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CHAPTER 4 : HOW ANTENNAS WORK (ANTENNA SYSTEM IMPLEMENTATION (OTHER…
CHAPTER 4 : HOW ANTENNAS WORK
GAIN N LOSS
DECIBEL
ratio between two signal levels
For microwave and higher frequency antennas, the gain is usually expressed in dB dipole (dBd).
isotropic radiator, a theoretically perfect sphere that radiates energy equally in all directions.
not possible; it would need a power or signal cable connected to it at some point on the surface of the sphere
reference point; expressed using dB isotropic
ANTENNAS CHARACTERISTICS
ANTENNAS TYPES
Passive antennas
does not amplify the signal
Active antennas
passive antennas with built-in amplifiers.
RF signal and the power for the amplifier are supplied on the same conductor to reduce the cost and make active antennas easier to install
SIZES N SHAPES
3 characteristics
frequency that the antenna is designed
direction of the wave
power with which the antenna must transmit or how sensitive it needs to be to receive very weak signals
Omnidirectional
transmit and receive signals from all directions
Directional
transmit a signal in one direction only
Yagi
wider, less-focused RF energy beam
used for outdoor applications
parabolic dish antenna
narrow, more concentrated beam of RF energy
receive satellite signals
Patch antennas
emit an RF energy beam that is horizontally wide but vertically taller than that of a yagi antenna
Considered a semi-directional antenna
send signal energy down a long corridor
SIGNAL STRENGTH AND DIRECTION
HOW ANTENNAS WORK
WAVELENGTH
length of a single RF sine wave
determines the size of an antenna
full-wave antenna; full length of the wave where a signal transmit/receive most efficiently at a specific frequency
ANTENNA PERFORMANCES
RADIATION PATTERN
a graphic measuring the signal radiating from the antenna
usually drawn as if you were looking at it from the top
ANTENNA POLARIZATION
orientation of the wave leaving the antenna
ANTENNA DIMENSIONS
One-dimensional
dipole
monople
two-dimensional
patch and satellite dish
another type; horn antenna
common in telephone networks
transmit high-power microwave signals between two distant towers
SMART ANTENNAS
primarily in cellular telephony and WiMAX
“learn” where it is located/coming, track it, and focus to the direction to avoid wasting energy and to prevent interference with other antennas
send narrow beams of energy toward the receiver
2 clasees
switched beam antenna
uses several narrow beam antennas pointing in different directions and turns each one on or off as the receiver moves
adaptive or phased array antenna
divided into a matrix of radiating elements
signal processor is used to detect which elements receive a stronger signal
turn matrix on off
used extensively in ultramodern radar systems
how efficiently an antenna can radiate an RF signal
ANTENNA SYSTEM IMPLEMENTATION
ANTENNA CABLES
Most antennas use coaxial cable
cable that is too thick for keeping loss at minimum
RF PROPAGATION
way that radio waves propagate, or move, between the transmitter and the receiver
3 groups
Sky waves
Line-of-sight
Ground
POINT2MULTIPOINTS LINKS
uses omnidirectional antenna
POIN2POINT LINKS
directional antennas
FRESNEL ZONE
elliptical region ; space between the two antennas
at least 60 percent of the Fresnel zone must be kept clear of obstructions
LINK BUDGETS
calculate whether you will have enough signal strength to meet the receiver’s minimum requirements
ANTENNAS ALLIGNMENTS
position the antennas at the same height and point them toward one another to maximize the strength of the signal
tools to assist
compass
spotting scope or binoculars
means of communication; phone
light source
spectrum analyzer; displays the signal amplitude and frequency and can also detect interference in a particular frequency channel
OTHER CHALLENGES OF OUTDOOR LINKS
absorbed by various materials
Weather phenomena
check history region's
Contact authority to identify short- and long-term plans
vegetation growth
possibility of another company or person setting up another RF wave beam