close and far conductors affect receiving antenna pattern

im simulating a spiral receiving antenna in freq. range 2-18Ghz.
the antenna is placed closed to several metal conductors, and i want to simulate the radiation pattern of antenna. i want to know which one of the closed materials(metals) should be considered in simulation. i mean if we want to neglect some conductors near the antenna , how much it should be far from antenna(in wavelength)?


thank you very much.