Post on 08-Nov-2015
description
III. Spherical Waves and RadiationAntennas radiate spherical waves into free spaceReceiving antennas, reciprocity, path gain and path lossNoise as a limit to receptionRay model for antennas above a plane earth and in a street canyonCylindrical waves
2002 by H. L. Bertoni
Radio Channel Encompasses Cables, Antennas and Environment Between Transmitter impresses information onto the voltage of a high power RF carrier for transmission through the air - called modulationReceiver extracts the information from the voltage of a low power received signal - called demodulation
2002 by H. L. Bertoni
Examples of Different Cellular Antennas
2002 by H. L. Bertoni
PCS Antennas
2002 by H. L. Bertoni
Base Station Antennas
2002 by H. L. Bertoni
Antennas Radiate Electromagnetic WavesEM waves have:Electric field E (V/m)Magnetic field H (A/m)E and HPerpendicular to each other and to direction of propagation - PolarizationAmplitude depends on direction of propagation - Radiation PatternTransmitting AntennaEH
2002 by H. L. Bertoni
Spherical Waves Radiated by AntennasI: terminal CurrentZ: constant with units of ohms: 120Radial Power Flux
Antenna pattern = For large r, localized current sources radiate fields in the form of Spherical Wavesz
2002 by H. L. Bertoni
Power Radiation Pattern Power density radiated by antenna P(q) = ExH* watts/m2Poynting vector in the radial directionP(q)q
2002 by H. L. Bertoni
Omnidirectional Antennas
2002 by H. L. Bertoni
Parabolic Reflector Antenna
2002 by H. L. Bertoni
Horn Antennas
2002 by H. L. Bertoni
Log Periodic Dipole Array
2002 by H. L. Bertoni
Dual Polarization Patch Antenna
2002 by H. L. Bertoni
Total Radiated PowerPT is independent of r, as required byconservation of power.
Normalization for is:
2002 by H. L. Bertoni
Antenna Gain and Radiation Resistance for No Resistive LossDirective gain = g(q,f)= |f (q,f)|2 andAntenna gain = G = Max. value of g(q,f)If isotropic antennas could exist, then |f (q,f)|2 = 1, G = 1
Radiation Resistance Rr = effective resistance seen at antenna terminals
2002 by H. L. Bertoni
Antenna Directivity, Gain, Efficiency
2002 by H. L. Bertoni
Short (Hertzian) Dipole Antenna
2002 by H. L. Bertoni
Half Wave Dipole AntennaThe radiated field can be written:
2002 by H. L. Bertoni
Summary of Antenna RadiationRadiation in free space takes the form of spherical wavesE, H and r form a right hand systemField amplitudes vary as 1/r to conserve powerPower varies as 1/r2, and varies with direction from the antennaDirection dependence gives the directivity and gain of the antennaRadiation resistance is the terminal representation of the radiated power
2002 by H. L. Bertoni
Receiving Antennas and ReciprocityFor a linear two-port V1 =Z11I1 + Z12I2 V2 =Z21I1 + Z22I2Reciprocity Z12 = Z21If I2 = 0, V2 = Z12I1 ~ 1/r
For r large,
|Z12|
Circuit Relation for Radiation into Free Space
2002 by H. L. Bertoni
Received Power and Path Loss RatioI2
2002 by H. L. Bertoni
Effective Area of Receiving AntennaEffective Area = Ae
2002 by H. L. Bertoni
Effective Area for a Hertzian DipoleFor matched termination
2002 by H. L. Bertoni
Effective Area for a Hertzian Dipole - cont.
2002 by H. L. Bertoni
Path Gain and Path Loss in Free Space
2002 by H. L. Bertoni
Path Gain in dB for Antennas in Free Space
2002 by H. L. Bertoni
Summary of Antennas as ReceiversDirective properties of antennas is the same for reception and transmissionEffective area for reception Ae = gl2/4pFor matched terminations, same power is received no matter which antenna is the transmitterPath gain PG = PR/PT < 1Path loss PL = 1/PG > 1
2002 by H. L. Bertoni
Noise Limit on Received PowerMinimum power for reception set by noise and interferenceNoise power set by temperature T, Boltzmans constant k and bandwidth Df of receiver: N = kTDf For analog system, received power PR must be at least 10N For digital systems, the maximum capacity C (bits/s) in presence of white noise is given by the limit
2002 by H. L. Bertoni
Sources of Thermal Noise
2002 by H. L. Bertoni
Thermal Noise Power N
Boltsmans constant = k =1.38x10-23 watts/(Hz oK)System temperature = TS oKBandwidth = Df HzFor TS = 300o K and Df = 30x103 HzN = 1.24x10-16 watts(N)dB = -159.1 dBw = -129.1 dBmNoise figure of receiver amplifier F ~ 5 dBEffective noise = N + FFor the example, N + F = -124.1 dBm
2002 by H. L. Bertoni
WalkAbout Phones
Frequency band450 MHz = 0.667 mBand width12.5 kHzThermal noise 4x10-18 mW /Hz5x10-14 mW-133 dBmReceiver noise figure5 dB typicalSNR for reception10 dB for FMMinimum received power2x10-12 mW-118 dBmTransmitted power500 mW27 dBmMaximum allowed path loss(PTr)dB - (PRec)dB145 dBMinimum path gainPRec /PTr = 10-14.53.2x10-15Antenna gain / Antenna heightAssume 0 dB1.6 m
2002 by H. L. Bertoni
Maximum Range WalkAbouts in Free Space
2002 by H. L. Bertoni
Summary of NoiseNoise and interference set the limit on the minimum received power for signal detectionThermal noise can be generated in all parts of the communications systemMiracle of radio is that signals ~ 10-12 mW can be detected
2002 by H. L. Bertoni
Ground and Buildings Influence Radio PropagationReflection and transmission at ground, wallsDiffraction at building corners and edgesDiffraction PathTransmission Reflection
2002 by H. L. Bertoni
Two Ray Model for Antennas Over Flat Earth(Antennas are Assumed to be Isotropic)
2002 by H. L. Bertoni
Reflection Coefficients at Plane Earth Vertical (TM) and Horizontal (TE) Polarizations
2002 by H. L. Bertoni
Path Gain vs. Antenna Separation(h1 = 8.7 m and h2 = 1.8 m)
2002 by H. L. Bertoni
Sherman Island/Rural
2002 by H. L. Bertoni
Sherman Island Measurements vs. Theory
2002 by H. L. Bertoni
Flat Earth Path Loss Dependence for Large R
2002 by H. L. Bertoni
Path Gain of Two Ray Model
2002 by H. L. Bertoni
Maximum Range for WalkAbouts on Flat Earth
2002 by H. L. Bertoni
Fresnel Zone Gives Region of PropagationFresnel zone is ellipsoid about ray connecting source and receiver and such that r2-r1 =l/2Ray fields propagates within Fresnel zoneObjects placed outside Fresnel zone generate new rays, but have only small effect on direct ray fieldsObjects placed inside Fresnel zone change field of direct ray
2002 by H. L. Bertoni
Fresnel Zone Interpretation of Break Point
2002 by H. L. Bertoni
Regression Fits to the 2-Ray Model on Either Side of the Break Point
2002 by H. L. Bertoni
Six Ray Model to Account for ReflectionsFrom Buildings Along the StreetEach ray seen from above represents two rayswhen viewed from the side:
1. Ray propagating directly from Tx to Rx2. Ray reflected from ground
2002 by H. L. Bertoni
Six Ray Model of the Street Canyon
2002 by H. L. Bertoni
Six Ray Model for Street Canyonf = 900 MHz, h1= 10 m, h2= 1.8 m, w = 30 m, zT = zR = 8 m
2002 by H. L. Bertoni
Received Signal on LOS Route f = 1937 MHz, hBS= 3.2 m, hm = 1.6 mTelesis Technology Laboratories, Experimental License Progress Report to the FCC, August, 1991.
2002 by H. L. Bertoni
Summary of Ray Models forLine-of-Sight (LOS) ConditionsRay models describes ground reflection for antennas above the earthPresence of earth changes the range dependence from 1/R2 to 1/R4 Propagation in a street canyon causes fluctuations on top of the two ray modelFresnel zone identifies the region in space through which fields propagate
2002 by H. L. Bertoni
Cylindrical Waves Due to Line Source
2002 by H. L. Bertoni