Attenuation band impedance matched BRF for measurements of electromagnetic noise

Wireless communication devices such as wireless LANs and RFIDs are essential for smart home appliances and IoT (Internet of Things) devices in Smart Cities. When measuring the high-frequency noise generated by devices, wireless signals of wireless communication devices and high-frequency noise are measured at the same time. As a result, spectrum analyzers have insufficient dynamic range, or the excess signal from wireless communication devices causes harmonic distortion of the mixer inside the receiver, resulting in inaccurate measurements. Accordingly, a band rejection filter (BRF) is required to attenuate the radio signal. CISPR 16-2-3:2016+A1: 2019 assumes that impedances are matched for measurement, so if the impedance mismatch is large, the expanded uncertainty specified in CISPR 16-4-2:2011+A1:2014+A2:2018 increases. In this study, we propose a new BRF with impedance matching in the attenuation range and show its principle. As a result, the extended uncertainty could be reduced to 3.96 dB for the BRF of this study compared to 10.63 dB for the conventional BRF. In addition, the method comparison of CISPR 16-2-3:2016+A1: 2019 and vector network analyzer shows that the difference in attenuation of the conventional BRF was about −0.8 to 3.3 dB, whereas the BRF in this study were about −0.2 to 0.3 dB. The reduction of the expanded uncertainty and the good measurement results confirm the high usefulness of the CISPR 16-2-3 measurement system for the measurement of weak electromagnetic noise.