Some embodiments of the present invention provide a system that characterizes a computer system parameter by analyzing a target electromagnetic signal radiating from the computer system. First, the target electromagnetic signal is monitored using a first antenna and a second antenna, wherein an axis of the second antenna is oriented non-parallel to an axis of the first antenna. Then, the target electromagnetic signal received from the first antenna and the target electromagnetic signal received from the second antenna are separately analyzed to characterize the computer system parameter.