ron milione ph.d. w2tap w2tap informationmodulatoramplifier ant feedline transmitter...
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Ron Milione Ph.D.Ron Milione Ph.D. W2TAPW2TAP
Information Modulator Amplifier
Ant
Feedline
Transmitter
Information Demodulator Pre-Amplifier
Ant
Feedline
Receiver
Filter
Filter
RF Propagation
This presentation concentrates on the propagation portion
As the wave propagates, the surface area increases The power flux density
decreases proportional to 1/d2
• At great enough distances from the source, a portion of the surface appears as a plane
• The wave may be modeled as a plane wave
• The classic picture of an EM wave is a single ray out of the spherical wave
Most real antennas do not radiate spherically The wavefront will be
only a portion of a sphere
• The surface area of the wave is reduced
• Power density is increased!
• The increase in power density is expressed as Antenna Gain
• dB increase in power along “best” axis
• dBi = gain over isotropic antenna
• dBd = gain over dipole antenna
Gain in this area
Radiated power often referenced to power radiated by an ideal antenna
ttGPEIRP Pt = power of transmitter
Gt = gain of transmitting antenna system
• The isotropic radiator radiates power uniformly in all directions
• Effective Isotropic Radiated Power calculated by:
Gt = 0dB = 1 for isotropic antenna
This formula assumes power and gain is expressed linearly. Alternatively,you can express power and gain in decibels and add them: EIRP = P(dB) + G(dB)
The exact same formulas andprinciples apply on the receiving side too!
22Dd f
• Large-scale (Far Field) propagation model
• Gives power where random environmental effects have been averaged together
• Waves appear to be plane waves
• Far field applies at distances greater than the Fraunhofer distance:
D = largest physical dimension of antenna
= wavelength
• Small-scale (Near Field) model applies for shorter distances
• Power changes rapidly from one area/time to the next
2
2
2
2 )4()4()(
c
fdd
P
PlinlossFree
r
t
For Free Space (no buildings, trees, etc.)
dBdfc
fddBlossFree 56.147log20log20
4log10)( 1010
2
10
f = frequencyd = distance (m)= wavelength (m)c = speed of light
hb = base station antenna height (m)hm = mobile antenna height (m)a(hm) is an adjustment factor for the type of environment and the height of the mobile.
a(hm) = 0 for urban environments with a mobile height of 1.5m.Note: Hata valid only with d in range 1000-20000, hb in range 30-200m
)3)(loglog55.60.44(
)(log82.13)6(log16.2655.69)(
1010
1010
dh
hahfdBlossHata
b
mb
For Urban environments, use the Hata model
A transmission system transmits a signal at 960MHz with a power of 100mW usinga 16cm dipole antenna system with a gain of 2.15dB over an isotropic antenna.At what distance can far-field metrics be used?
= 3.0*108 m/s / 960MHz = 0.3125 meters
Fraunhofer distance = 2 D2/ = 2(0.16m)2/0.3125 = 0.16m
What is the EIRP?
Method 1: Convert power to dBm and add gainPower(dBm) = 10 log10 (100mW / 1mW) = 20dBmEIRP = 20dBm + 2.15dB = 22.15dBm
Method 2: Convert gain to linear scale and multiplyGain(linear) = 102.15dB/10 = 1.64EIRP = 100mW x 1.64 = 164mW
Checking work: 10 log10 (164mW/1mW) = 22.15dBm
A transmission system transmits a signal at 960MHz with a power of 100mW using a 16cm dipole antenna system with a gain of 2.15dB over an isotropic antenna.What is the power received at a distance of 2km (assuming free-space transmission and an isotropic antenna at the receiver)?
Loss(dB) = 20 log10(960MHz) + 20 log10(2000m) – 147.56dB
= 179.6dB + 66.0dB – 147.56dB = 98.0dB Received power(dBm) = EIRP(dB) – loss = 22.15dBm – 98.0dB = -75.85dBmReceived power(W) = EIRP(W)/loss(linear) = 164mW / 1098.0dB/10 = 2.6 x 10-8 mW = 2.6 x 10-11 W Checking work: 10 -75.85dBm/10
= 2.6x 10-8 mW
What is the power received at a distance of 2km (use Hata model with base height 30 m, mobile height 1.5 m, urban env.)?
Loss(dB) = 69.55+26.16(log(f)-6) – 13.82(log(hb)) – a(hm)+ 44.9-6.55(log(hb))(log(d)-3)
=69.55 + 78.01 – 27.79 – 0 + (35.22)(0.30) = 130.34 dB Received power = 22.15dBm – 130.34dB = -108.19dBm
A Link Budget analysis determines if there is enough power at the receiver to recover the information
Information Modulator Amplifier
Ant
Feedline
Transmitter
Information Demodulator Pre-Amplifier
Ant
Feedline
Receiver
Filter
Filter
RF Propagation
Gain
Gain
Loss
Begin with the power output of the transmit amplifier Subtract (in dB) losses due to passive components in the
transmit chain after the amplifier Filter loss Feedline loss Jumpers loss Etc.
Add antenna gain dBi
Result is EIRP
Information Modulator Amplifier
Ant
Feedline
Transmitter
Filter
RF Propagation
dBi12Antenna gain
dB(1.5)150 ft. at 1dB/100 footFeedline loss
dB(1)Jumper loss
dB(0.3)Filter loss
dBm4425 WattsPower Amplifier
ScaleValueComponent
dBm53Total
All values are example values
The Receiver has several gains/losses Specific losses due to known environment around the
receiver Vehicle/building penetration loss
Receiver antenna gain Feedline loss Filter loss
These gains/losses are added to the received signal strength The result must be greater than the receiver’s sensitivity
InformationDemodulatorPre-Amplifier
Ant
Feedline
Receiver
Filter
Sensitivity describes the weakest signal power level that the receiver is able to detect and decode Sensitivity is dependent on the lowest signal-to-noise
ratio at which the signal can be recovered Different modulation and coding schemes have
different minimum SNRs Range: <0 dB to 60 dB
Sensitivity is determined by adding the required SNR to the noise present at the receiver
Noise Sources Thermal noise Noise introduced by the receiver’s pre-amplifier
Thermal noise N = kTB (Watts)
k=1.3803 x 10-23 J/K T = temperature in Kelvin B=receiver bandwidth
Thermal noise is usually very small for reasonable bandwidths
Noise introduced by the receiver pre-amplifier Noise Factor = SNRin/SNRout (positive because
amplifiers always generate noise) May be expressed linearly or in dB
The smaller the sensitivity, the better the receiver
Sensitivity (W) = kTB * NF(linear) * minimum SNR required (linear)
Sensitivity (dBm) =10log10(kTB*1000) + NF(dB) + minimum SNR required (dB)
Example parameters Signal with 200KHz bandwidth at 290K NF for amplifier is 1.2dB or 1.318 (linear) Modulation scheme requires SNR of 15dB or 31.62 (linear)
Sensitivity = Thermal Noise + NF + Required SNR Thermal Noise = kTB =
(1.3803 x 10-23 J/K) (290K)(200KHz) = 8.006 x 10-16 W = -151dBW or -121dBm
Sensitivity (W) = (8.006 x 10-16 W )(1.318)(31.62) = 3.33 x 10-14 W
Sensitivity (dBm) = -121dBm + 1.2dB + 15dB = -104.8dBm Sensitivity decreases when:
Bandwidth increases Temperature increases Amplifier introduces more noise
Transmit/propagate chain produces a received signal has some RSS (Received Signal Strength) EIRP minus path loss For example 50dBm EIRP – 130 dBm = -80dBm
Receiver chain adds/subtracts to this For example, +5dBi antenna gain, 3dB
feedline/filter loss -78dBm signal into receiver’s amplifier
This must be greater than the sensitivity of the receiver If the receiver has sensitivity of -78dBm or lower,
the signal is successfully received.
Information Modulator Amplifier
Ant
Feedline
Transmitter
Information Demodulator Pre-Amplifier
Ant
Feedline
Receiver
Filter
Filter
RF Propagation
EIRP
Prop Loss
RSS
Sensitivity
A Link Budget determines what maximum path loss a system can tolerate Includes all factors for EIRP, path loss, fade margin, and
receiver sensitivity For two-way radio systems, there are two link budgets
Base to mobile (Forward) Mobile to base (Reverse)
The system link budget is limited by the smaller of these two (usually reverse) Otherwise, mobiles on the margin would have only one-
way capability The power of the more powerful direction (usually
forward) is reduced so there is no surplus Saves power and reduces interference with neighbors
Forward (Base to Mobile) Amplifier power 45dBm Filter loss (2dB) Feedline loss (3dB) TX Antenna gain 10dBi Path loss X Fade Margin (5dB) Vehicle Penetration (12dB) RX Antenna gain 3dBi Feedline loss (3dB)
Signal into mobile’s LNA has strength 33dBm – path loss
If Mobile Sensitivity is -100dBm Maximum Path loss = 133dB
• Reverse (Mobile to Base)• Amplifier power
28dBm• Filter loss
(1dB)• Feedline loss
(3dB)• TX Antenna gain
3dBi• Fade Margin
(5dB)• Vehicle Penetration
(12dB)• Path Loss X• RX Antenna gain
10dBi• Feedline loss
(3dB)• Signal into base’s LNA has
strength 17dBm – path loss• If Base Sensitivity is -105dBm
• Maximum Path loss = 122dB
Unbalanced – Forward path can tolerate 11dB more loss (distance) than reverse
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