Chapter 2: Radio Wave Propagation Fundamentals

1 The Research University in the Helmholtz AssociationINSTITUTE OF Radio FREQUENCY ENGINEERING AND ELECTRONICSC hapter 2: Radio Wave Propagation Marwan Younis2 Institute of Radio Frequency Engineering and ElectronicsScope of the (Today s) LectureChapter 2: Radio Wave Propagation and FrequencySelective Radio ChannelAntennasfiltering, amplificationD Asource & channel decodingfiltering, amplificationdemodulationNoiseEffects during wireless transmission of signals: physical phenomenathat influence the Propagation of electromagnetic waves no statistical descriptionof those effects in terms of modulated signals3 Institute of Radio Frequency Engineering and ElectronicsPropagation PhenomenaChapter 2: Radio Wave Propagation Npath 1path ifreespace Propagation :-line of sight-no multipathdiffraction:-knife edge diffractionreflection:-plane wave reflection-Fresnel coefficientsscattering:-rough surface scattering-volume scatteringrefraction in thetroposphere.

2 -not consideredIn general multipath Propagation leads to fading at the receiver site4 Institute of Radio Frequency Engineering and ElectronicsThe ReceivedSignalChapter 2: Radio Wave Propagation fadingsmall-scale fadingFadingis a deviationof the attenuationthat a signal experiences over certain Propagation may vary with time, positionand/or frequencyTimeFrequencySignal fadingClassification of fading: large-scalefading (gradual change in local average of signal level) small-scalefading (rapid variations due to random multipath signals)5 Institute of Radio Frequency Engineering and ElectronicsPropagation ModelsChapter 2: Radio Wave Propagation multipath conditions in urban areas (small-scale fading) Propagation models (PM) are being used to predict: averagesignal strength at a given distance from the transmitter variabilityof the signal strength in close spatial proximity to a particular locationPM can be divided into.

3 Large-scalemodels(mean signal strength for large transmitter receiver separation) small-scalemodels(rapid fluctuations of the received signal over very short travel distances)6 Institute of Radio Frequency Engineering and ElectronicsChapter 2: Radio Wave Propagation PropagationFreeSpace Propagation7 Institute of Radio Frequency Engineering and ElectronicsFree space PropagationChapter 2: Radio Wave Propagation freespace equation:TxRxPtPrGtGrrno (influence of) groundAntenna effective area:Power density at Rx site:Received power:Assumptions: unobstructedline of sight (LOS) no multipathpropagation8 Institute of Radio Frequency Engineering and ElectronicsReceived Power and Path LossChapter 2: Radio Wave Propagation : polarization matched receiving antenna conjugate complex impedance matching of the receiverUsing:Path loss:Isotropic path loss (no antenna gains):ii9 Institute of Radio Frequency Engineering and ElectronicsChapter 2: Radio Wave Propagation of Field Vectors and Reference Planes10 Institute of Radio Frequency Engineering and ElectronicsPolarization of the EM WavesChapter 2.

4 Radio Wave Propagation ellipticallypolarized EM wave can be decomposedinto a horizontaland a verticalcomponent. LinearCircularElliptical11 Institute of Radio Frequency Engineering and ElectronicsPolarization: II, , V or H? Chapter 2: Radio Wave Propagation (E-field vector) with respect to the plane of incidence: parallel (II) perpendicular ( )TPolarization (E-field vector) with respect to the earth coordinates: vertical (V) horizontal (H)Plane of incidence:formed by thenormal vectorto the reflecting surfaceand Poynting vectorof the incidence waveEIIor EVEor EHT12 Institute of Radio Frequency Engineering and ElectronicsChapter 2: Radio Wave Propagation and TransmissionDielectric Boundary13 Institute of Radio Frequency Engineering and ElectronicsSnell sLaw of ReflectionChapter 2.

5 Radio Wave Propagation r t surface large compared to the wave length smooth surface(otherwise scattering) three angles:-incidence-reflection-transmissio n / refraction*full derivation in Arthur Schuster: An Introduction to the Theory of Optics 12)sin()sin(nnti Relation between angles through Fermat s principle (principle of least time):- the rays of light (EM-waves) traverse the path of stationary optical length This results in* Snell s laws:- ratio of the sines of the angles of incidence and refractionisequivalent to the opposite ratio of the indices of refraction - the incidence and reflectionangles are equal and they are in the same plane ri xrxrxn,, 14 Institute of Radio Frequency Engineering and ElectronicsWhich Part is Transmitted / Reflected?

6 Chapter 2: Radio Wave Propagation procedure: Definition of the electric field strength of the incident wave Reflected and transmitted field strengths Faraday s law of induction Boundary conditions at the border between two dielectric media Decomposition of the incident waves on parallel and normal components15 Institute of Radio Frequency Engineering and ElectronicsFresnel Reflection & Transmission CoefficientsChapter 2: Radio Wave Propagation :parallelperpendicularFresnel coefficients are frequency dependentand in general complex16 Institute of Radio Frequency Engineering and ElectronicsBrewster s Angle (I) Chapter 2: Radio Wave Propagation , where no reflection occurs is Brewster s Angle: exists only for parallel (II / V) polarization calculation by comparing the reflection coefficient to zero calculation by using physical limitations 17 Institute of Radio Frequency Engineering and ElectronicsBrewster s Angle (II) Chapter 2.

7 Radio Wave Propagation (lessdense)Glass (dense)18 Institute of Radio Frequency Engineering and ElectronicsBrewster s Angle (III) Chapter 2: Radio Wave Propagation in degree19 Institute of Radio Frequency Engineering and ElectronicsBrewster s Angle (IV) Chapter 2: Radio Wave Propagation principle ofBrewster window: used for windows in optical or quasi optical systems window with normal incidence reflection loses at window window tilted at Brewster s angle no reflection loses at windowMicrowave gyrotronBrewster window20 Institute of Radio Frequency Engineering and ElectronicsTotal Internal Reflection(I) Chapter 2: Radio Wave Propagation does the total internal reflection appears?

8 A ray must strike the medium s boundaryat an angle larger than the critical angle calculation by comparing thetransmission angle to 90 degree itcttiinnnntarcsinsinsin90 critical angle exists only for nt< niTotal reflection of red laser light in PMMAI ncreasing the incidence angle21 Institute of Radio Frequency Engineering and ElectronicsTotal Internal Reflection(II) Chapter 2: Radio Wave Propagation principle ofrain sensors: IR-beam projected on the glass-air interface at a specific angle total inner reflection in dry conditions partial transmission to the second medium if windshield is wet reduced receive power triggers the sensorRain sensor in the rear view mirror 22 Institute of Radio Frequency Engineering and ElectronicsVisualization Parallel Pol E-FieldChapter 2: Radio Wave Propagation Pol Air toGlassParallel Pol Glass to Air23 Institute of Radio Frequency Engineering and ElectronicsVisualizationPerpendicularPol E-FieldChapter 2.

9 Radio Wave Propagation Air toGlassPerpendicular Pol Glass to Air24 Institute of Radio Frequency Engineering and ElectronicsChapter 2: Radio Wave Propagation and(no)TransmissionPerfect Electric Conductor (PEC)25 Institute of Radio Frequency Engineering and ElectronicsOrthogonal PEC ReflectionChapter 2: Radio Wave Propagation waveEyHxSreflected waveEyRHxRSRyxzSREyHxEyRHxRBoundary conditions: 0tan,tan,tanriEEE 0,,rnorminormnormHHH26 Institute of Radio Frequency Engineering and ElectronicsPEC Reflection, Orthogonal PolarizationChapter 2: Radio Wave Propagation waveHxiHziHrEyiHiHzrHxrEyrEyHreflected waveaiyxzPEC reflectorai arPlane of incidencePEC reflection: RII= +1 R = -1 (to ensure Etan= 0)TSS27 Institute of Radio Frequency Engineering and ElectronicsPEC Reflection: ApplicationsChapter 2: Radio Wave Propagation calibration with metallic: dihedral trihedral (corner reflector)Reflection in the direction of incidence:Satellite radar calibrationRadar image with corner reflectorsBuoy with dihedral28 Institute of Radio Frequency Engineering and ElectronicsChapter 2.

10 Radio Wave Propagation Model29 Institute of Radio Frequency Engineering and ElectronicsGeometryChapter 2: Radio Wave Propagation model is based on geometrical opticsand predicts large-scale fadingzTzRTRd1d2drjjground( )air ( = )30 Institute of Radio Frequency Engineering and ElectronicsAssumptionsChapter 2: Radio Wave Propagation in two-ray model: ground is PEC d >> zT,zRObservations: the received power PRoscillates like a sin2or cos2with distance the minimum value of PRis 0 the maximum value of PRis 4 PR,freespace(+ 6 dB)d31 Institute of Radio Frequency Engineering and ElectronicsLarge DistancesChapter 2: Radio Wave Propagation : d >> k0zTzR cos2x 1 sin2x x2 Observations: parallel pol: 20 dB / decade, perpendicular pol: 40 dB / decade perpendicular pol: independent on frequency perpendicular pol: antenna height gain(double zTor zR quadruplePR)32 Institute of Radio Frequency Engineering and ElectronicsBreakpointChapter 2: Radio Wave Propagation .