Antenna Theory and Design Flashcards
7 cards from real HAM practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Antenna Theory and Design flashcards as text
What is the radiation pattern of a two-element phased vertical array with elements spaced one-quarter wavelength apart and fed 90 degrees out of phase?
Answer: Cardioid (heart-shaped) pattern
Two vertical elements spaced λ/4 apart and fed 90° out of phase produce a cardioid pattern with maximum radiation in one direction and a null in the opposite direction.
What is the self-resonant frequency of an antenna primarily determined by?
Answer: The physical length of the antenna relative to the wavelength
An antenna's self-resonant frequency is primarily determined by its physical length, which must be an electrical multiple of the operating wavelength.
What is the main advantage of a log-periodic dipole array (LPDA) over a single Yagi antenna?
Answer: Broader frequency coverage with relatively consistent performance
An LPDA covers a wide frequency range (often several octaves) with consistent gain and impedance, unlike a Yagi which is optimized for a single frequency.
What is aperture efficiency in the context of a dish antenna?
Answer: The ratio of the effective aperture to the physical aperture area
Aperture efficiency is the ratio of the antenna's effective aperture to its physical aperture area, typically ranging from 50% to 75% for practical dish antennas.
What type of antenna is formed when two quarter-wave vertical antennas are fed 180 degrees out of phase?
Answer: Phased array with a bidirectional broadside pattern
Two verticals fed 180° out of phase and separated appropriately create a bidirectional broadside pattern perpendicular to the line joining the elements.
What is the antenna gain of a half-wave dipole relative to an isotropic radiator (dBi)?
Answer: 2.15 dBi
A half-wave dipole has 2.15 dBi gain over an isotropic radiator due to its figure-8 radiation pattern concentrating energy in two directions.
What is the effect of increasing the diameter of a dipole antenna element?
Answer: Broadens the antenna bandwidth and lowers the Q
Using a larger diameter conductor lowers the antenna's Q factor and broadens its bandwidth, allowing operation over a wider frequency range.