Spectrum Analyzer specs, RBW and filter shape

[Alexei.Polkhanov]

In my previous post I had a question about Tracking Generator in Spectrum Analyzers. I think this is somewhat unrelated question so I decided to create new topic.

I was looking at spec sheets for different spectrum analyzers and I found myself in a usual deadlock - same parameter described in different terms by different manufacturers. I am talking about Agilent, Anritsu and R&S.

Most of specs have value for RBW, but Agilent provides value for "resolution filter shape" in form of a ratio. For example they explain that if minimal RBW is 3Hz then 15:1 ratio for resolution shape means that I will have a 45Hz resolution for signal 60db down. I understand that 5:1 mens better resolution. (will result in 15kHz in this case). Example of spec that provides this value: http://cp.literature.agilent.com/litweb/pdf/5990-5587EN.pdf. When I looked at one of Anritsu SA spec sheets I found nothing that resembles such parameter. For example this manual: http://www.anritsu.com/en-GB/Downloads/Manuals/User-Guide/DWL1922.aspx shows minimal RBW 10Hz but nothings regarding the filter shape.

Well 10Hz probably is not as good as 3Hz but still I am wondering if there is any way to derive filter shape parameters from Second Harmonic Distortion or other available value?