BPSU, Philippines - Microwave Link Communication Design aided using Google Earth PDF

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MICROWAVE LINK COMMUNICATION DESIGN INTRODUCTION In today’s information age, knowledge is made readily available not only through cable or wired connections but also through wireless communications. Knowing your way back in the mountains is no longer a problem with GPS (Global Positioning System). C...

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MICROWAVE LINK COMMUNICATION DESIGN

INTRODUCTION In today’s information age, knowledge is made readily available not only through cable or wired connections but also through wireless communications. Knowing your way back in the mountains is no longer a problem with GPS (Global Positioning System). Communicating with family and friends without the use of landline phones is now possible with cellular phones. Exchanging documents can be done in a minute using Bluetooth. Even accessing the internet in a restaurant or while commuting is now a regular thing because of Wi-Fi (Wireless Fidelity). And the one thing they all have in common is that they operate in microwave frequencies.

Microwaves are electromagnetic waves with frequencies that range from approximately 500MHz to 300GHz or more. The prefix "micro-" in "microwave" is not meant to suggest a wavelength in the micrometers range. It only indicates that microwaves are "small" compared to waves used in typical radio broadcasting, falling along 1.0mm to 30cm which are slightly longer than infrared energy.

The main advantage of using microwaves in communications is that it has the capacity to carry thousands of individual information channels between two points without the need for physical facilities such as coaxial cables or optical fibers. It also avoids the need for right-of-way acquisition between properties and are better suited for spanning large bodies of water, going over high mountains, or going through heavily wooded terrain that impose formidable barriers to cable systems. But with these advantages also comes disadvantages. Due to high frequencies employed in microwave systems, it is more difficult to analyze and design circuits and to implement measuring techniques and conventional components. Also, microwave frequencies propagate in a straight line, limiting their use to line-of-sight applications.

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MICROWAVE LINK COMMUNICATION DESIGN Aside from those mentioned earlier, another line-of-sight application for microwaves is a point-to-point communication link. It uses a beam of radio waves in the microwave frequency range to transmit information between two fixed locations on the Earth. A point-to-point microwave communication link is often employed in the form of fixed-link operator, utility private network, TV distribution network and mobile backhaul network among other things.

In the succeeding parts, the group will design a point-to-point microwave communication link with no specific application intended but with communication requirements identified. In this design, the specified points of communication are Dangcol Balanga, Bataan as the receiver site while the transmitter site can be any location at least 25km away from the receiver site. The maximum transmit power is 2W with a receiver IF bandwidth of 10MHz. To meet ―industry standard‖, the performance requirements range per link should be from a minimum of 99.999% availability (about 300seconds outage a year) to 99.9996% (about 125seconds outage a year).

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MICROWAVE LINK COMMUNICATION DESIGN

ACKNOWLEDGMENT The group would like to extend their gratitude and appreciation to the following persons who have shown their support and have been an integral part in the progress and completion of this design.

To Engr. Riadal Sampang, their instructor, for her patience, assistance, and professional guidance in the preparation and completion of this design,

To their family members, for inspiring them to work hard in this project and for understanding and attending to their needs,

To their classmates and friends, for supporting them despite undergoing the same hardships in their own designs,

And above all, to the Almighty God, who bestowed them with intelligence and provide them with the determination to put this design together up to the end.

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MICROWAVE LINK COMMUNICATION DESIGN

TABLE OF CONTENTS INTRODUCTION

1

ACKNOWLEDGMENT

3

TABLE OF CONTENTS

4

OBJECTIVES

5

DESIGN CONSIDERATIONS

6

I SITE SELECTION

6

II ANTENNA HEIGHT

10

III TOWERS IV FIELD SURVEY REPORT V ANTENNA TYPES VI REPEATER VII WAVEGUIDE AND TRANSMISSION LINES

16 22 31 34 36

DESIGN SPECIFICATIONS

40

DESIGN COMPUTATION

41

SYSTEM RELIABILITY

52

SYSTEM FIGURE

53

POWER LEVEL DIAGRAM

55

COST ESTIMATION

56

CONCLUSION

57

GLOSSARY

59

SPECIFICATIONS

60

REFERENCES

69

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MICROWAVE LINK COMMUNICATION DESIGN

OBJECTIVES MAIN OBJECTIVE To design a Point-to-Point Microwave Communication Link with a path length of no less than 25 kilometers from the receiver site (Dangcol, Balanga Bataan) with 4 million pesos (Php 4 000 000) as the allocated budget.

SPECIFIC OBJECTIVES 

Discuss the factors that should be considered in the design of the microwave link.



Select possible receiver, transmitter and if necessary, repeater site locations to provide a path link with line-of-sight (LOS).



Visit site locations to check for land availability and for possible obstructions and their height.



Compute for antenna tower height by considering the effective Earth bulge, land elevation, height of obstructions (e.g. houses, commercial establishments, trees) and Fresnel clearance.



Choose antenna tower based on computed height, land area, and location wind loading.



Choose antenna type and diameter to be used for the transmitting and receiving antennas.



Choose the type of repeater, waveguide and transmission lines to be used.

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MICROWAVE LINK COMMUNICATION DESIGN



Solve for system reliability and figure and provide a power level diagram.



Provide a tabulated list of the materials including description, specification, and cost.

DESIGN CONSIDERATIONS I.

SITE SELECTION Site selection is the process of choosing the optimal location for an anticipated

use. It involves measuring the needs of a new project against the merits of potential locations. Since microwave communication is a line-of-sight (LOS) communication, the first step in choosing the location of the transmitter and receiver sites is verifying that there are no natural and man-made obstructions between them. In cases where a straight path with no obstructions is unavailable, a repeater can be employed to relay signals over the obstructions so that the signal can cover longer distances.

Microwave terminal sites can be a tower constructed on an existing structure such as building rooftops or a separate tower in an elevated location. In putting up a tower on a building rooftop, the architectural and structural plan of the building should be investigated to determine whether the structure is adequate. The cost of building modifications to accomplish the purpose and the possibility of future building construction along the path must also be taken into consideration. When additional height is required and building structure is unable to support a tower, a separate tower can be erected to mount the antenna fixtures.

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MICROWAVE LINK COMMUNICATION DESIGN For maintenance purposes, the site location should have road access from the nearest improved road to the proposed building location. The site should also have adequate source of power often in the form of commercial electric power of suitable secondary or distribution voltage.

Before visiting every potential terminal site, topographic maps are often used to check the terrains for clear LOS. Topographic maps are detailed, accurate graphic representations of features that appear on the Earth’s surface. These features can be divided into the following categories: 

Culture: roads, buildings, urban development, boundaries, railways, power transmission lines



Hydrography: lakes, rivers, streams, swamps, coastal flats



Relief: mountains, valleys, slopes, depressions



Vegetation: wooded and cleared areas, vineyards and orchards



Toponymy: place names, water feature names, highway names

Since topographic maps are only two or three dimensional representation of the physical environment at a given time, it will never be entirely up to date. Therefore, terrain mapping using topographic maps is a good starting point and is only a prerequisite to a field survey.

In the site selection, the group used Google Earth to check for line-of-sight in choosing potential terminal site locations. Google Earth is a virtual globe, map and geographical information program that maps the Earth by the superimposition of images obtained from satellite imagery, aerial photography and geographic information system (GIS) 3D globe. The baseline resolution of Google Earth is about 15 meters while BSECE5B

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MICROWAVE LINK COMMUNICATION DESIGN the altitude resolution varies by country. Since Google Earth is free and is readily available to students, the group used it as a preliminary tool in the site selection.

In this microwave link communication design, the required receiver site is Dangcol Balanga, Bataan. Since there are no buildings of suitable height to construct a tower on, the group chose an empty lot along a concrete road as the receiver site (14°38'49.37"N, 120°29'57.32"E). After establishing the receiver site, the group selected potential transmitter sites that are at least 25km away from the receiver site as per requirement. The chosen transmitter site is in Prado Siongco, Lubao Pampanga. The transmitter site (14°52'23.54"N, 120°31'27.50"E) is also an empty lot (for reasons the same BSECE5B

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MICROWAVE LINK COMMUNICATION DESIGN as the receiver site) about one kilometer away from a concrete road. Since the transmitter and receiver sites have no line-of-sight, a repeater site is also chosen. The repeater site (14°41'25.74"N, 120°29'2.43"E) is also an empty lot along the road in Capitangan, Abucay Bataan. Given that the three sites have road access, it is assumed that transmission power lines also exist especially if there are street lights. The finality of the selected site locations will be verified in a field survey.

RECEIVER SITE TO TRANSMITTER SITE: 25.2km

REPEATER TO TRANSMITTER

REPEATER TO RECEIVER

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MICROWAVE LINK COMMUNICATION DESIGN II.

ANTENNA HEIGHT The antenna height at each end of the link can be determined by creating a path

profile. A path profile is a graphical representation of the path traveled by the radio waves between the two ends of a link. Together with considering the effects of Earth bulge and Fresnel Zones, it insures that the link is free from obstructions.

EARTH BULGE Microwave Propagation at Free Space

Although the surface of the Earth is curved, a beam of microwave energy tends to travel in a straight line. Thus, over some distance, there is a protuberance called the ―physical Earth bulge‖.

Microwave Propagation at Standard Atmospheric Condition

However, since microwaves propagate in air instead of free space, the beam is normally bent downward a slight amount by atmospheric refraction. Any change in the

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MICROWAVE LINK COMMUNICATION DESIGN amount of beam bending caused by atmospheric conditions can then be expressed as a change in k or effective Earth radius factor.

k-factor

ATMOSPHERIC CONDITION Flat Earth Condition: The refractive signal path arc follows earth curvature

k=∞

exactly, meaning there is no relative change in the curvature between the beam and the Earth. This makes the Earth appear ―flat‖. Sub-standard / Sub-refraction Condition: The refracted signal path deviates

2 k3

deviates from a straight line, and it arcs in the same direction as the earth curvature. This results in an effective flattening of the Earth Standard Condition: The usual effect of the declining pressure of the atmosphere with height is to bend radio waves down toward the surface of

4 k=3

4 the Earth by a factor of 3. The end result is that the earth can be considered a little bit flatter. It is a very small variation, but sufficient to help microwave engineers to reach unseen sites.

When the effects of atmospheric refraction are combined with physical Earth bulge, a modified profile is produced, known as ―effective Earth bulge.‖ The formula for effective Earth bulge is given as:

Earth bulge(m) =

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d1(km) x d2(km) 12.75k

Earth bulge(ft) =

d1(mi) x d2(mi) 1.5k

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MICROWAVE LINK COMMUNICATION DESIGN Where: d1 and d2 = the distance from each end site k = the effective Earth radius factor

FRESNEL ZONES

A Fresnel zone, named for physicist Augustin-Jean Fresnel, is one of a (theoretically infinite) number of concentric ellipsoids which define volumes in the radiation pattern of a (usually) circular aperture. Fresnel zones result from diffraction by the circular aperture. The cross section of the first (innermost) Fresnel zone is circular. Subsequent Fresnel zones are annular (doughnut-shaped) in cross section, and concentric with the first.

If unobstructed, radio waves will travel in a straight line from the transmitter to the receiver. But if there are reflective surfaces along the path, such as bodies of water or smooth terrain, the radio waves reflecting off those surfaces may arrive either out of phase or in phase with the signals that travel directly to the receiver. Waves that reflect off of surfaces within an even Fresnel zone are out of phase with the direct-path wave and reduce the power of the received signal. Waves that reflect off of surfaces within an BSECE5B

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MICROWAVE LINK COMMUNICATION DESIGN odd Fresnel zone are in phase with the direct-path wave and can enhance the power of the received signal. Sometimes this results in the counter-intuitive finding that reducing the height of an antenna increases the signal-to-noise ratio.

Fresnel provided a means to calculate where the zones are--where a given obstacle will cause mostly in phase or mostly out of phase reflections between the transmitter and the receiver. Obstacles in the first Fresnel zone will create signals with a path-length phase shift of 0 to 180 degrees, in the second zone they will be 180 to 360 degrees out of phase, and so on. Even numbered zones have the maximum phase cancelling effect and odd numbered zones may actually add to the signal power.

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MICROWAVE LINK COMMUNICATION DESIGN To maximize receiver strength, one needs to minimize the effect of obstruction loss by removing obstacles from the radio frequency line of sight (RF LOS). To establish RF LOS, it is necessary to clear 60% of the 1st Fresnel zone boundary, from the signal beam centerline outwards, across the entire signal path. Failure to do so will result in additional signal loss caused by diffraction; the amount of loss will depend on the degree of Fresnel zone encroachment. The formula for Fresnel zone is:

Fn(m) = 17.3√

Fn(ft) = 72.1√

Where: Fn = Specific Fresnel zone radius d1 = Distance from one end of path to reflection point d2 = Distance from reflection point to opposite end of path D = Total length of path f = Frequency in GHz n = number of specific Fresnel zone

The formula for Fresnel clearance is: Fc = 0.6(F1) Where: F1 = First Fresnel Zone

After choosing tentative terminal sites and determining the relative elevation of the terrain, a path profile is prepared next. The path is created by plotting the Earth BSECE5B

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MICROWAVE LINK COMMUNICATION DESIGN Curvature and the Total Height Extended. The Earth Curvature is the elevation profile of the land with the addition of the effects of the Earth Bulge. The Total Height Extended is the Earth Curvature with the addition of the Fresnel Clearance and 15 meters for vegetation. The initial path link is used to plot a line of sight from the transmitter to repeater and from repeater to receiver.

TRANSMITTER TO REPEATER LINK

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MICROWAVE LINK COMMUNICATION DESIGN REPEATER TO RECEIVER LINK

The red triangle in the plot is a representation of the antenna height. The antenna height is calculated by subtracting the Total Height Extended from the Earth’s Elevation. The tentative antenna height for the transmitter, receiver, and repeater (both in Transmitter-Repeater Link and Receiver-Repeater Link) is 15m (approximately 50ft). (Sample calculations will be shown in the final path profile and in the Design Computations).

III. TOWERS Radio

masts

and

towers

are,

support antennas (also known as aerials)

typically,

tall

structures

designed

to

for telecommunications and broadcasting,

including television. The terms "mast" and "tower" are often used interchangeably. However,

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in

structural

engineering

terms,

a

tower

is

a

self-supporting

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MICROWAVE LINK COMMUNICATION DESIGN or cantilevered structure, while a mast is held up by stays or guys. In selecting what type of tower to use, the following should be considered first.



Rigidity - The capability of the tower to hold loads such as antennas and cables prior to construction.



Height - The height of the tower must be enough in order to avoid obstructions.



Wind Loading - The anticipated wind loading has to be identified under harsh and additional loading.



Land Area – The land area will determine the kind of towers that can be employed.



Cost – The cost of the antenna will vary depending on height and wind loading.

These are the parameters that will be considered when choosing what type of tower to use – monopole, self-supporting or guyed towers.

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MICROWAVE LINK COMMUNICATION DESIGN MONOPOLE TOWERS Monopole towers are of a single pole design and are generally used in cellular and personal communication service. They are free standing and are usually built cylindrically or with multiple sides. Monopole towers are often placed on the roofs of tall buildings. Each section of the monopole is welded or bolted together to a height ranging from 30 to 490 feet. The section with the largest diameter is at the bottom of the tower, with each successive section smaller as the tower rises. This decrease in diameter contributes to the low wind resistance of monopole towers compared to other tower types.

SELF-SUPPORTING TOWERS Self-supporting towers have a larg...