radar

1. Fundamentals of Microwave
Technologies

2. Historical Perspective
 Founded during WWII.
 Used for long-haul telecommunications.
 Displaced by fiber optic networks.
 Still viable for right-of-way bypass and
geographic obstruction avoidance.

3. Wireless Transmission
 Transmission and reception are achieved
by means of an antenna .
 Directional :
 Transmitting antenna puts out focused
beam .
 Transmitter and receiver must be
aligned .
 Omnidirectional “Isotropically” :
 Signal spreads out in all directions .
 Can be received by many antennas .

4. Wireless Examples
 Terrestrial microwave transmission .
 Satellite transmission .
 Broadcast radio .
 Infrared .

5. Terrestrial Microwave
 Used for long-distance telephone service .
 Uses radio frequency spectrum, from 2 to 40
GHz .
 Parabolic dish transmitter, mounted high .
 Used by common carriers as well as private
networks .
 Requires unobstructed line of sight between
source and receiver .
 Curvature of the earth requires stations
(repeaters) ~30 miles apart .

6. Microwave Applications
 Television distribution .
 Long-distance telephone transmission .
 Private business networks .

7. Microwave
 Advantages :
 No cabling needed between sites .
 Wide bandwidth .
 Multichannel transmissions .
 Disadvantages :
 Line of sight requirement .
 Expensive towers and repeaters .
 Subject to interference -e.g. passing airplanes,
rain .

8. Satellite Microwave Transmission
 A microwave relay station in space .
 Can relay signals over long distances .

9. Wireless Technologies
Microwave
 Microwave systems transmit voice and data through the atmosphere as
super-high-frequency radio waves
 One particular characteristic of the microwave system is that it cannot bend
around corners; therefore microwave antennas must be in "line of sight" of
each other
 The following are some of the characteristics of the microwave system:
1. High Volume
2. Long distance transmission
3. Point to point transmission
4. High frequency radio signals are transmitted from one terrestrial transmitter
to another
5. Satellites serve as a relay station for transmitting microwave signals over
very long distances. See image next slide

10. Wireless Technologies
Low-Orbit Satellite and Microwave
Transmission

11. Microwave Spectrum
 Range is approximately 1 GHz
to 40 GHz
 Total of all usable frequencies under
1 GHz gives a reference on the
capacity of in the microwave range.

12. Microwave Impairments
 Equipment, antenna, and waveguide
failures.
 Fading and distortion from multipath
reflections.
 Absorption from rain, fog, and other
atmospheric conditions.
 Interference from other frequencies.

13. Microwave Engineering
Considerations
 Free space & atmospheric attenuation.
 Reflections.
 Diffractions.
 Rain attenuation.

14.  Skin affect
 Line of Sight (LOS)
 Fading
 Range
 Interference
Microwave Engineering
Considerations

15. Free Space & Atmospheric
Attenuation
 Free space & atmospheric attenuation is
defined by the loss the signal undergoes
traveling through the atmosphere.
Changes in air density and absorption by
atmospheric particles.

16. Reflections
 Reflections can occur as the microwave
signal traverses a body of water or fog
bank; cause multipath conditions

17. Diffraction
 Diffraction is the result of variations in
the terrain the signal crosses

18. Rain Attenuation
 Raindrop absorption or scattering of the
microwave signal can cause signal loss
in transmissions.

19. Skin Affect
 Skin Affect is the concept that high
frequency energy travels only on the
outside skin of a conductor and does
not penetrate into it any great distance.
Skin Affect determines the properties of
microwave signals.

20. Line of Sight
Fresnel Zone Clearance
 Fresnel Zone Clearance is the minimum
clearance over obstacles that the signal
needs to be sent over. Reflection or
path bending will occur if the clearance
is not sufficient.

21. LOS & FZC-cont’d
Fresnel Zone
D1
D2
72.2
D1 X D2
F x D
secret formula

22. Microwave Fading
Normal Signal
Reflective Path
Caused by multi-path reflections and heavy rains

23. Range
 The distance a signal travels and its
increase in frequency are inversely
proportional.
 Repeaters extend range:
 Back-to-back antennas.
 Reflectors.

24. Range-cont’d
 High frequencies are repeated/received
at or below one mile.
 Lower frequencies can travel up to 100
miles but 25-30 miles is the typical
placement for repeaters.

25. Interference
 Adjacent Channel Interference.
 Digital not greatly affected.
 Overreach
 Caused by signal feeding past a repeater
to the receiving antenna at the next station
in the route. Eliminated by zigzag path
alignment or alternate frequency use
between adjacent stations.

26. Components of a Microwave
System
 Digital Modem.
 Radio Frequency (RF) Unit.
 Antenna.

27. Digital Modem
 The digital modem modulates the
information signal (intermediate
frequency or IF).

28. RF Unit
 IF is fed to the RF unit which is
mounted as close physically to the
antenna as possible (direct connect is
optimal).

29. Antenna
 The antenna is a passive device that
radiates the modulated signal. It is fed
by direct connect of the RF unit, coaxial
cable, or waveguides at higher
frequencies.

30. Waveguides
Waveguides are hollow channels of
low-loss material used to direct the
signal from the RF unit to the
antenna.

31. Modulation Methods
 Primarily modulated today with digital
FM or AM signals.
 Digital signal remains quiet until failure
threshold bit error rate renders it unusable.

32. Bit Error Rate (BER)
 The BER is a performance measure of
microwave signaling throughput
 10 or one error per million transmitted bits
of information.
 Data fail over is at 10 ; voice traffic can
withstand this error rate.

33. Diversity
 Space Diversity
 Frequency Diversity
 Hot Standby
 PRI

34. Space Diversity
Normal Signal
Faded Signal
Transmitter Receiver

35. Space Diversity-cont’d
 Space Diversity protects against multi-
path fading by automatic switch over to
another antenna place below the
primary antenna. This is done at the
BER failure point or signal strength
attenuation point to the secondary
antenna that is receiving the transmitted
signal at a stronger power rating.

36. Frequency Diversity
Receiver
Active XTMR
Frequency #1
Protect XTMR
Frequency #2
RCVR
Frequency #1
RCVR
Frequency #2
Transmitter

37. Frequency Diversity-cont’d
 Frequency Diversity uses separate
frequencies (dual transmit and receive
systems); it monitors primary for fail
over and switches to standby.
Interference usually affects only one
range of frequencies. Not allowed in
non-carrier applications because of
spectrum scarcity.

38. Hot Standby*
Receiver
System XTMR
Primary #1
System XTMR
Standby #2
failure switch
Active RCVR
#1
Standby RCVR
#2
Transmitter
*Hot standby is designed for equipment failure only

39. PRI
ReceiverTransmitter
Connect to
PRI interface
& PSTN
Connect to
PRI interface
& PSTN
To PSTN To PSTN
System
Transmission
Facilities
System
Receiver
Facilities

40. Availability Formula
Percent Availability equals:
1 – (outage hours/8760 hours per year)
Private microwaves have 99.99% availability

41. Microwave Path Analysis
 Transmitter output power
 Antenna gain
 proportional to the physical characteristics
of the antenna (diameter)
 Free space gain
 Antenna alignment factor
 Unfaded received signal level

42. Microwave Radio Applications