Antenna Systems Flashcards
7 cards from real SBCA 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 Systems flashcards as text
What is the primary purpose of a feed horn in a parabolic dish antenna system?
Answer: To collect and focus the reflected signal from the dish onto the LNB
The feed horn collects the reflected electromagnetic energy from the parabolic dish surface and focuses it onto the LNB input.
Which antenna parameter describes the ratio of power radiated in the direction of maximum radiation to the average power radiated in all directions?
Answer: Directivity
Directivity is the ratio of maximum radiation intensity to the average radiation intensity, independent of antenna efficiency.
A dish antenna has an efficiency of 60% and a physical aperture area of 1.5 m². What is its effective aperture area?
Answer: 0.9 m²
Effective aperture = efficiency × physical aperture = 0.60 × 1.5 m² = 0.9 m².
What does the term 'cross-polarization discrimination' (XPD) measure in a satellite antenna system?
Answer: The ratio of desired polarization signal power to the undesired orthogonal polarization power
XPD quantifies how well an antenna discriminates between two orthogonal polarizations, which is critical for frequency reuse systems.
In a satellite uplink system, which condition causes antenna 'gain compression' at high power levels?
Answer: The high-power amplifier (HPA) driving the antenna enters nonlinear saturation
Gain compression occurs in the HPA when input power is high enough to drive the amplifier into its nonlinear region, reducing effective output gain.
What is the effect of increasing a parabolic dish's f/D ratio (focal length to diameter) on antenna performance?
Answer: Results in a shallower dish with wider feed illumination angle requirements
A higher f/D ratio produces a shallower (less deep) dish, requiring a feed horn with a wider illumination angle to cover the full reflector surface.
Which type of antenna mount allows a single actuator to track all geostationary satellites visible from a fixed location?
Answer: Polar (hour angle-declination) mount
A polar mount aligns one rotation axis with Earth's polar axis, so a single motor sweep follows the geostationary arc without requiring a second axis adjustment.