What type of antenna pattern is radiated...

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Question 1 of 20bf2JHsr1BuIpkkmNAr9u

What type of antenna pattern is radiated from a ground station phased-array directional antenna when transmitting the PPM pulses in a Mode S interrogation signal of an aircraft’s Traffic alert and Collision Avoidance System (TCAS) installation?

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Question 1 of 20

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🔍 Key Concepts

• Mode S / TCAS frequencies – which frequency is used for interrogations vs. replies? • Difference between directional (phased-array) and omnidirectional antenna patterns. • How a ground radar/ground station typically sends signals to determine aircraft direction.

💭 Think About

• First, recall which frequency (1030 MHz or 1090 MHz) is used for sending interrogation signals and which is used for aircraft replies in Mode S/TCAS systems. • Next, think about what a phased-array antenna is designed to do: does it radiate equally in all directions, or does it form steerable beams? • Since the question specifies a ground station and directional antenna, ask yourself whether a radar-like system would more likely use a narrow beam or an all-around pattern for interrogations.

✅ Before You Answer

• Verify which frequency is associated with interrogation (uplink) and which with reply (downlink) in Mode S/TCAS (1030 vs 1090 MHz). • Confirm that a phased-array system is used to create a directional (beam-shaped) rather than omnidirectional pattern. • Match the correct frequency–pattern pair: the option should combine the interrogation frequency with a directional pattern.

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