Microwave Part 1

Microwaves

electromagnetic waves with frequencies ranging from 300 MHz to 300 GHz

Microwaves

Due to the inherent high frequency of these EM waves, their wavelengths are relatively shorter compared to the wavelengths of conventional RF signals

Microwaves

Propagate in space in a straight line like beams of light

Microwaves

Can be reflected by conductive surfaces

Microwaves

The current created by Microwaves travel through a thin out layer of conductor

Microwaves

They penetrate through the ionosphere

Advantages of Microwaves

• More data can be sent due to its high frequency

• Requires smaller antennas

• Signals can easily propagate around physical obstacles

• Improved directive properties reduce the risk of interference and minimal crosstalk

• Much less background noise

• Fewer repeaters are necessary for amplification

• Does not require physical facilities like underground cables

• Does not require right-of-way

• Less fading

• Does not require high transmit power

• Minimum delay times

• Lower start-up and operational costs

Disadvantages of Microwaves

• More difficult to analyze and design circuits at microwave frequencies

• Difficult to implement measuring techniques

• Conventional components behave differently at microwave frequencies

• Conventional semiconductors do not work properly at microwave frequencies

• Transit time is more critical

• Requires use of specialized components

• Transmission distance is limited by line-of-sight

• Microwaves are easily diverted due to their short wavelengths

• Prone to absorption and attenuation by fog and heavy rains

• Cost of building the infrastructure is high

Safety of Microwaves

• Microwaves are non-ionizing

• Has insufficient energy to cause cancer or change in DNA composition

• Links have limited power, typically a few hundred watts

ITU

set up by the UN, is responsible for controlling the allocation of spectrum

ITU-T

handles standards for end-to-end circuits covering all media

ITU-R

deals with radio link

Microwave Communication System

A form of electronic communications the uses microwaves to transmit and receive information signals

microwave link

Simplest form of Microwave Communication System

microwave link

a high frequency radio link designed to provide a signal connection between two points

hop

Two microwave terminals form a_____

Microwave Radio

a point-to-point fixed digital link that operates in duplex mode

Duplex Mode

means that each channel consists of a pair of frequencies for transmission and reception

Duplex Mode

Sometimes called low-band channels and high-band channels

T to R spacing

Spacing between two frequencies

Frequency Division Duplexer

The transmit and receive frequencies are combine in a single antenna using a _____

Microwave Radio

The transmit and receive frequencies are combine in a single antenna using a Frequency Division Duplexer

duplexer

provides coupling for the two signals

Digital modem
RF unit
Passive Parabolic Antenna

A microwave radio terminal has 3 basic module:

Digital modem

to interface with the customer Microwave Radio: Modules and Hardware Configurations equipment and convert customer traffic to a modulated signal

RF unit

to up and down convert signal in RF range

Passive Parabolic Antenna

transmission and reception of signals

E1

basic digital channel containing 30 voice channels Microwave Radio: Capacity Configurations and 2 other channels (for sync and signaling) at 64 kbps each and time division multiplexed

30 voice channels, 64 kbps

E1is the basic digital channel containing ____and 2 other channels (for sync and signaling) at____ each and time division multiplexed

E1

has a total bit rate of 2.038 Mbps

2.038 Mbps

E1has a total bit rate of _______

non-protected

1 + 0 configuration

protected

1 + 1 configuration

Monitored Hot Standby (MHSB)

1 + 1 configuration or protected

• Analog
• Digital

Based on nature of signal

Short Haul

uses frequencies greater than 15 GHz

Long haul

uses lower frequencies to minimize attenuation

Narrowband

generally less than 3 GHz in frequency

Wideband

utilizes frequencies from 3 GHz to 15 GHz

Microwave links

are used for the control and maintenance of the power grid

Microwave links

are used to connect radio/TV repeaters to main and regional transmission sites

Microwave links

are used for BTS-BTS, BTS-BSC, BSC-MSC MSC-PSTN connections

16 kbps

Bit rate for one voice GSM channel

120 VC

1 GSM E1 is

Snell’s Law

refraction

the radio horizon is extended due to

radio horizon

approximately one-third greater than the visual horizon for standard atmospheric conditions

𝑵= 𝒏−𝟏 𝒙𝟏𝟎^6

Radio Refractivity

refractive index

non-ionized atmosphere is always greater than 1

Refractivity gradients

change with time leading to anomalous propagation conditions

Microwave beams

travel in the atmosphere along curved paths

effective Earth radius

In designing MW links, a microwave beam is assumed to be traveling along a straight line relative to an ______ , adjusted by the refractivity gradient

k-factor

The effective Earth radius is the actual radius multiplied by the _____

k-factor

ratio of the effective radius to the actual radius of the earth

k-factor

It is used to determine the relative clearance and not to predict the beam curvature

k-factor

a numerical figure that considers the non ideal condition of the atmospheric refraction that causes the beam to be bent toward to, or away from the eart

standard refraction

when the gradient of refractivity displays average characteristics

k= 4/3

During a standard atmospheric condition, k=

Cold or dry climates and high altitudes

have lower k-factor

Coastal areas

where humidity is high will have higher k facto

Superstandard Refraction

Also called super refraction

Superstandard Refraction

results from meteorological conditions such as temperature inversion or marked decrease in total moisture content of the air

Superstandard Refraction

result from excessing increase in water vapor content near the surface

Superstandard Refraction

In this condition, the value of k approaches infinity and the microwave beam follows the contour of the earth and becomes partially parallel to it

Substandard Refraction

This occurs when the dielectric constant of the atmosphere increases with height

inverse beam bending or earth bulging

The microwave beam tends to be deflected away from the earth and is usually

less than 1

K-factor for substandard refraction is

temperature inversion and negative humidity gradient or hydrolapse

Negative refractivity gradient results from

Temperature inversion

is the primary cause of ducts which influence radio link propagation

blackout

G becomes negative

Ground-based Duct

a very dense layer of air close to the ground with a thin layer on top of it

Elevated duct

exists when the atmosphere has a thick layer in some height above the ground

Ducting Probability

Refers to the percentage of time when dN/dh is less than 100N/km for a specified month

ITU-R

issues DUCT Probability Contour Maps

Equatorial regions

most vulnerable to ducts

G is -157

the microwave beam would be parallel to the earth