Electromagnetic Compatibility Testing between LDACS and Surveillance Transponder

The L-band digital aeronautical communications system (LDACS) is a broadband, secure digital communications system based on cellular technology, designed specifically for aeronautics applications. It enhances the safety and efficiency of air traffic management (ATM) by supporting innovative paradigms such as 4D trajectory-based operations (TBO). Given that the LDACS frequency band is also allocated for aviation surveillance and navigation equipment, ensuring electromagnetic compatibility (EMC) with these systems is critical. The determination of requirements for collocating LDACS and aeronautical surveillance systems in L-band has already started, recently. However, realistic and solid measurement findings are necessary to determine the condition for co-existence. This study investigates the EMC between LDACS and surveillance transponder (XPDR) to establish the required attenuation levels for their onboard coexistence. Two transponders are used as devices under test (DUT): one tailored for small aircraft and the other for large aircraft. Through a combination of experimental analysis and estimations, the study identifies the attenuation levels necessary for LDACS-XPDR coexistence. These findings enable the implementation of measures such as antenna separation or out-of-band rejection filters to facilitate the effective integration of LDACS and XPDR onboard aircraft.