CAD CAD Antenna Designer Practical Applications and Systems 2 — Questions and Answers
Question 1: When installing a Yagi-Uda antenna for point-to-point communication, what alignment step most directly maximizes received signal strength?
- Boresighting both antennas so their maximum gain axes are co-aligned (Correct answer)
- Matching the antenna feed impedance to 600 Ω
- Orienting the antenna with the reflector facing the transmitter
- Tilting the antenna 15° below horizontal
Correct answer: Boresighting both antennas so their maximum gain axes are co-aligned
Boresighting ensures both Yagi antennas' main lobes point directly at each other, maximizing the effective gain on the link and thereby received signal strength.
Question 2: What is the main advantage of using a log-periodic dipole array (LPDA) antenna in a broadband signal monitoring application?
- Consistent gain and impedance across a wide frequency range (Correct answer)
- Extremely high gain at a single design frequency
- Omni-directional pattern in both azimuth and elevation
- Very small physical size at all operating frequencies
Correct answer: Consistent gain and impedance across a wide frequency range
LPDAs maintain relatively constant gain and input impedance across a wide frequency range, making them ideal for broadband spectrum monitoring and signal interception.
Question 3: In a vehicle-mounted antenna installation, what grounding practice is essential for proper antenna performance and safety?
- Ensuring a low-impedance RF ground bond between the antenna mount and vehicle chassis (Correct answer)
- Using only RG-8 coaxial cable regardless of frequency
- Mounting the antenna at least 2 meters above the roofline
- Installing a ferrite choke on the DC power line only
Correct answer: Ensuring a low-impedance RF ground bond between the antenna mount and vehicle chassis
A solid low-impedance RF ground bond between the antenna mount and vehicle chassis ensures the antenna operates against the correct ground plane and prevents RF voltage on chassis components.
Question 4: What distinguishes an active antenna from a passive antenna in a receiving system?
- An active antenna includes an integrated low-noise amplifier (LNA) near the element (Correct answer)
- An active antenna uses a larger aperture for higher gain
- An active antenna requires no impedance matching
- An active antenna is made from electronically conductive polymer materials
Correct answer: An active antenna includes an integrated low-noise amplifier (LNA) near the element
An active antenna integrates an LNA at or near the antenna element to amplify weak signals before cable losses degrade the system noise figure.
Question 5: A choke balun placed at the feed point of a dipole antenna primarily serves what function?
- Preventing RF current from flowing on the outer shield of the coaxial feed line (Correct answer)
- Increasing the antenna's radiation resistance
- Providing a DC path to ground for lightning protection
- Lowering the antenna's resonant frequency by adding inductance
Correct answer: Preventing RF current from flowing on the outer shield of the coaxial feed line
A choke balun blocks common-mode (shield) currents on the coaxial feed line that would otherwise distort the dipole's symmetric radiation pattern.
Question 6: What is the primary purpose of a tower-mounted amplifier (TMA) in a cellular base station antenna system?
- Improving uplink sensitivity by amplifying received signals close to the antenna before tower cable losses (Correct answer)
- Increasing downlink transmit power beyond the base station amplifier limits
- Converting the antenna's circular polarization to linear polarization
- Filtering adjacent channel interference from the downlink signal
Correct answer: Improving uplink sensitivity by amplifying received signals close to the antenna before tower cable losses
A TMA (also called a mast-head amplifier) amplifies uplink received signals at the tower top before they travel down lossy feeder cables, improving overall system noise figure and uplink coverage.
CAD CAD Antenna Designer Practical Applications and Systems 2
When installing a Yagi-Uda antenna for point-to-point communication, what alignment step most directly maximizes received signal strength?