CNIT 346 Chapter 4

Radiation patterns

Commonly known as polar charts. Created in controlled environments; outer ring represents strongest signal. Scaled in dB from outer ring inward.

Azimuth Chart

Horizontal plane (top down) view of signal propagating from a central point.

Elevation Chart

Elevation plane view of signal propagating from a central point. (side view/vertical)

Beamwidth

Measurement of how broad or narrow the focus of an antenna is both horizontally and vertically. Taken from the strongest point on the polar chart to the half power points (-3 dB). Measured in degrees between the points.

Omnidirectional Antenna

Radiates in all directions to provide general coverage. Typically a dipole antenna with bagel-shaped coverage and used for point-to-multipoint networks.

Semidirectional Antenna

Has a wide directionalized focus. Used for short to medium distance communications, three types: patch, panel, and yagi. Has a horizontal beamwidth less than 180 degrees.

Highly Directional Antena

Has a narrow directional focus. Most focused, narrow beamwidth. Strictly used for point-to-point communications. Two types: grid and parabolic dish.

Sector Antennas

High gain, semi-directional antennas which generate very little RF signal behind the antenna. Has pie-shaped coverage between 60 and 180 degrees.

Sectorized array

multiple sector antennas installed as a group to provide 360 degrees of horizontal coverage. Have a narrow vertical bandwidth of 7-17 degrees.

Antenna Arrays

Group of two or more antennas integrated to provide coverage.

Beamforming

Concentrating RF energy by combining signals from a set of small omni-directional antennas. Simulates a large directional antenna.

Static Beamforming

Using directional antennas to provide a fixed radiation pattern. Also known as a sectorized array.

Dynamic Beamforming

Focuses the RF energy in a specific direction and particular shape in the direction of an individual client. Broadcasts frames omnidirectionally, but chage on a frame-by-frame basis. Known as beamstearing and smart antenna technology.

Transmit Beamforming (TxBF)

Multiple phase-shifted signals are transmitted to arrive in-phase at the location of a receiver. Considered a digital signal processing technology. Technically not an antenna technology.

Visual Line of Sight (LOS)

Perceived straight line that light travels along. Has no bearing on successful RF transmission. Usually not true due to refraction, diffraction, and reflection.

RF Line of Sight

Requires an unobstructed LOS between two antennas. Additional area called a Fresnel zone around the visual LOS is needed.

Fresnel Zone

The additional area surrounding the visual LOS between two point-to-point antennas. > 40% obstruction will make the link unreliable. Theoretically an infinite number exist. Only the first two matter in practice; frequency and distance effect size.

Earth Bulge

Curvature of the earth that must be considered if a link is greater than 7 miles.

Antenna Polarization

Orientation of the amplitude of the RF waves (vertical and horizontal). Transmitting and receiving antennas must have the SAME.

Antenna Diversity

Exists when a wireless device has two antennas and receivers functioning together.

Receive Diversity

Describes radios using switched diversity where they listen with multiple antennas but only process the signal with the best amplitude.

Transmit diversity.

Describes radios using the antenna that was last used to receive.

Multiple-Input Multiple-Output (MIMO)

More sophisticated form of antenna diversity. Radio Architecture which can receive or transmit using multiple antennas concurrently. Used by 802.11n and 802.11ac. improves reliability, range, and throughput.

Indoor MIMO

3 omni antennas

Outdoor MIMO

2 omni antennas

Voltage Standing Wave Ratio (VSWR)

Backfeed from the antenna into the signal line. This causes signal loss and is due to poor antenna mounting techniques and interference from the environment.