What type of antenna is attached to a Mode C transponder installation and used to receive 1030 MHz interrogation signals from ATCRBS?

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Multiple Choice

What type of antenna is attached to a Mode C transponder installation and used to receive 1030 MHz interrogation signals from ATCRBS?

1030 MHz is the uplink frequency used by ATCRBS to interrogate aircraft transponders. The transponder needs to hear those interrogations from any direction as the airplane travels, so the antenna must provide nearly 360-degree coverage in the relevant plane. An L-band monopole blade-type omnidirectional antenna is designed for this purpose: it’s compact, mounted on the aircraft, and offers uniform reception from all directions in the L-band. Other designs like a steerable phased array are unnecessarily complex and bulky for typical aircraft installations, a folded dipole isn’t the standard form used for this uplink, and a mechanically rotatable loop is more about directional sensing than the simple uplink reception required here.

1030 MHz is the uplink frequency used by ATCRBS to interrogate aircraft transponders. The transponder needs to hear those interrogations from any direction as the airplane travels, so the antenna must provide nearly 360-degree coverage in the relevant plane. An L-band monopole blade-type omnidirectional antenna is designed for this purpose: it’s compact, mounted on the aircraft, and offers uniform reception from all directions in the L-band. Other designs like a steerable phased array are unnecessarily complex and bulky for typical aircraft installations, a folded dipole isn’t the standard form used for this uplink, and a mechanically rotatable loop is more about directional sensing than the simple uplink reception required here.

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