Embodiments of an apparatus for minimizing oscillation of an amplifier in an antenna system are provided. These embodiments can comprise passive circuitry in the form of a coupling simulator that includes passive elements selected and combined to generate an output with properties that can cancel or substantially reduce a coupled input as between two antennas in the antenna system. In one example, the coupling simulator may include a phase-shifting device and an attenuating device, each of which have properties with values selected based on parameters that result from the relationship between the antennas of the antenna system.