Constant near-field gain for a shielded loop antenna operated in the liquid at 30 MHz

For calibrating electric-field probe to evaluate the value of SAR (specific absorption rate) for devices at a frequency of 30 MHz, a shielded loop antenna is used as a reference antenna. To facilitate curve fitting for the calibration, near-field gain should be constant near the loop. In this paper, it is shown that the circumference of the loop can be selected as the near-field gain becomes approximately-constant near the loops.