Linear Dynamic Range Analysis of the Circuit in EMI Near-Field Scanning System

In a near-field scanning system, the electric and magnetic field above device under test (DUT) can be obtained from the measured voltage with system factor (SF). The SF is defined as the complex-valued frequency-dependent ratio of the simulated field strength at the location of the probe to the measured voltage, which includes the effects of the probe, cables and amplifiers. The nonlinearity of the measurement system will cause a distorted SF. To calculate the SF correctly, it is important to keep the signal level within the linear dynamic range of the measurement system. The formula for determining the linear dynamic range of a near-field scanning system is derived in this paper. The linear dynamic range of the system is defined as the range between the minimum detectable signal and the input 1dB compression point. The minimum detectable signal and the input 1dB compression point of the system are affected by the noise figure, gain and 1dB compression point of amplifiers and cables. The formula for the linear dynamic range can also give a guidance for the design of a near-field scanning system.