Sunday, April 1, 2012

Tutorial: Microwave Link Planning - Part 1: Basics

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This is a photo of Codan 8800 series Digital m...Microwave links generally operate between frequencies of 2 and 58 GHz. Initially analogue links were used, but now far superior digital microwave links are used. Digital microwave links have many advantages over the analogue microwave links, some of which are:
·         high tolerance against interference;
·         high tolerance against deep fading;
·         high signal carrying capacity ranging from 2 to 155 Mbps;
·         high frequency range (2–58 GHz);
·         easy, rapid (and hence economical) installations.
As the frequency increases, the length of the link decreases. Due to the high frequency range (2–58GHz), the microwave links can be classified into three main categories:

(a) Long haul
(c) Short haul

Long Haul
The frequency of operation of these links is usually 2–10 GHz. In the best of climatic conditions and
frequency of operation, the distance covered by the links could range from 80 km to 45 km. These links
are affected by multipath fading (explained later).

Frequency band 2 GHz

·         Maximum path length 80 km
·         Multipath fading
·         Antenna diameters up to 370 cm for an antenna gain of 36 dB
·         Both vertical and horizontal polarisations used

Frequency band 7 GHz

·         Maximum path length about 50 km
·         Multipath fading
·         Antenna diameters up to 370 cm for an antenna gain of 46.8 dB
·         Both vertical and horizontal polarisations used

Frequency band 10 GHz

·         Maximum path length about 45 km
·         Multipath fading
·         Antenna diameters 60–120 cm for a gain range of 34–40 dB
·         Both vertical and horizontal polarisations used


Medium and Short Haul
The frequency of operation of these links is usually from 11 GHz to 23 GHz. Depending upon the climatic
conditions and frequency of operation, the hop length can vary between 40 km and 20 km. These links
are also affected by multipath fading and rain fading.

Frequency band 13 GHz

·         Maximum path length about 40 km
·         Multipath fading
·         Antenna diameters 60–120 cm for a gain range of 36.4–42.4 dB
·         Both vertical and horizontal polarisations used
Frequency band 15 GHz

·         Maximum path length about 35 km
·         Multipath fading
·         Antenna diameters 60–120 cm for a gain range of 38–44 dB
·         Both vertical and horizontal polarisations used

Frequency band 18 GHz

·         Maximum path length 20 km
·         Rain and multipath fading
·         Antenna diameters 60–180 cm for a gain range of 39–49 dB
·         Both vertical and horizontal polarisations used
·         Atmospheric attenuation 0.1 dB/km.
·         Attenuation due to rain about 1 dB/km at a rain rate of 20 mm/h

Frequency band 23 GHz

·         Maximum path length about 18 km
·         Rain and multipath fading
·         Antenna diameters 30–120 cm gain for a gain range of 35.5–47.3 dB
·         Both vertical and horizontal polarisations used
·         Atmospheric attenuation 0.1 dB/km
·         Attenuation due to rain about 3 dB/km at a rain rate of 20 mm/h

Before an into explanation is given of various factors that affect the performance of the microwave
links, an attempt will be made to explain the fundamentals of functioning of microwave links.

Next : What is Microwave Link
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