Relationship Between the Transponder Triggering Area and the SSR Mode S Surveillance Coverage Map

EUROCONTROL and other European organizations place great emphasis on the efficiency of the use of the radio frequency band 1030/1090 due to its heavy load. One of the major contributors to the load on this band is the excessive number of replies that aircraft emit as a result of “Mode S Only All Call” interrogations from SSR Mode S radars. The dominant source of these replies is the area that arises between the end of the radar's surveillance coverage map to the border where transponder minimum triggering level (MTL) is achieved. Therefore, it should be an effort that the interrogation power is optimally adapted to the set surveillance coverage map and is not unnecessarily greater. Based on the processing of replies from aircraft, the paper analyzes how large this area is and whether there is a clear relationship between the set size of the surveillance coverage map and the so-called physical range of the radar. The aim is to find out how manufacturers and air navigation service providers (ANSPs) approach this setting. The paper uses data available from the Open Sky Network portal, and the analysis is performed on a sample of selected SSR within the European region.