CAD CAD Antenna Designer Practical Applications and Systems 1 — Questions and Answers
Question 1: In a cellular base station, what is the primary purpose of using a sector antenna instead of an omnidirectional antenna?
- To concentrate radiated power into specific angular regions for increased capacity (Correct answer)
- To reduce tower height requirements
- To eliminate the need for a transmission line
- To comply with FCC Part 15 power limits
Correct answer: To concentrate radiated power into specific angular regions for increased capacity
Sector antennas divide the coverage area into angular sectors, concentrating gain and allowing frequency reuse across sectors to increase network capacity.
Question 2: What type of antenna is most commonly used in GPS receivers due to its ability to receive circularly polarized signals from any satellite elevation angle?
- Patch (microstrip) antenna (Correct answer)
- Dipole antenna
- Log-periodic antenna
- Helical antenna
Correct answer: Patch (microstrip) antenna
Patch antennas are widely used in GPS receivers because they are compact, low-profile, and provide the right-hand circular polarization needed for GPS L1/L2 signals.
Question 3: Which antenna characteristic is most critical when designing a direction-finding (DF) system for locating an unknown transmitter?
- Sharp azimuthal pattern with well-defined null direction (Correct answer)
- Maximum gain in all directions
- Broadband impedance match below −10 dB
- Vertical polarization only
Correct answer: Sharp azimuthal pattern with well-defined null direction
Direction-finding systems rely on antennas with sharp pattern nulls to precisely determine the bearing toward an unknown transmitter.
Question 4: A MIMO wireless system uses multiple antennas primarily to achieve what benefit?
- Increased data throughput via spatial multiplexing or diversity gain (Correct answer)
- Reduced antenna size
- Elimination of impedance matching requirements
- Higher operating frequency
Correct answer: Increased data throughput via spatial multiplexing or diversity gain
MIMO (Multiple Input Multiple Output) systems exploit multiple antennas at transmitter and receiver to achieve spatial multiplexing or diversity, boosting data throughput and link reliability.
Question 5: What is the role of a radome in an antenna system installation?
- To protect the antenna from environmental conditions while minimizing RF performance degradation (Correct answer)
- To increase antenna gain through reflective surfaces
- To filter out-of-band signals before they reach the feed
- To ground the antenna structure for lightning protection
Correct answer: To protect the antenna from environmental conditions while minimizing RF performance degradation
A radome is a weatherproof enclosure that protects an antenna from wind, rain, ice, and UV radiation while being electrically transparent to minimize signal loss.
Question 6: In phased array radar, what physical mechanism allows the beam to be steered electronically without mechanically moving the antenna?
- Progressive phase shifts applied to each array element (Correct answer)
- Variable element spacing using servomotors
- Frequency changes that shift the beam via grating lobes
- Amplitude tapering across the aperture
Correct answer: Progressive phase shifts applied to each array element
Electronic beam steering in phased arrays is achieved by applying progressive phase shifts across individual elements, causing constructive interference in the desired scan direction.
CAD CAD Antenna Designer Practical Applications and Systems 1
In a cellular base station, what is the primary purpose of using a sector antenna instead of an omnidirectional antenna?