A low-noise time-domain EMI measurement system for measurements up to 26 GHz

In this paper, a low-noise time-domain EMI measurement system for the frequency range from 9 kHz-26 GHz is presented. It combines ultra-fast analog-to-digital-conversion and real-time digital signal processing on a field-programmable-gate-array (FPGA) with ultra-broadband multi-stage down-conversion. By using low-loss components, the system noise floor power spectral density is decreased to below -150 dBm/Hz, yielding an ultra-low noise floor of typically below -115 dBm with a 9 kHz IF-filter. The high system sensitivity allows for the characterization of broadband, low-level signals near the noise floor, like ultra-wideband (UWB) communication. Defected ground structures increase the return loss of the low insertion loss SP5T PIN-diode switches. The system IF dynamic range exceeds the requirements of CISPR 16-1-1 by over 20 dB and allows for the measurement of high-dynamic range signals like radar pulses. Scan time is decreased by several orders of magnitude. A scan from 9 kHz to 26 GHz with a 9 kHz IF-filter bandwidth is completed in under 200 s, while over 5-10⁶ frequency points are calculated.