What type of antenna is used in an aircraft's Instrument Landing System (ILS) glideslope installation?

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Multiple Choice

What type of antenna is used in an aircraft's Instrument Landing System (ILS) glideslope installation?

The glideslope signal is in the UHF range (around 330 MHz) and is received by a simple, broadband element on the aircraft. A folded dipole is well suited for this frequency because it provides a compact, efficient receiving element with an impedance that can be matched easily to 50-ohm coax using a balun. Its two-wire folded design gives broad bandwidth to cover the glideslope carrier and its modulation components without requiring complex or moving parts. This keeps the installation lightweight and reliable on the aircraft while still picking up the ground-based glideslope signal from the runway area. Other antenna types would either be unnecessarily complex for this purpose (an electronically steerable phased array) or not match the typical reception requirements and polarization of the glideslope signal. A vertically polarized omnidirectional pattern or a balanced loop would not offer the same practical combination of size, impedance match, and reception performance for the UHF glideslope frequency.

The glideslope signal is in the UHF range (around 330 MHz) and is received by a simple, broadband element on the aircraft. A folded dipole is well suited for this frequency because it provides a compact, efficient receiving element with an impedance that can be matched easily to 50-ohm coax using a balun. Its two-wire folded design gives broad bandwidth to cover the glideslope carrier and its modulation components without requiring complex or moving parts. This keeps the installation lightweight and reliable on the aircraft while still picking up the ground-based glideslope signal from the runway area.

Other antenna types would either be unnecessarily complex for this purpose (an electronically steerable phased array) or not match the typical reception requirements and polarization of the glideslope signal. A vertically polarized omnidirectional pattern or a balanced loop would not offer the same practical combination of size, impedance match, and reception performance for the UHF glideslope frequency.

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