I realize the subject line pertains to PSA series, but the discussion started here and seems relevant. If moderator has better suggestion for placing this question, please advise.
Have a similar question, except for the HP 8563E/EC series, which have N connector input, 26.5 GHz max frequency, and option 026 available (3.5mm connector.) I selected N input (no option 026) for connector mechanical ruggedness, but will have measurements up to at least 24 GHz.
1. I presume I should adapt front panel input to 3.5mm (rather than using N all the way to DUT) for measurements > ~18 GHz - correct?
2. What degredation in specificied amplitude accuracy and/or input return loss should be expected with this method (adapt at front panel to 3.5mm interface)?
3. Should I specify a particular N(m)/3.5mm adapter (Agilent part number 1250-1744, for example?)
4. Can the non-026 model be retrofitted in a service shop to 026 by changing the front panel connector (if so, what part number)?
Excellent question. N-type industry connectors generally work only up to 18 GHz, but still E4440A that goes up to 26.5 GHz has an N-type connector.
The concern is that a Type-N connector would introduce modes in the Spectrum Analyzer frequency response. A mode occurs when the Type-N connector structure becomes a weakly resonant cavity. This resonance would appear as a very narrow band suckout in the connector insertion loss. This mode would presumably not be corrected by the Spectrum Analyzer flatness calibration.
Behind the Spectrum Analyzer front panel the internal cabling is 3.5 mm. The Type-N front panel connector is simply a Type-N (f) to 3.5 mm (f) adapter. So, any moding would be attributable to the Type-N input adapter. Modes do not occur in Agilent Spectrum Anayzers for several reasons.
Advances in precision machining have allowed Type-N connectors to operate mode-free to 26.5 GHz. The PSA Type-N adapter shares many characteristics with the Agilent 1250-1745, Type-N (f) to 3.5 mm (f) adapter. Take for instance the Agilent 1250-1745 3.5 mm (f) to Type-N (f) adapter. The inner shield of the Type-N connector is solid. General purpose Type-N adapters (the Agilent 1250-1778 for instance) have a slotted inner shield. The slots allow for mechanical tolerance variations, however they create a non-uniform ground plane on the inner shield. The slots can lead to fringing of the E-field. These fringing effects impact connector performance.
Another area where Agilent has contributed to connector performance is in the center conductor support bead. Older Type-N adapters have Delron, or PTFE supporting the inner conductor. Looking into a general purpose Type-N adapter one can see a white dielectric surrounding the center conductor. The 1250-17XX family of Type-N adapters have a black support structure. This black support bead is an Agilent patented material that suppresses modes.
One simple test to look for modes can be done by mating an Agilent 1250-1744 (Type-N (m) to 3.5 mm (f)) and a 1250-1745 (Type-N (f) to 3.5 mm (f)). The insertion loss of the assembly can be measured with a network analyzer. The measurements should be made over a very narrow bandwidth stepping from 18 GHz to 26.5 GHz. Any modes will appear as a notch in the S21 response. Extensive testing on a PNA Network Analyzer with many connector combinations has shown the 1250-17XX family to be mode free.