Antennas and Transmission Lines Flashcards
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Read the first 7 Antennas and Transmission Lines flashcards as text
What is the approximate gain of a half-wave dipole antenna relative to an isotropic radiator?
Answer: 2.15 dBi
A half-wave dipole concentrates radiation broadside to the element in a figure-eight pattern, yielding approximately 2.15 dBi gain over an isotropic (point) radiator.
What is the primary advantage of a Yagi-Uda antenna for fixed point-to-point communication links?
Answer: It provides high directional gain toward a specific direction
A Yagi-Uda antenna uses a reflector, driven element, and one or more directors to focus radiated energy in a single direction, providing substantial gain.
What determines the polarization of a transmitted radio wave?
Answer: The orientation of the electric field, determined by the physical orientation of the radiating element
Antenna polarization is defined by the orientation of the transmitted electric field vector, which corresponds to the physical orientation of the antenna element.
What is the -3 dB beamwidth of a directional antenna?
Answer: The angular width between the two points on the main lobe where radiated power falls to half its peak value
The -3 dB beamwidth is measured between the two half-power points on either side of the main radiation lobe peak, indicating how tightly the antenna focuses its energy.
What is the radiation resistance of a half-wave dipole antenna in free space?
Answer: 73 ohms
A half-wave dipole in free space has a radiation resistance of approximately 73 ohms, which represents the resistive component of its feedpoint impedance accounting for radiated power.
What is the front-to-back ratio of a directional antenna?
Answer: The ratio of gain in the forward direction to the gain directly behind the antenna, expressed in dB
Front-to-back ratio compares the antenna's maximum forward gain to its gain exactly 180 degrees opposite, indicating how well the antenna rejects signals from the rear.
Which antenna type is most commonly used for satellite earth station communications at microwave frequencies due to its very high gain?
Answer: Parabolic reflector dish
Parabolic dish antennas focus microwave energy to or from a point feed at the focal point, achieving very high gain necessary for the long path lengths of satellite communication.