CompTIA Security Plus Mock Test Q179

An administrator wants to establish a WiFi network using a high gain directional antenna with a narrow radiation pattern to connect two buildings separated by a very long distance. Which of the following antennas would be BEST for this situation?

A. Dipole
B. Yagi
C. Sector
D. Omni

Correct Answer: B
Section: Network Security

Explanation:
A Yagi-Uda antenna, commonly known simply as a Yagi antenna, is a directional antenna consisting of multiple parallel dipole elements in a line, usually made of metal rods. It consists of a single driven element connected to the transmitter or receiver with a transmission line, and additional parasitic elements: a so-called reflector and one or more directors. The reflector element is slightly longer than the driven dipole, whereas the directors are a little shorter. This design achieves a very substantial increase in the antenna’s directionality and gain compared to a simple dipole.

Incorrect Answers:
A: The 15 cm long vertical element you see on most Wi-Fi equipment is actually a dipole antenna. It consists of two elements and is popular because of its omnidirectional radiation pattern.
C: A sector antenna is a type of directional microwave antenna with a sector-shaped radiation pattern. The word “sector” is used in the geometric sense; some portion of the circumference of a circle measured in degrees of arc. 60°, 90° and 120° designs are typical, often with a few degrees ‘extra’ to ensure overlap and mounted in multiples when wider or full-circle coverage is required.
D: An omnidirectional antenna is designed to provide a 360-degree pattern and an even signal in all directions

References:
http://en.wikipedia.org/wiki/Yagi-Uda_antenna
http://www.techrepublic.com/blog/data-center/80211-time-to-clear-up-some-antenna-misconceptions/
http://en.wikipedia.org/wiki/Sector_antenna#See_also
Dulaney, Emmett and Chuck Eastton, CompTIA Security+ Study Guide, 6th Edition, Sybex, Indianapolis, 2014, p. 178