［ポスター講演］UWBピーク電力測定におけるスペクトラムアナライザの機種依存性

摘要

Spectrum analyzers (SAs) are usually used to measure average and peak power spectra of ultra wideband (UWB) signals. Whereas the average power is measured in a 1-MHz resolution bandwidth (RBW), the UWB peak power is defined in a 50-MHz RBW. 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 report, the IBWs of seven different SAs were measured by using an impulse signal. Then the three different UWB signals were measured in a 1-MHz RBW with the seven 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.%UWB信号のピーク電力をスペクトラムアナライザ（SA）によって測定する場合に問題となる，SA機種によるインパルス帯域幅（IBW）の違いと，スペクトルの50MHz帯域幅への換算の妥当性について実験的に検討したUWB信号のピーク電力は帯域幅50MHzで測定することと規定されているが，市販のスペクトラムアナライザには分解能帯域幅（RBW）を50MHzに設定できるものはほとんどないため，50MHzに換算する必要がある．この換算には本来SAのIBWを用いなければならないが，必ずしもRBW＝IBWではない．7機種のSAについてIBWはRBW＝1MHzの場合において0ないし＋60％程度のばらつきがあることを明らかにした．実測したIBWに基づく換算式を用いればRBW＝50MHzに換算したスペクトルはオシロスコープで測定した時間波形をFFTしたものと概ね一致した．また，最大ピーク電力およびRMS誤差も概ね1dB以内に収まった．