Chapter 4 Flashcards
Few Statements that will help to interpret the radiation charts?
Azimuth chart - H-plane = Top-down view
Elevation chart = E-plane = side view
What are azimuth chart and elevation chart referred to?
Polar charts
What is a beamwidth?
Beamwidth is the measurement of how broad or narrow the focus of an antenna is, and is measured both horizontally and vertically.
What are some Antenna Types?
Omnidirectional
Semidirectional
Highly Directional
What is Omnidirectonal antenna?
Omnidirectional Antenna radiates RF in fashion similar to the way a table or floor lamp radiates light. All directions
What is Semidirectional Antenna?
They radiate RF in a fashion similar to the way a wall sconce radiates light away from the wall or the way a street lamp shines down a street or a parking lot.
Providing a directional light across a large area
What is a highly directional antenna?
Radiate RF in a fashion similar to the way spotlight focuses light on a flag or a sign.
When are Omnidirectional Antennas used?
They are used in point-to-multipoint environments.
Where are Semidirectional Antennas commonly used?
To provide a network bridge between two building in a campus environment or down the street from each other.
Three types of semidirectional antennas?
Patch
Panel
Yagi
What is patch antenna?
Particular way of designing the radiating elements inside the antenna.
Used for outdoor point-to-point communications.
When are highly directional antennas used?
Strictly used for point-to-point communications. To provide network bridging between two buildings. Most narrow beamwidth.
Two types of highly directional antennas?
Parabolic Dish Antenna
Grid Antenna
What is an Antenna Array?
Is a group of two or more antennas that are integrated together to provide coverage. These antennas operate together to perform what is known as beamforming.
What is a beamforming?
Beamforming is a method of concentrating RF energy. Concentrating a signal means that the power of the signal will be greater and the SNR at the receiver should therefore also be greater, providing better transmission.
Three different types of beamforming?
Static Beamforming
Transmit Beamforming
Dynamic Beamforming
What is a Static Beamforming?
Performed by using directional antennas to provide a fixed radiation pattern.
Uses multiple directional antennas, all clustered together.
What is a Dynamic Beamforming?
Focuses the RF energy in a specific direction and in a particular shape. The radiation pattern of the signal can change on a frame by frame basis.
What is Transmit Beamforming?
Is performed by transmitting multiple phase-shifting signals with the hope and intention that they will arrive in phase at the location where transmitter believes that the receiver is located. Pattern is not dynamic
What is a Fresnel Zone?
Path of the visual LOS between two point-to-point antennas.
What is a MIMO?
Multiple Input Multiple Output
Take advantage of multipath. Wireless radio architecture that can receive or transmit using multiple antennas concurrently.
What is the definition of the horizontal beamwidth of an antenna?
The distance between the two -3dB power points on the horizontal axis, measured in degrees.
The fresnel zone should not be blocked by more than what percentage to maintain a reliable communications link?
40 Percent
The size of Fresnel zone is controlled by what factors?
Distance
Frequency
When a long-distance point-to-point link is installed, earth bulge should be considered beyond what distance?
7 Miles
Which of the following are true for antenna diversity?
The transreceiver samples both antennas and chooses the best received signal from one antenna.
Transreceivers can transmit from only one of the antennas at a time
The ratio between the maximum peak voltage and minimum voltage on a line is known as what?
VSWR
What are some of the possible negative effects of an impendence mismatch?
Erratic Signal Strength
Decreased signal amplitude
Amplifier/transmitter failure
When determining the mounting height of a long-distance point-to-point antenna, which of the following needs tobe considered?
Frequency
Distance
Earth Bulge
RF line of sight
Which of the following are true about cables?
They cause impedance on the signal
They add loss to the signal
Lightning arrestors will defend against what?
Transient currents
The radius of the second Frensel zone is?
Out of phase with the point source
Larger than the first frensel zone
