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Agilent PN 894400-2 Measuring Phase Noise with the Agilent 89400 Series Vector Signal Analyzers Product Note The characterization of phase noise is increasingly 89410A dc-10 MHz vector signal analyzer important in modern communications systems. The 89410A has an input bandwidth of 0 to 10 MHz, In the past, it has been a very difficult and time- and intrinsically lower phase noise than other RF consuming measurement. The Agilent Technologies spectrum analyzers due to its baseband implemen- 89400 Series vector signal analyzers (VSAs) greatly tation. Practically, the instrument's input noise facilitate phase noise characterization measure- makes up the fundamental phase noise measure- ments for designers of systems with all but the most ment's dynamic range limitation, and will be dis- demanding requirements. The power of these vector cussed later. signal analyzers is in their ability to make very fast direct phase noise measurements in any The user needs to downconvert the signal-under- domain. For example, transmitter designers are test into the 0 to 10 MHz input bandwidth. The often interested in the actual spectral density phase noise bandwidth of interest dictates how around the carrier or inte-grated band power in close the carrier can be to either dc or 10 MHz. If adjacent channels, whereas users interested in the possible, the instrument should be phase locked to recovery of digitally modulated information may the signal-under-test, although it is not necessary. be most concerned with peak or RMS phase devia- tion of the recovered vectors. The 89400 Series VSAs 89440A dc-1.8 GHz vector signal analyzer quickly and easily produce results in any of these While most of the following discussion applies to domains. They are also capable of mathematically all the 89400 Series VSAs, some differences apply. locking to unlocked or drifting carriers, allowing The 89440A can directly measure input signals up fast and accurate averaged measurements even to 1.8 GHz. However, since the RF section is essen- under these conditions. This is a powerful feature, tially a heterodyned receiver, its local oscillator not available in other spectrum analyzers, that phase noise will reduce the phase noise measure- allows the recovery of close-in phase noise infor-