A broadband, low-noise time-domain system for EMI measurements through K_a-band up to 40 GHz

In this paper, a time-domain EMI measurement system for the frequency range from 10 Hz to 40 GHz is presented. Signals with a frequency of up to 1.1 GHz are sampled by an ultra-fast floating-point analog-to-digital-converter (ADC) and processed in real-time on a field-programmable-gate-array (FPGA). An ultra-broadband multi-stage down-converter allows for the measurement of signals with frequencies up to 40 GHz. Measurement times can be reduced by several orders of magnitude compared to traditional EMI-receivers that work in frequency-domain. With preselected integrated low-noise amplifiers, the system offers high sensitivity especially in the K_a-band from 26.5 GHz to 40 GHz. The low system noise figure from 26.5 GHz to 40 GHz yields an average noise floor level of around 12 dBμV using an IF-filter bandwidth of 1 MHz in this range. With a high system dynamic range of more than 70 dB, the system is excellently suited for the measurement of broadband, transient emissions or high-dynamic signals like radar pulses. Non-stationary emissions can be measured via the real-time spectrogram or via the multi-channel amplitude probability distribution (APD) measuring method.