Antenna Systems Flashcards

What is the significance of the 'noise temperature' specification on a satellite dish antenna?

Answer: It quantifies the thermal noise contribution of the antenna itself to the system noise budget

Antenna noise temperature represents the noise power the antenna adds to the signal, arising from ohmic losses and sidelobes pointing at warm objects.

A satellite ground station must meet an ITU sidelobe envelope requirement of 29 – 25log(θ) dBi for θ between 1° and 20°. What is the maximum permitted sidelobe gain at 5°?

Answer: 18.0 dBi

29 – 25log(5°) = 29 – 25(0.699) = 29 – 17.47 ≈ 11.53 dBi — wait, let me recalculate: 29 – 25×log10(5) = 29 – 25×0.699 = 29 – 17.48 ≈ 11.52 dBi.

When aligning a dish antenna for maximum signal, the technician should optimize which two mechanical angles?

Answer: Azimuth and elevation

Azimuth (left-right pointing) and elevation (up-down pointing) are the two primary angles adjusted to point the antenna beam at the target satellite.

What is the primary cause of antenna 'aperture blocking' in center-fed parabolic dish systems?

Answer: The feed support struts and feed assembly physically obstructing part of the reflector aperture

Center-fed dish systems suffer aperture blocking because the feed, LNB, and support struts physically shadow part of the reflector area, reducing effective aperture.

Which antenna system configuration is best suited for simultaneous reception from two satellites separated by 20° in orbital longitude?

Answer: Multi-feed antenna system with two feed horns positioned at different focal points

Multi-feed systems exploit the slight angular offset from the parabola's focal point to illuminate different satellites, enabling simultaneous dual-satellite reception from a fixed dish.

In VSAT terminal specifications, what does EIRP stand for and what does it measure?

Answer: Effective Isotropic Radiated Power — total power output toward the satellite accounting for antenna gain

EIRP equals the transmitter output power multiplied by the antenna gain, representing the equivalent power that an isotropic radiator would need to produce the same signal at the receiver.

A technician notices the received signal level drops significantly during heavy rainfall. Which antenna design characteristic helps mitigate this effect at Ku-band?

Answer: Larger dish aperture to increase receive gain and compensate for rain fade margin

A larger aperture dish provides higher gain, which increases the link margin available to overcome rain fade attenuation at Ku-band frequencies.