spherical dimensions of the droplets. This phenomenon is important if cross-polarized channels are in use. However, it should be appreciated that scattering and depolarization effect takes place simultaneously and, therefore, the overall effect on system outage is not additive.The scattering of microwaves by rain precipitation is very important at frequencies above about 10 Ghz. At these frequencies the rain droplet sizes become appreciable in comparison to the wavelength of the radio waves in water and hence these droplets cause scattering of microwave energy . The main effect of scattering is a heavy attenuation in the path. Since the size of water drops are slightly elongated and canted due to the effect of gravity, the loss of the horizontally polarized wave is slightly higher than that for the vertically polarized wave. The important effect of rain drops on microwave beam is depolarization of the signal. This happens due to non-spherical dimensions of the droplets. This phenomenon is important if cross-polarized channels are in use. However, it should be appreciated that scattering and depolarization effect takes place simultaneously and, therefore, the overall effect on system outage is not additive.

18. Reflections The lossless transmission line terminated with an impedance equal to it’s own characteristic impedance is an ideal situation. However, this is approached, but rarely achieved in practice. The following section examines the transmission line when terminated with some other impedance. The first cases to examine are a line that is shorted and a line left open. This may seem extreme. Why would a transmission line be shorted? There are legitimate uses for shorted lines, however asking the questions about shorted and open lines will give us valuable insight about transmission lines. The lossless transmission line terminated with an impedance equal to it’s own characteristic impedance is an ideal situation. However, this is approached, but rarely achieved in practice. The following section examines the transmission line when terminated with some other impedance. The first cases to examine are a line that is shorted and a line left open. This may seem extreme. Why would a transmission line be shorted? There are legitimate uses for shorted lines, however asking the questions about shorted and open lines will give us valuable insight about transmission lines.

19. A microwave beam may have only 1 or 2 deg half power beamwidth, this still represents a large area of energy spread at a distance of 40km from the transmitter. Simple geometry indicates the half power cone to have enlarged to a circle of approximately 1.4km in diameter for a 2 deg beam. This means that some energy will be reflected form ground. Radio waves are reflected from ground, buildings, marshy land, and most importantly by water sheet over lakes,rivers and sea etc. During the reflection the waves suffer a loss. The ratio of incident wave amplitude to that of the reflected wave amplitude is called the reflection coefficient. For water it is almost 1 At a receiving antenna, energy arrives from the direct and the reflected paths. If the two waves are in phase, there is an enhancement of the signal, but if the waves are out of phase, a cancellation occurs which can disrupt transmission. This 180 deg phase shift occurs for horizontally polarized waves at microwave frequencies whereas for vertically polarized waves, the phase shift can be between 0 and 180deg depending upon ground conditions and angle of incidence.A microwave beam may have only 1 or 2 deg half power beamwidth, this still represents a large area of energy spread at a distance of 40km from the transmitter. Simple geometry indicates the half power cone to have enlarged to a circle of approximately 1.4km in diameter for a 2 deg beam. This means that some energy will be reflected form ground. Radio waves are reflected from ground, buildings, marshy land, and most importantly by water sheet over lakes,rivers and sea etc. During the reflection the waves suffer a loss. The ratio of incident wave amplitude to that of the reflected wave amplitude is called the reflection coefficient. For water it is almost 1 At a receiving antenna, energy arrives from the direct and the reflected paths. If the two waves are in phase, there is an enhancement of the signal, but if the waves are out of phase, a cancellation occurs which can disrupt transmission. This 180 deg phase shift occurs for horizontally polarized waves at microwave frequencies whereas for vertically polarized waves, the phase shift can be between 0 and 180deg depending upon ground conditions and angle of incidence.

20. The property of diffraction manifests as bending of the electromagnetic wave around any obstacle like a sharp 'knife edge' or a 'spherical' surface. The property is explained by assuming that the every point on the wavefront has the property of generating secondary waves. Thus it is not necessary for the signal to be received only through Line of Sight. Diffraction of a radio wave occurs when the wave front encounters an obstacle that is large when compared to the wavelength of the ray. Diffraction is of two types, which is based on the obstacle which causes diffraction. Highly efficient paths like water or desert are often termed as smooth sphere diffraction paths. These are nothing but reflecting surfaces. The majority of microwave paths have obstacle clearance in the category of knife- edge diffraction. These paths traverse terrain which is moderately to severely rough with brush or tree covering. Diffraction occurs when a beam passes over an obstacle with grazing incidence ( just touching the obstacle). The beam energy is dispersed by an amount which depends on the size and the shape of the obstacle. Shadow loss is the term used to describe the loss in an area behind the obstacle. This loss is dependent on the frequency. The property of diffraction manifests as bending of the electromagnetic wave around any obstacle like a sharp 'knife edge' or a 'spherical' surface. The property is explained by assuming that the every point on the wavefront has the property of generating secondary waves. Thus it is not necessary for the signal to be received only through Line of Sight. Diffraction of a radio wave occurs when the wave front encounters an obstacle that is large when compared to the wavelength of the ray. Diffraction is of two types, which is based on the obstacle which causes diffraction. Highly efficient paths like water or desert are often termed as smooth sphere diffraction paths. These are nothing but reflecting surfaces. The majority of microwave paths have obstacle clearance in the category of knife- edge diffraction. These paths traverse terrain which is moderately to severely rough with brush or tree covering. Diffraction occurs when a beam passes over an obstacle with grazing incidence ( just touching the obstacle). The beam energy is dispersed by an amount which depends on the size and the shape of the obstacle. Shadow loss is the term used to describe the loss in an area behind the obstacle. This loss is dependent on the frequency.

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22. Wavelength, mobile phone Mobile phone operates at about 900 MHz and 1,800 MHz Wavelength is about 33 cm and 1.667 cm Here is an application where transmission line techniques may be considered.Here is an application where transmission line techniques may be considered.

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24. Mobile Phone Manufacturer Model SAR (W/kg) BoschM-Com 906 1.32 BoschWorld-718 0.33 BoschGSM-908 1.59 Motorola130 Startac0.10 MotorolaStarTac 70 0.02 Motorolad160 0.81 Motorolacd930 0.70 Motorola V3688 0.02 Motorola16111 1.06  Nokia 2110 0.44  Nokia3110 1.24  Nokia3210 1.14  Nokia6110 0.8 Nokia8810 0.22  PanasonicEB-G250 0.95  SiemensC25 0.72 SharpTQ G700 1.01  SonyCMDX-1000 0.41  SonyCMD-C1 0.55

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26. Comments on Confused Studies In 1995, researchers at the University of Washington, Seattle, ?found DNA breaks in cells exposed to wireless phone radiation. ? Subsequent attempts by researchers at Washington University in St. Louis to duplicate the work were unsuccessful, an indication that the first work might have been flawed. One American research group showed a near tripling of a statistically significant risk of a rare kind of tumor called a neurocytoma among cell phone users, compared with people who do not use cell phones. The result of that study, however, is undercut by the fact that the data did not show that the risk of neurocytoma rose with the amount of cell phone use, which researchers would have expected to find. In fact, greater exposure was associated with lower risk. Another epidemiological study found that ? right-handed people who used cell phones and had brain tumors tended to have them on the right side of the head. ?However, no such correlation appeared in left-handed cancer patients.

27. In 1997,researchers at the Royal Adelaide Hospital in Australia spent 18 months exposing mice to radiation mimicking the emissions of digital mobile phones and found that twice as many of these mice developed lymphomas as did animals not exposed to the radiation. But since then, three other teams have failed to find similar evidence of increased cancer rates among mice exposed to microwave emissions. A team of microwave experts at the Brooks Air Force Base in San Antonio, Texas, used mice genetically engineered to be susceptible to breast tumors. They exposed the animals to microwaves for 20 hours a day for 18 months, yet saw no increases in tumor rates. Researchers in Australia have repeated the original experiment using the same strain of mice and exposure conditions. "If they don't come up with the same result, that'll be a happy outcome," the Australia team says.

28. A team at the Veterans Affairs Medical Center in California, found that mice exposed to microwaves for two hours a day were less likely to develop brain tumors when given a cancer-causing chemical. But nobody has yet replicated that finding either. In 1998, at the Defense Evaluation and Research Agency's labs (UK). A scientist exposed slices of rat brain to microwave radiation and found that it blunted their electrical activity and weakened their responses to stimulation. The results were seized upon as further evidence that mobile phones could scramble human memories. The latest findings have undermined fears about memory loss. One result, suggests that nerve cell synapses exposed to microwaves become more--rather than less--receptive to undergoing changes linked to memory formation.

29. Microwave Oven

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32. How do microwave ovens work? operate on a frequency of 2450 megahertz Larger ovens used for industrial applications operate at 915 MHz.

33. microwave cooking significantly changes food nutrients. there may be a loss of some vitamins. Some protective properties may be destroye. After eating microwaved food, cholesterol levels increased. Increases white blood cell numbers. Decreases red blood cell numbers.

34. IRPA (International Radiation Protection Association) Guidelines: recommends exposure limit of 5 mW/cm2 for RF workers and 1 mW/cm2 for the general public. These exposure limits are averaged over 6 minutes (0.1 h) period. a GSM cellular phone may emit up to 1 W at 1800 MHz, which is 2 mW/cm2 at 5 cm

36. RADIATION-PATTERNS If the radiator transmits equally in all directions then it is called Isotropic radiator. The power density at any point in the space - Spherical Distribution of Power RADIATION-PATTERNS If the radiator transmits equally in all directions then it is called Isotropic radiator. The power density at any point in the space - Spherical Distribution of Power

37. Radiation-Patterns If the antenna radiates only in a particular direction or directions it is called directional antenna. Since the antenna is directional, it will have gain in the direction of transmission. This gain is relative to the isotropic antenna Gain is maximum in a direction called the Boresite. The shape of power distributed is called the Radiation Pattern Radiation-Patterns If the antenna radiates only in a particular direction or directions it is called directional antenna. Since the antenna is directional, it will have gain in the direction of transmission. This gain is relative to the isotropic antenna Gain is maximum in a direction called the Boresite. The shape of power distributed is called the Radiation Pattern

38. Radiation Pattern : Gain plotted on a polar chart. Various circles indicate constant gain scales. The outermost is usually 50dBi gain and the innermost - OdBi Definition of gain : It is the ratio of power measured at a point , transmitted by an antenna to the power measured at the same point transmitted by an isotropic antenna.Radiation Pattern : Gain plotted on a polar chart. Various circles indicate constant gain scales. The outermost is usually 50dBi gain and the innermost - OdBi Definition of gain : It is the ratio of power measured at a point , transmitted by an antenna to the power measured at the same point transmitted by an isotropic antenna.

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45. Metal Detector

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47. Electric Line Safety       Overhead Electric LinesElectrical energy constantly seeks a path to the ground. When you are working around electric overhead lines. Watch where you are going.Stay clear. Don’t touch. Underground Electric LinesDigging, drilling or blasting can damage these underground lines and cause electrocution or fire.

53. In Industry-A paint spraying- Electrodeposite-Electrochemical Machining-Separation of fine partical In Agriculture Sort seed Direct sprays to plants Measure the moisture content of cropps Spine cotton Speed baking of bread Smoking of meat