A communication apparatus for a high-altitude platform, HAP, the communication apparatus comprising: a transmitter configured to generate a radio frequency, RF, signal; a primary antenna system configured to generate an RF beam based on the RF signal, the primary antenna system including: a first plurality of antenna elements, a first power divider having an input in communication with the transmitter, and a plurality of outputs, and a nulling activation switch having a first contact (437 1) a second contact (437 2), and a third contact (437 3); and a detachable nulling subassembly that is configured to attach to and detach from an interface of the primary antenna system and is in communication with the nulling activation switch via the interface, wherein the detachable nulling subassembly is configured to modify the RF beam generated by the primary antenna system by generating nulling signals when the nulling activation switch is controlled to feed the RF signal to an input of the detachable nulling subassembly, wherein the detachable nulling subassembly includes: a second power divider having an input and a plurality of outputs and configured to receive the RF signal from the second contact (437 2), a plurality of phase shifters, and a plurality of nulling antenna elements; the transmitter is in communication with the first contact (437 1) of the nulling activation switch; the RF signal is fed to the input of the second power divider when the nulling activation switch is closed such that the first contact (437 1) is connected to the second contact (437 2), and each output of the second power divider feeds the RF signal to a respective processing chain including one of the plurality of the phase shifters connected in series with one of the plurality of the nulling antenna elements; and the RF signal is fed to the input of the first power divider when the nulling activation switch is closed such that the first contact (437 1) is connected to the third contact (437 3), and each output of the first power divider feeds the RF signal to a respective one of the first plurality of antenna elements. a transmitter configured to generate a radio frequency, RF, signal; a primary antenna system configured to generate an RF beam based on the RF signal, the primary antenna system including: a first plurality of antenna elements, a first power divider having an input in communication with the transmitter, and a plurality of outputs, and a nulling activation switch having a first contact (437 1) a second contact (437 2), and a third contact (437 3); and a first plurality of antenna elements, a first power divider having an input in communication with the transmitter, and a plurality of outputs, and a nulling activation switch having a first contact (437 1) a second contact (437 2), and a third contact (437 3); and a detachable nulling subassembly that is configured to attach to and detach from an interface of the primary antenna system and is in communication with the nulling activation switch via the interface, wherein the detachable nulling subassembly is configured to modify the RF beam generated by the primary antenna system by generating nulling signals when the nulling activation switch is controlled to feed the RF signal to an input of the detachable nulling subassembly, wherein the detachable nulling subassembly includes: a second power divider having an input and a plurality of outputs and configured to receive the RF signal from the second contact (437 2), a plurality of phase shifters, and a plurality of nulling antenna elements; a second power divider having an input and a plurality of outputs and configured to receive the RF signal from the second contact (437 2), a plurality of phase shifters, and a plurality of nulling antenna elements; the transmitter is in communication with the first contact (437 1) of the nulling activation switch; the RF signal is fed to the input of the second power divider when the nulling activation switch is closed such that the first contact (437 1) is connected to the second contact (437 2), and each output of the second power divider feeds the RF signal to a respective processing chain including one of the plurality of the phase shifters connected in series with one of the plurality of the nulling antenna elements; and the RF signal is fed to the input of the first power divider when the nulling activation switch is closed such that the first contact (437 1) is connected to the third contact (437 3), and each output of the first power divider feeds the RF signal to a respective one of the first plurality of antenna elements.