Dependence of peak power measurement of ultra wideband signals on impulse bandwidths of spectrum analyzers

Emission levels of ultra wideband (UWB) devices are regulated, since they overlay incumbent wireless spectrum users while ensuring sufficient attenuation to limit in-band interference. Spectrum analyzers (SAs) are usually used to measure average and peak power spectra. Whereas the average power is measured in a 1-MHz resolution bandwidth (RBW), the UWB peak power is defined in a 50-MHz RBW, according to an FCC regulation and an ITU-R recommendation. Most of the SAs, however, are not equipped with the 50-MHz RBW. Hence the power spectrum measured in a narrower RBW must be converted into the peak power spectrum in the 50-MHz RBW, but the conversion formula has not been well established. The RBW is defined with an impulse bandwidth (IBW) for peak power measurement in CISPR Publication 16-1-1, but most SAs do not strictly follow the CISPR definition. In this paper, the IBWs of five different SAs were measured by using an impulse signal. Then the three different UWB signals were measured in a 1-MHz RBW with the five SAs, and the power spectra were converted into 50-MHz peak power spectra using conventional and new formulas. These UWB signals were also measured with a digital storage oscilloscope and then Fourier-transformed into 50-MHz-RBW spectra. The new formula using IBW instead of RBW yielded the consistent peak power spectra, which were found to be independent of SAs and to agree with the oscilloscope measurements.