Chapter 4 - Radio Frequency Signal and Antenna Concepts Flashcards
The installation of _____ has the greatest ability to affect whether or not the communication is successful.
antennas
To assist potential buyers with their purchasing decision, antenna manufacturers create _____ _____ and elevation charts, commonly known as _____ _____, for their antennas. These radiation patterns are created in controlled environments where the results cannot be skewed by outside influences and represent the signal pattern that is radiated by a particular model of antenna. These charts are commonly known as _____ or _____ _____ _____.
azimuth charts, radiation patterns, polar charts, antenna radiation envelopes
With an antenna, the radiation pattern will grow larger or smaller depending on how much power the antenna receives, but the shape and the relationships represented by the patterns will always _____ _____ _____.
stay the same
Remember that the logarithmic scale is a _____ scale, based on exponential values, so the polar chart is actually a visual representation using a _____ scale.
variable
_____ is the measurement of how broad or narrow the focus of an antenna is— and is measured both horizontally and vertically. It is the measurement from the center, or strongest point, of the antenna signal to each of the points along the horizontal and vertical axes where the signal decreases by half power (–3 dB).
Beamwidth
The –3 dB points are often referred to as _____-_____ _____. The distance between the two _____-_____ _____ on the horizontal axis is measured in degrees, giving the horizontal beamwidth measurement. The distance between the two _____-_____ _____ on the vertical axis is also measured in degrees, giving the vertical beamwidth measurement.
half-power points
It is important when aligning point-to-point antennas that you make sure they are actually aligned to the _____ lobe and not a _____ lobe.
main, side
There are _____ main categories of antennas.
3
_____ antennas radiate RF in a fashion similar to the way a table or floor lamp radiates light. They are designed to provide general coverage in all directions.
Omnidirectional
_____ antennas 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 light down on a street or a parking lot, providing a directional light across a large area.
Semidirectional
_____ _____ antennas radiate RF in a fashion similar to the way a spotlight focuses light on a flag or a sign.
Highly directional
In addition to antennas acting as radiators and focusing signals that are being transmitted, they focus signals that are _____.
received
Omnidirectional antennas radiate RF signal in all directions. The small, rubber _____ antenna, often referred to as a rubber duck antenna, is the classic example of an omnidirectional antenna and is the default antenna of most access points.
dipole
The closest thing to an _____ _____ is the omnidirectional dipole antenna.
isotropic radiator
As it relates to omnidirectional dipole antennas, it is important to know that the higher the dBi or dBd value of an antenna, the more _____ the signal.
focused
The horizontal beamwidth of omnidirectional antennas is always _____ degrees, and the vertical beamwidth ranges from 7 to 80 degrees, depending on the particular antenna.
360
Indoor installations typically use low-gain omnidirectional antennas with gain of about _____ dBi.
2.14
Antennas are most effective when the length of the element is an _____ _____ (such as 1/4 or 1/2) or a multiple of the wavelength (l).
even fraction
Higher-gain omnidirectional antennas are typically constructed by stacking multiple dipole antennas on top of each other and are known as _____ _____.
collinear antennas
Omnidirectional antennas are typically used in _____-_____-_____ environments. The omnidirectional antenna is connected to a device (such as an access point) that is placed at the center of a group of client devices, providing central communications capabilities to the surrounding clients.
point-to-multipoint
It is common to use _____ antennas to provide a network bridge between two buildings in a campus environment or down the street from each other. Longer distances would be served by highly directional antennas.
semidirectional
What are the 3 types of semidirectional antennas?
Patch, Panel, Yagi
Patch and panel antennas, as shown in Figure 4.10, are more accurately classified or referred to as _____ antennas.
planar
Planar antennas can be used for outdoor _____-_____-_____ communications up to about a mile but are more commonly used as a central device to provide unidirectional coverage from the access point to the clients in an indoor environment. It is common for patch or panel antennas to be connected to access points to provide directional coverage within a building.
point-to-point
Since planar antennas have a horizontal beamwidth of _____ degrees or less, a minimal amount of signal will radiate outside of the building.
180
_____-_____ antennas are typically used for short- to medium-distance point-to-point communications of up to about 2 miles.
Yagi-Uda
_____ _____ antennas are strictly used for point-to-point communications, typically to provide network bridging between two buildings. They provide the most focused, narrow beamwidth of any of the antenna types.
Highly directional
There are two types of highly directional antennas: _____ _____ antennas and _____ antennas.
parabolic dish, grid
The _____ _____ antenna is similar in appearance to the small digital satellite TV antennas that can be seen on the roofs of many houses.
parabolic dish
The _____ antenna resembles the grill of a barbecue, with the edges slightly curved inward. The spacing of the wires on a _____ antenna is determined by the wavelength of the frequencies that the antenna is designed for.
grid
Because of the high gain of highly directional antennas, they are ideal for long-distance point-to-point communications as far as _____ miles (58 km).
35
Because of the long distances and narrow beamwidth, highly directional antennas are affected more by _____ _____ _____, which is antenna movement or shifting caused by wind. Even slight movement of a highly directional antenna can cause the RF beam to be aimed away from the receiving antenna, interrupting RF communications. In high-wind environments, grid antennas, because of the spacing between the wires, are less susceptible to wind load and may be a better choice.
antenna wind loading
_____ antennas are a special type of high-gain, semidirectional antenna that provides a pie-shaped coverage pattern. These antennas are typically installed in the middle of the area where RF coverage is desired and placed back to back with other sector antennas.
Sector
Combining multiple sector antennas to provide 360 degrees of horizontal coverage is known as a _____ _____.
sectorized array
The horizontal beamwidth of a sector antenna is from _____ to _____ degrees, with a narrow vertical beamwidth of 7 to 17 degrees.
60, 180
Sector antennas typically have a gain of at least _____ dBi.
10
Since each antenna covers a _____ area, each antenna can be connected to a separate transceiver and can transmit and receive independently of the other antennas. This provides the capability for all the antennas to be transmitting at the same time, providing much greater throughput.
separate
The gain of a sector antennas is much _____ than the gain of an omnidirectional antenna
greater
An _____ _____ 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 _____.
antenna array, beamforming
What are the 3 different types of beamforming?
Static, Transmit, and Dynamic
_____ beamforming is performed by using directional antennas to provide a fixed radiation pattern. _____ beamforming uses multiple directional antennas, all tightly clustered together but aimed away from a center point or location.
Static
Static beamforming is just another term occasionally used when referring to an _____ _____ _____.
indoor sectorized array
For static beamforming, each beam sector is assigned a different _____ channel.
nonoverlapping
_____ beamforming focuses the RF energy in a specific direction and in a particular shape. Like static beamforming, the direction and shape of the signal is focused, but unlike static beamforming, the radiation pattern of the signal can change on a frame-by-frame basis.
Dynamic
Dynamic beamforming uses an adaptive antenna array that maneuvers the beam in the direction of a targeted receiver. The technology is often referred to as smart antenna technology, or _____.
beamsteering
Dynamic beamforming can focus a beam in the direction of an individual client for _____ unicast transmissions between an access point and the targeted client. However, any broadcast frames such as beacons are transmitted using an omnidirectional pattern so that the access point can communicate with all nearby client stations in all directions.
downstream
_____ _____ is performed by transmitting multiple phase-shifted signals with the hope and intention that they will arrive in-phase at the location where the transmitter believes that the receiver is located.
Transmit beamforming (TxBF)
