Antenna and Wave Propagation PDF

Department of Engineering E&E Section Antenna and Wave Propagation Reference Links https://ebookcentral.proquest.com/lib/momp/ reader.action? docID=1645674&query=Radio+Wave+Propagation+Fund amentals+%28Artem+Saakian%29 https://ebookcentral.proquest.com/lib/momp/ detail.action?docID=4205879&query=...

Department of Engineering E&E Section Antenna and Wave Propagation Reference Links https://ebookcentral.proquest.com/lib/momp/ reader.action? docID=1645674&query=Radio+Wave+Propagation+Fund amentals+%28Artem+Saakian%29 https://ebookcentral.proquest.com/lib/momp/ detail.action?docID=4205879&query=antenna https://ebookcentral.proquest.com/lib/momp/ reader.action?docID=338762&ppg=7 https://ebookcentral.proquest.com/lib/momp/ detail.action?docID=4205879&query=antenna https://ebookcentral.proquest.com/lib/momp/ reader.action? docID=433804&query=radio+imaging+system# https://ebookcentral.proquest.com/lib/momp/ detail.action?docID=4205879&query=antenna https://ebookcentral.proquest.com/lib/momp/ reader.action? docID=1645674&query=Radio+Wave+Propagation+Fund amentals+%28Artem+Saakian%31 https://ebookcentral.proquest.com/lib/momp/  Outcome # 4 Evaluate the fundamental antenna parameters for effective radiation.  Outcome # 5 Analyze antenna arrays for isotropic point sources and dipoles. Outcome # 6 Determine and analyze the radiation patterns of different types of antennas.  Among the antenna parameters, the effective length and effective area are also important. These parameters help us to know about the antenna’s performance. Effective length  Antenna Effective length is used to determine the polarization efficiency of the antenna.  Definition− “The Effective length is the ratio of the magnitude of voltage at the open terminals of the receiving antenna to the magnitude of the field strength of the incident wave front, in the same direction of antenna polarization.”  When an incident wave arrives at the antenna’s input terminals, this wave has some field strength, whose magnitude depends upon the antenna’s polarization. This polarization should match with the magnitude of the voltage at receiver terminals.  Definition − “Effective area is the area of the receiving antenna, which absorbs most of the power from the incoming wave front, to the total area of the antenna, which is exposed to the wave front.”  The whole area of an antenna while receiving, meets the incoming electromagnetic waves, whereas only some portion of the antenna, receives the signal, known as the effective area.  Only some portion of the received wave front is utilized because some portion of the wave gets scattered while some gets dissipated as heat.  Hence, without considering the losses, the area, which utilizes the maximum power obtained to the actual area, can be termed as effective area.  Effective area is represented by A. eff Scattering Parameters S-parameters describe the input-output relationship between ports (or terminals) in an electrical system. Suppose if we have 2 ports (Port 1 and Port 2), then S12 represents the power transferred from Port 2 to Port 1. S represents the power transferred from Port 1 to 21 Port 2. In general, S NM represents the power transferred from Port M to Port N in a multi-port network. Scattering Parameters Scattering parameters describes the input-output relationships between ports in an electrical system.  Specifically at high frequency it becomes essential to describe a given network in terms of waves rather than voltage or current. Thus in S-parameters we use power waves. Scattering Parameters Thus in S-parameters we use power waves. For a two-port network, s-parameters can be defined as DUT – Device under Test Scattering Parameters Thus in S-parameters we use power waves. For a two-port network, s-parameters can be defined as S11 is the input port voltage reflection coefficient S12 is the reverse voltage gain S21 is the forward voltage gain S22 is the output port voltage reflection coefficient Scattering Parameters Thus in S-parameters we use power waves. The S-parameter matrix can be used to determine reflection coefficients and transmission gains from both sides of a two port network. This concept can further be used to determine s-parameters of a multi port network. These concepts can further be used in determining Gain, Return loss, VSWR and Insertion Loss.  ANTENNA AND PROPAGATION Near Field and Far Field. Antennas produce two sets of fields, the near field and the far field. The near field describes the region directly around the antenna where the electric and magnetic fields are separate. These fields are not the radio wave, but they do indeed contain any information transmitted. These fields weaken with the distance from the antenna, approximately by the quadruple power of the distance. The near field is also referred to as the Fresnel zone. The far field that is approximately 10 wavelengths from the antenna is the radio wave with the composite electric and magnetic fields. For example, at 2.4 GHz, one wavelength is 984/2400 = 0.41 feet (3m = 9.84 feet / 1m =3.28084 feet). The far field is 10 times that, or 4.1 ft or beyond.  ANTENNA AND PROPAGATION Near Field and Far Field.  ANTENNA AND PROPAGATION Near Field and Far Field. The fields surrounding an antenna are divided into 3 main regions: Reactive Near Field The reactive near field and the radiating near field. The reactive near field is the region where the fields are reactive i.e the E and H fields are out of phase by 90 degrees to each other. For propagating or radiating fields, the fields must be orthogonal to each other but in phase. Radiating Near Field (Fresnel region) The radiating near field or Fresnel region is the region between the reactive near and far field. The reactive fields do not dominate in this region. This is the region where the EM fields start to transition from reactive to radiating fields. However unlike the far field region, the shape of the radiation pattern varies significantly with distance. Far Field The far field is the region that is at a large distance from the antenna. In the far field the radiation pattern does not change shape as the distance increases. In this region, the EM fields are dominated by radiating fields. The E and H-fields are orthogonal to each other and to the direction of propagation as with plane waves. One condition that must be met when making measurements in the far field region is that the distance from the antenna must be much greater than the size of the antenna and the wavelength.  ANTENNA AND PROPAGATION Near Field and Far Field.  ANTENNA AND PROPAGATION Near Field and Far Field. Most wireless applications use the far field wave. Any antenna radiation patterns are valid only if measurements are taken on the far field. The near field is rarely used, but applications such as radio-frequency identification (RFID) and near field communication (NFC) make use of the near field. Some cell phone manufacturers also build in a short- range near field radio for applications such as wireless building access, ticket purchases, or automotive functions.  Calculate the Reactive, Radiating Near Field Distance & Far Field Distance of an antenna with a length of 3.2 m, operating with a frequency of 1200 MHz.  Calculate the Reactive, Radiating Near Field Distance & Far Field Distance of an antenna with a length of 3.2 m, operating with a frequency of 1200 MHz.  Wavelength, λ = 0.2498 m  Reactive Near Field Distance ≤ 7.1 m  Radiating Near Field Distance ≤ 81.9767 m  Far Field (Greater than this distance) ≥ 81.9767 m Antenna and Propagation Radiation pattern The power when radiated from the antenna has its effect in the near and far field regions. Graphically, radiation can be plotted as a function of angular position and radial distance from the antenna. Radiation pattern is a three dimensional quantity which involves the variation of field or power proportional to the field squared. This is a mathematical function of radiation properties of the antenna represented as a function of spherical co- ordinates, E (θ, Ø) and H (θ, Ø). Where is the angle measured off the z-axis, and is the angle measured counterclockwise off the x-axis.  RADIATION PATTERN OF A DIPOLE Chapter –1 ANTENNA. Antenna and Propagation Radiation pattern Antenna and Propagation  Antenna Radiation Patterns Common parameters Main lobe (boresight) Half-power beam width (HPBW) Front-back ratio (F/B) Pattern nulls Typically measured in two planes: Vector electric field referred to E-field Vector magnetic field referred to H-field Antenna Pattern Parameters  Antenna and Propagation Radiation pattern Radiation properties Power flux density Radiation intensity Field strength Directivity Phase  The radiation property of most concern is Polarization either two- or three dimensional spatial distribution of radiated energy as a function of the observer’s position along a path or surface of constant radius. The field radiation pattern can be expressed completely w.r.t. field intensity and polarization using 3 factors. (1) Eθ (θ, ) →The θ-component of the electric field as a function of angles θ and  (v/m) (2) E (θ, ) → The  -component of electric field as a function of angle θ and  (v/m) (3) δθ(θ, ) or δ(θ, ) → The phase angles of both the field components (deg. Or rad.)  Antenna and Propagation Radiation pattern The field pattern is expressed in terms of relative field pattern which is commonly called normalized field pattern. The normalized field pattern is defined as the ration of the field component to its max. value. Normalized field pattern is a dimensionless quantity with max. value =1. The normalized field patterns for θ and  components of Electric Field are given as Eθn (θ, ) = Eθ (θ, ) / Eθ (θ, ) max. Similarly En (θ, ) = E (θ, ) / E (θ, ) max. The half power level occurs at those angles θ and  for which Eθn (θ, ) = 1/√2 = 0.707. At distances that are large compared to the size of the antenna and large compared to the wavelength, the shape of the field pattern is independent of distance. Usually the patterns of interest are for this far-field condition.  Antenna and Propagation Radiation pattern Normalizing this power w.r.to its maximum value yields a normalized power pattern as a function of angle which is a dimensionless number with a maximum value of unity. Normalized power pattern = Pθn (θ, ) = S (θ, ) / S (θ, ). max S (θ, ) = Poynting vector =[ E2θ (θ, ) + E2  (θ, ) ]/Z0 , W/m2 Z0 = intrinsic impedance of space = 376.7 Ω S (θ, ) max = Maximum value of S (θ, ) , W/m2 Antenna and Propagation 3-Dimensional Radiation Pattern : Example radiation pattern for an Antenna Types of Radiation patterns Omni-directional pattern (also called non-directional pattern): The pattern usually has a doughnut shape in three-dimensional view. However, in two-dimensional view, it forms a figure-of-eight pattern. Pencil-beam pattern − The beam has a sharp directional pencil shaped pattern. Fan-beam pattern − The beam has a fan-shaped pattern. Shaped beam pattern − The beam, which is non-uniform and pattern-less is known as shaped beam. Note: A referential point for all these types of radiation is the isotropic radiation. It is important to consider the isotropic radiation even though it is impractical. Types of Radiation patterns  Radiation pattern Elevation pattern, which represents the The azimuthal plot is a function of the azimuthal angle plot of the radiation pattern as a for a fixed polar angle (90 degrees off the z-axis in this function of the angle measured off the z- case). Since the radiation pattern is symmetrical axis (for a fixed azimuth angle) around the z-axis, this plot appears as a constant. Lobe Formation Radiation pattern indicates major and minor radiation areas, by which radiation efficiency of the antenna is known.  Sidelobe Levels In the transmit mode: Wasted radiated power In the receive mode : Receive from undesired directions Example A radar for detecting low flying aircraft targets can receive strong ground echoes (clutter) through the side lobes which mask the weaker echoes coming from low radar cross-section targets through the main beam.. The optimum compromise (tradeoff) between sidelobes, gain, and beamwidth is an important consideration for choosing or designing radar antennas Lobe Formation Here, the radiation pattern has main lobe, side lobes and back lobe. The major part of the radiated field, which covers a larger area, is the main lobe or major lobe. This is the portion where maximum radiated energy exists. The direction of this lobe indicates the directivity of the antenna. The other parts of the pattern where the radiation is distributed side wards are known as side lobes or minor lobes. These are the areas where the power is wasted. There is other lobe, which is exactly opposite to the direction of main lobe. It is known as back lobe, which is also a minor lobe. A considerable amount of energy is wasted even here.  If the radiated power is calculated by taking half-wave dipole as the reference, rather than an isotropic antenna, then it can be termed as ERP (Effective Radiated Power). ERP (dBW)=EIRP (dBW)− 2.15 dBi dB- DeciBels at 1 Milliwatt Beam width is the aperture angle from where most of the power is radiated. The two main considerations of this beam width are half power beam width (HPBW) and first null beam width (FNBW).  The angular separation, in which the magnitude of the radiation pattern decreases by 50% (or -3dB) from the peak of the main beam, is the Half Power Beam Width.”  “The angular span between the first pattern nulls adjacent to the main lobe, is called as the First Null Beam Width.”  Class Activity Problem # 1 Find the HPBW of an antenna having E() = cos2  for 0o <  < 90o  (HPBW) Problem # 1 Find the (HPBW) of an antenna having E() = cos2  for 0o <  < 90o Solution E() at half power 0.707 = cos2   = 33o BW = 66o Problem Problem Solution Problem Solution Problem Solution Problem An antenna has a gain of 14 dB. It is fed by an RG- 8/U transmission line 250 ft long whose attenuation is 3.6 dB/100 ft at 220 MHz. The transmitter output is 50 W. Calculate (a) the transmission line loss and (b) the effective radiated power. Problem - Solution An antenna has a gain of 14 dB. It is fed by an RG-8/U transmission line 250 ft long whose attenuation is 3.6 dB/100 ft at 220 MHz. The transmitter output is 50 W. Calculate (a) the transmission line loss and (b) the effective radiated power. Polarization. Polarization refers to the orientation of magnetic and electric fields with respect to the earth. If an electric field is parallel to the earth, the electromagnetic wave is said to be horizontally polarized; if the electric field is perpendicular to the earth, the wave is vertically polarized. Antennas that are horizontal to the earth produce horizontal polarization, and antennas that are vertical to the earth produce vertical polarization. Some antennas produce circular polarization, in which the electric and magnetic fields rotate as they leave the antenna. For optimal transmission and reception, the transmitting and receiving antennas must both be of the same polarization. Theoretically, a vertically polarized wave will produce 0 V in a horizontal antenna and vice versa. Polarization. But during transmission over long distances, the polarization of waves changes slightly because of the various propagation effects in free space. Thus even when the polarization of the transmitting and receiving antennas is not matched, a signal is usually received. A vertical or horizontal antenna can receive circular polarized signals, but the signal strength is reduced. When circular polarization is used at both transmitter and receiver, both must use either left- or right-hand polarization if the signal is to be received.  Polarization Defined relative to the E-field of antenna. Horizontally Polarized (If the E-field is horizontal) Vertically Polarized (If the E-field is vertical) Many existing radar antennas are linearly polarized, usually either vertically or horizontally; although these designations indicate an earth reference, they are quite common even for airborne or satellite antennas Co-Polarization and Cross- Polarization Co-polarized antenna pattern Co-Polarization XPD The desired polarization (the Relative Power main polarization) (COPOL) Cross-Polarization The undesired orthogonal polarization (CROSSPOL). X-polarized patttern Azimuth Angle A well-designed antenna will have CROSSPOL components at least 20 dB below the COPOL in the main-beam region, and 5 to 10 dB below in the side lobe regions. Consider the antenna with following radiation pattern, calculate the following. 1.What is the beam-width of this directional antenna? 2.What is the side-lobe level? 3.What is the front-to-back ratio? 4.Will a station transmitting bearing 90° interfere with this pattern? Will this pattern interfere with it? 5.Will a station bearing 240° be able to spy on this communications? Problem Consider the antenna with following radiation pattern, calculate the following. 1.What is the beam-width of this directional antenna? Beam-width = 40° 2.What is the side-lobe level? SLLdB = Gmainlobe (dB) – Gsidelobe(dB) = 0 dB – (−11 dB) = 11 dB 3.What is the front-to-back ratio? FBRdB = Gmainlobe (dB) – Gbacklobe(dB) = 0 dB – (−7 dB) = 7 dB Consider the antenna with following radiation pattern, calculate the following. 4.Will a station transmitting bearing 90° interfere with this pattern? Will this pattern interfere with it? No interference; No side-lobes in that direction. 5.Will a station bearing 240° be able to spy on this communications? Yes, it is possible; This antenna does have a side-lobe in the 240° direction. 2 -D Radiation Pattern of Antenna 3 -D Radiation Pattern of Antenna Isotropic Antenna : A theoretical antenna used as a reference for antenna gain This antennas has no gain in any direction Directivity of an antenna It is the ratio of radiation density in the direction of maximum radiation to the radiation density averaged over all the directions.  Find the gain in dB of a parabolic reflector antenna at 15 GHz having diameter of 1m. Assume efficiency is 0.6. What will be its gain at 36 GHz?  Find the gain in dB of a parabolic reflector antenna at 15 GHz having diameter of 1m. Assume efficiency is 0.6. What will be its gain at 36 GHz?  Find the gain in dB of a parabolic reflector antenna at 15 GHz having diameter of 1m. Assume efficiency is 0.6. What will be its gain at 36 GHz? Solution Aperture Area of parabolic reflector antenna = π r 2 D = 24,674.011 G = 41.7 dB  Find the gain in dB of a parabolic reflector antenna at 15 GHz having diameter of 1m. Assume efficiency is 0.6. What will be its gain at 36 GHz? Solution Aperture Area of parabolic reflector antenna = π r 2 D = 24,674.011 G = 41.7 dB  A radio station has an EIRP of 25 kW and a transmit power of 1.73 kW. What is the gain of the antenna?  A radio station has an EIRP of 25 kW and a transmit power of 1.73 kW. What is the gain of the antenna? EIRP = Pt Gt Gt = EIRP / Pt = 25 kW / 1.73 kW = 14.45  An antenna has a power gain of 800. What will be decibel power gain of this antenna? BIBLIOGRAPHY  Text Books: 1. John D. Kraus and Ronald J. Marhefka and Ahmad S.Khan, ―Antennas and wave propagation,‖ TMH, New Delhi, 4th Ed., (special Indian Edition), 2010. 2. E.C. Jordan and K.G. Balmain, ―Electromagnetic Waves and Radiating Systems,‖ PHI, 2nd Edn, 2000.  Reference Books: 1. C.A. Balanis, ―Antenna Theory- Analysis and Design,‖ John Wiley & Sons, 2nd Edn., 2001. 2. K.D. Prasad, Satya Prakashan, ―Antennas and Wave Propagation,‖ Tech. India Publications, New Delhi, 2001. 3. E.V.D. Glazier and H.R.L. Lamont, ―Transmission and Propagation - The Services Text Book of Radio,‖ vol. 5, Standard Publishers Distributors, Delhi. 4. F.E. Terman, ―Electronic and Radio Engineering,‖ McGraw-Hill, 4th edition, 1955. 5. John D. Kraus, ―Antennas,‖ McGraw-Hill (International Edition), 2nd Edn., 1988.