Convergence of Shielded Room Error Analysis Using Image Antenna Theory

The near-zone magnetic field radiated by a small-loop antenna has been used for the sensitivity test of a radio receiver. When an external interference field exists around the antennas, the test must be carried out in a shielded room. The formulas to estimate the effect of the room on the standard magnetic field are derived by using the image antenna theory. These formulas are expressed in the form of an infinite series. The states of the convergence of the formulas are compared with those already derived from the reciprocity theorem. The convergence for the image antenna theory is more rapid when the ratio of the loop spacing to the wavelength is smaller and the ratio of the size of the shielded room to the wavelength is larger, while the one for the reciprocity theorem is more rapid under reverse conditions.