micro wave comunication slides, easy to learn

7/30/2019 Micro Wave Comunication Slides, Easy to Learn

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by

Lotis P. Patunob, M.Eng., ECE


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Microwaves

An electromagnetic waves with frequencies that ranges

from approximately 500 MHz to 300 GHz or more. And

its wavelengths fall between 1cm and 60 cm.

Wavelength

The distance between

repeating units of apropagating wave of a

given frequency.

Designated by lambda

().


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Categories of Microwave Systems:

A. Short haul used to carry information for relatively

short distances, e.i. between cities within the same state.


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Categories of Microwave Systems:

A. Long haul used to carry information for relatively

long distances, such as interstate.


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Advantages of Microwave Radio:

1. Radio systems do not require a right-of-way

acquisition between stations.

2. Each station requires the purchase or lease of only asmall area of land.

3. Because of their high operating frequencies,

microwave radio systems can carry large quantities of

information.

4. Short wavelengths, require relatively small antennas.

5. Radio signals are more easily propagated around

physical obstacles, such as high mountains


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Disadvantages of Microwave Radio:

1. It is more difficult to analyze and design circuits at

microwave frequencies.

2. Measuring techniques are more difficult to perfectand implement at microwave frequencies.

3. It is difficult to implement conventional circuit

components at microwave frequencies.

4. Transient time is more critical at microwave

frequencies.

5. Microwave frequencies propagate in a straight line,

which limits their use to line-of-sight applications.


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Applications of Microwave:

1. Telephone communications.

2. Radar

3. Space Communications

4. Heating


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Microwave Parameters:

It is the loss that would be obtained between two

isotropic antennas in free space, where there are noground influences or obstructions.

A. Free Space Path Loss, LFS

It is defined as a loss incurred by an electromagnetic

wave as it propagates in a straight line through a

vacuum with no absorption or reflection of energy fromnearby objects.


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Note: signal strength is 1/

distance; & antenna gain

aperture.

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dFSL

)(10)(10 log20log204.32 kmMHz dfFSL

)(10)(10 log20log204.92 kmGHz dfFSL

)(10)(10 log20log206.36 miMHz dfFSL

)(10)(10 log20log206.96 miGHz dfFSL


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General Equation:

B. Parabolic Antenna Gain, G

where: D = antenna diameter in m

= signal wavelength in m

= efficiency

2

DG


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Antenna Gain for Typical Values of (0.55 to 0.75):

Parabolic Antenna Gain for Typical Values of (0.55

to 0.75) in Metric system:

2

6

D

G

)(10)(10 log20log204.42 mMHz DfG

)(10)(10 log20log208.17 mGHz DfG


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Parabolic Antenna Gain for Typical Values of (0.55

to 0.75) in English system:

)(10)(10 log20log206.52 ftMHz DfG

)(10)(10log20log205.7

ftGHzDfG


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C. Fade Margin, FM

It is an attenuation allowance so that anticipated

fading will still keep the signal above specified

minimum RF input.

It considers the nonideal and less predictable

characteristics of a radio wave propagation such as

multipath propagation and terrain sensitivity.


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Fade Margin in Metric system:

)1(log10)6(log10log3013010)(10)(10

RabfdFMMHzkm

)1(log10)6(log10log307010)(10)(10

RabfdFMGHzkm

Fade Margin in English system:

)1(log10)6(log10log308.123 10)(10)(10 RabfdFM MHzmi

)1(log10)6(log10log308.6310)(10)(10

RabfdFMGHzmi


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where: R = propagation reliability

Values for a Description

4.0 for very smooth terrain,

over water, flat desert

1.0 for average terrain with

some roughness

0.25 for mountainous, very

rough, or very dry terrain


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Values for b Description

0.50 for hot, humid coastal areas

0.25 for normal, interior

temperate or sub-arctic area

0.125 for mountainous, very drybut non-reflective areas


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D. System Reliability Estimates

D.1. Propagation Reliability for Non-diversity Systems:

%1001 xUndpR where: Undp = the path unavailability or

fade probability

10/635.1 10)1025.1( FMxxdabfUndp

where: d = path length in mi

f = frequency in GHz

FM = fade margin in dB


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Diversity

It suggests that there is more than one transmission path

or method of transmission available bet. a transmitter

and a receiver. Its purpose is to increase the reliability of

the system by increasing its availability

Frequency diversity

It simply modulates two different RF carrier frequencies

with the same information. At the destination, both aredemodulated but the one yields the better quality is

selected.


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Space diversity

The output of a transmitter is fed to two or more

antennas that are physically separated by anappreciable number of wavelengths.

Diversity

Receiver diversity

It is using more than one receiver for a single RFchannel.


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D.2. Propagation Reliability for Diversity Systems:

where: Udiv = the path unavailability or

fade probability

where: Idiv = the diversity improvement factor

%100)1( xUdivR

di v

ndp

di v I

UU


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D.3. Equipment Reliability:

where: U = unavailability or probability of outage

where: MTTR = mean time to repair

MTBF = mean time before failure

%100)1( xUR

MTBFMTTRU


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E. Received Signal Level, RSL

RXRFSTTXLGLGLPRSL dBmo )(

It is the difference from the nominal transmitter

output, antenna transmit and receive gain, from thatof the fixed losses of transmit and receive side and its

path loss.

where: LTX and LRX = transmitter and receiver

total insertion losses in dB

GT and GR = transmit and receive antenna

gains in dB


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RSL = FM + Threshold (receiver)

where:

FM = Fade Margin in dB

Threshold (receiver) = receiver minimum RF

input in dBm; Cmin

where: LFS = Free Space Loss in dB

Po(dBm) = Transmitter Output Power in dBm

KTBN;min NN

CC


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F. System Gain, Gs (dB)

It is the difference between the nominal output power

of a transmitter and the minimum rf input power to areceiver.

)()()( .min dBmdBmodBS inputRFPG

gainslossesPdBmo

(dBm))(

inputRF.min


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)()()()()()( dBRdBTdBbdBfdBFSdBdBs GGLLLFMG

where: Lf(dB) = transmission line loss bet. thedistribution network and

its respective antenna (dB)

Lb(dB) = total coupling or branching loss

in the distribution network bet.the output of a transmitter or

receiver and the transmission line

(dB)


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G. Fresnel Zone and Fresnel Radius

Fresnel zone the area where the interference is

constructive.


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If a reflected signal is bounced within an odd-

numbered Fresnel zone, it would arrive at the receiver

in phaseaddition with the direct signal.

G. Fresnel Zone and Fresnel Radius


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Fresnel zones are a series of concentric ellipsoids that

surround the path from the transmitter to the receiver.

)()(

)(2)(1)(1 1.547

kmMHz

kmkmm

Df

ddF

Fresnel zone radius, (F1)

in Metric System:

)()(

)(2)(1

)(1 3.17kmMHz

kmkmm

Df

ddF


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)()(

)(2)(1

)(1 2280

miMHz

mimi

ft

Df

ddF

Fresnel zone radius, (F1) in English System:

)()(

)(2)(1)(1 1.72

miGHz

mimift

Df

ddF

nFFn 1nth Fresnel zone radius (Fn):

Fresnel zone clearance (Fc)- it takes into account the

unusual conditions that

occur in the atmosphere.

16.0 FFc


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H. Passive Repeater

Gain of a Passive Repeater

2)(cos4

log20

A

G dBp

where: A = the actual area of the passive repeater in (ft2 )

= wavelength = c/f in (ft)

= alpha, the angle bet. the incident wave and the

reflected wave in ()


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I. Net Path Loss, NPL:

It is the total loss of the system.

RFSpFSTdB GLGLGNPL 21)(

Example:

A plane passive reflector 10x16 ft is erected

21 miles from one active site and only 1 mile from

the other and = 50. The operating frequency is2000 MHz. Determine the net path loss of the

system.


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Example:

In a microwave communication system with a

normal temperate and average terrain has the

following parameters:

a. Operating frequency = 4 GHzb. Path length = 25 mi

c. Tx/Rx antenna diameter = 3 ft.

d. Transmitter Output Power = 1 W

e. Threshold(receiver) = - 80 dBmf. Tx total insertion loss = 5 dB

g. Rx total insertion loss = 4 dB

Deermine: LFS(dB) , FM(dB) & % Reliability


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Waveguides

It is a conducting tube through which the energy is

transmitted, in the form of electromagnetic waves.

It is an alternative to cable for frequency of 1 Ghz andabove.


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Electromagnetic Wave

It is made up of magnetic and electric fields that are at

right angles to each other and at right angles to the

direction of propagation. It travels in a straight line at

approximately the speed of light.


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Modes of Propagation - the possible direction of

distribution of energy

1. Transverse Electric (TE) has the electric field

transverse the direction of propagation, while the

magnetic field is along the propagation direction

2. Transverse Magnetic (TM0) has the magnetic field atright angles to the direction of propagation along the

guide, and the electric field in the direction of

propagation.

Classification of Modes of Propagation:


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Format: TEm,n

where: n = indicates the no. of half wave variation

of the electric field along the y or b

(height) dimension.

m = indicates the no. of half wave variation

of the electric field along the x or a

(width) dimension.


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where: arrows = represent the E field perpendicular to

the sides of the guide.

xs = represent the H field that is going into

the waveguide.

dots = represent the H field that is coming out

of the waveguide.


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Types of Waveguides:

A. Rectangular used when energy must be coupled

from the source to a load and both are fixed in place

since they are smaller than circular waveguides for a

given wavelength.

General formula for

cut off wavelength, c:

22

2

y

n

x

m

c

Cut off wavelength for

TEm,0:

m

x

c

2


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Cut off wavelength for TE1,0:

xc

2

where: TE1,0 = called the dominant mode, the mode for

the lowest frequency that can be

propagated in a waveguide

x = the width of the waveguide

y = the height of the waveguide

Note: x /2 for dominant mode means no propagation


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B. Circular used for rotating systems such as radar

antenna

K

r

c

2

where: K = 1.84 for dominant mode

Example:

What is the cut off wavelength that a 2.5 cm widewaveguide will support the dominant mode (m = 1)?

How about for the next mode (m = 2)?


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Key wavelength formula for rectangular/circularwaveguide:

Rectangular Circular

Cut off wavelength 2x 3.41r

Longest transmitted

with little attenuation

1.6x 3.2r

Shortest before next

mode is possible

1.1x 2.8r


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Group Velocity, Vg

The actual speed at which

a signal travels down the

guide.

2

1

ccg VV

Phase Velocity, Vp

The rate at which the

wave appears to move

along the wall of theguide.

2

1

c

cp

VV

Note: VgVp = Vc2


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Waveguide Characteristic Impedance:

TE mode:

20

1

377

c

Z

TM mode:

20

1

377

c

Z

Example:

A 6 GHz signal is to be propagated in a waveguidewhose width is 7.5 cm. Calculate the characteristic

impedance for TE1,0 mode and TM1,1 mode if the

thickness is 3.75 cm.


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Example:

A 6 GHz signal is to be propagated in the dominant

mode in a rectangular waveguide if its group velocity

is to be 90% of the speed of light, what must be width

of the guide?


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