Given the task definition and input, reply with output. In this task, you are given a question and a context passage. You have to answer the question based on the given passage.

What negative is there to adapting an antenna's impedance?, Context: Resonant antennas are expected to be used around a particular resonant frequency; an antenna must therefore be built or ordered to match the frequency range of the intended application. A particular antenna design will present a particular feedpoint impedance. While this may affect the choice of an antenna, an antenna's impedance can also be adapted to the desired impedance level of a system using a matching network while maintaining the other characteristics (except for a possible loss of efficiency).
loss of efficiency