Thread: PSA 4440A: Can the N connector work upto 26.5GHz?


Permlink Replies: 5 - Pages: 1 - Last Post: Apr 24, 2012 12:44 PM Last Post By: dichheda
stewart_lee

Posts: 12
Registered: 06/11/07
PSA 4440A: Can the N connector work upto 26.5GHz?
Posted: Dec 28, 2007 10:26 PM
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I recalled in some HP app notes said that the inner conductor supporting bead of a N connector will absorb/resonate at some dedicated frequencies around 19GHz. Which make the N connector not suitable for the metrology grade measurements upto 20GHz. But the 4440A still uses N connector for the input, does the supporting bead's performance have been improved or there is other reason to use N instead of 3.5mm?

Thanks.
dichheda

Posts: 36
Registered: 01/04/07
PSA 4440A: Can the N connector work upto 26.5GHz?
Posted: Jan 3, 2008 7:00 PM   in response to: stewart_lee in response to: stewart_lee
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Hello Stewart,

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.
stewart_lee

Posts: 12
Registered: 06/11/07
PSA 4440A: Can the N connector work upto 26.5GHz?
Posted: Jan 3, 2008 7:31 PM   in response to: stewart_lee in response to: stewart_lee
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Thank you very much for the details, this makes me feel confident of the measurement fedility.
dgun

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Registered: 12/12/05
PSA 4440A: Can the N connector work upto 26.5GHz?
Posted: Jan 15, 2008 10:58 AM   in response to: stewart_lee in response to: stewart_lee
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Although the instrument connectors may be mode free, moding will still occur if the DUT or external cabling uses N-type connectors or cables that are not mode free.
dichheda

Posts: 36
Registered: 01/04/07
Re: PSA 4440A: Can the N connector work upto 26.5GHz?
Posted: Sep 28, 2009 8:17 PM   in response to: stewart_lee in response to: stewart_lee
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Correction from my previous reply:

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 suck out 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.

In my previous reponse, I mentioned that the N-type adapter 1250-1745 was mode free up to 26.5 GHz. I stand corrected. 1250-1745 is specified only up to 18 GHz and could show moding above that. As mentioned above, the PSA input connector has a 3.5 mm cabling behind it and so any moding would be attributable to the Type-N input adapter.

Dipti
dichheda

Posts: 36
Registered: 01/04/07
Re: PSA 4440A: Can the N connector work upto 26.5GHz?
Posted: Mar 12, 2012 12:08 AM   in response to: dichheda in response to: dichheda
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Our latest family of analyzers are the X-Series signal analyzers. This includes PXA, MXA, EXA, and CXA, in order of performance. The issue of modes in Type-N connectors is only relevant to analyzers ordered with frequency option 526 (26.5 GHz) because those ordered with higher frequency options do not have type-N connectors, and those ordered with lower frequency options do not operate in the frequency range (18 to 26.5 GHz) that can have modes in the Type-N connector.

Analyzers with frequency option 526 available (PXA, MXA and EXA) will not be subject to modes if they are fitted with a 3.5 mm input connector. This fitting is option C35 in PXA and is also available through special handling in MXA and EXA.

There are nominally six modes in the frequency range of 18 to 26.5 GHz. For general amplitude accuracy, the effect of these modes with this connector is included within the specifications as part of frequency response.

For IF frequency response (which is relevant to demodulation and FFT response relative to the center frequency) and IF phase linearity, the effect of the modes is not included within the specifications and must be added as an additional error term to error budgets for analysis in the modes frequency region. These modes cause nominally up to −0.35 dB amplitude change, with phase errors of nominally up to ±1.2°.

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