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Terrestrial Microwave

by

K.V.Ramana Rao


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What is Terrestrial Microwave ?

transmission systems consisting of at least tworadio transmitter/receivers (transceivers)connected to high gain antennas (directionalantennas which concentrate electromagnetic orradio wave energy in narrow beams) focused inpairs on each other.

The operation is point-to-point-communicationsare established between two andonly two antennas with line-of-sight visibility.

This can be contrasted to point-to-multipoint systems like broadcast radio ortelevision.


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How Terrestrial Microwave

Transfer and Receive Data Terrestrial microwave communication employs

Earth-based transmitters and receivers to transferand receive data.

The frequencies used are in the low-gigahertzrange, which limits all communications to line-of-sight.

Example of terrestrial microwave equipment -telephone relay towers, which are placed everyfew miles to relay telephone signals cross country.


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Antenna That Use to Transfer

Data Microwave transmissions typically use a parabolic

antenna that produces a narrow, highly directional

signal. A similar antenna at the receiving site is sensitive

to signals only within a narrow focus.

Because the transmitter and receiver are highly

focused, they must be adjusted carefully so that

the transmitted signal is aligned with the receiver.


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An Antenna is :

An effective interface between the radio and freespace:

RadioAntenna

Free space

For Terrestrial Communications, antennas must bedirectional:

Radio


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Ga (dBi) = 10 log10h [ 4 p Aa /l2 ]

Where:

Ga = Antenna Directive Gain (Catalog spec)

h = Aperture Efficiency (50-55%)

Aa = Antenna Aperture Area

l = Wavelength (speed of light / frequency)

Formula Parabolic Antenna

Directive Gain


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Typical Parabolic

Antenna Gain in dBiAntenna Diameter

Fr

equency

2 ft

(0.6m)

4 ft

(1.2m)

6 ft

(1.8m)

8 ft

(2.4m)

10 ft

(3.0m)

12 ft

(3.7m)

15 ft

(4.5m)

2 GHz 19.5 25.5 29.1 31.6 33.5 35.1 37

4 GHz 25.5 31.6 35.1 37.6 39.5 41.1 43.1

6 GHz 29.1 35.1 38.6 41.1 43.1 44.6 46.6

8 GHz 31.6 37.6 41.1 43.6 45.5 47.1 49.1

11 GHz 34.3 40.4 43.9 46.4 48.3 49.9 51.8

15 GHz 37 43.1 46.6 49.1 51 52.6 NA

18 GHz 38.6 44.6 48.2 50.7 NA NA NA

22 GHz 40.4 46.4 49.9 NA NA NA NA

38 GHz 45.1 51.1 NA NA NA NA NA


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Standard Parabolic Antenna

Basic Antenna

Comprised of Reflector

Feed Assembly

Mount


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Terrestrial Microwave Antennas for

Point-To-Point Communication Terrestrial microwave antennas generate a beam

of RF signal to communicate between twolocations.

Point-To-Point communication depends upon aclear line of sight between two microwaveantennas.

Obstructions, such as buildings, trees or terraininterfere with the signal.

Depending upon the location, usage andfrequency, different types can be utilized.

We will address the basic characteristics of

these various types


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The Use of Microwave Link

A microwave link frequently is used to transmitsignals in instances in which it would beimpractical to run cables.

If you need to connect two networks separated bya public road,

for example, you might find that regulations

restrict you from running cables above or belowthe road. In such a case, a microwave link is anideal solution.


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Ability To Connect With Other

Devices Some LANs operate at microwave frequencies at

low power and use unidirectional transmitters and

receivers. Network hubs can be placed strategically

throughout an organization, and workstations can

be mobile or fixed.

This approach is one way to enable mobile

workstations in an office setting.


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Frequencies That Use By

Terrestrial Microwave In many cases, terrestrial microwave uses

licensed frequencies.

A license must be obtained from the FCC,

and equipment must be installed and

maintained by licensed technicians.


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Frequencies That Use By

Terrestrial Microwave Terrestrial microwave systems operate in the low-

gigahertz range, typically at 4-6 GHz and 21-23GHz, and costs are highly variable depending onrequirements.

Long-distance microwave systems can be quiteexpensive but might be less costly thanalternatives. (A leased telephone circuit, forexample, represents a costly monthly expense.)

When line-of-sight transmission is possible, amicrowave link is a one-time expense that canoffer greater bandwidth than a leased circuit.


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Advantages of Terrestrial

Microwave over Satellite Lower cost

Avoid exorbitant costs of leasing satellites (unless

satellites are already owned by the customer) Reduced latency

Video is delivered with minimal delay. Satellite signals

must travel significantly further with an average delay

of 250 milliseconds for signals to travel to a geo-satellite and return to earth (this excludes video

processing delay).


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Microwave over Satellite Increased Flexibility

BMS terrestrial systems are easily reconfigurable fordifferent power levels and frequencies.

BMS terrestrial systems are mobile and easily deployedwherever coverage is needed. Multiple satellites mayneed to be utilized for all the required coverage areas.

Video can be captured using light weight, mobileequipment in difficult-to-reach areas. Video can alsobe captured by moving aircraft, ships, and vehicles.

Aircraft with BMS digital microwave for line-of-sight(LOS) communications can also be equipped with asatellite tracking antenna for beyond-line-of-sight(BLOS) satellite communications when needed.


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Microwave over Satellite Reduced Size & Weight

The RF link operates over a shorter distance and

requires less power than a satellite equivalent. Lowerpower means less weight, smaller size and reduced

power consumption.

Ground-based systems can use a tracking antenna for

higher gain. Higher antenna gain results in lower

transmit power requirements. This is less practical for

satellite mounted antennas.

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