Where to find 26 GHz n-type adapters? Why does 26 GHz spectrum analyzer have n-t

[jplle]

I recently got a 8563E spectrum analyzer which is rated for 26.5 GHz. It has a n-type and connector on the front; yet I can't find any n-type to SMA adapters or any n-type connector that's rated above 18 GHz.

I read that the n-type connector is designed for 18 GHz and below. Why did HP put a N-type connector on a 26.5 GHz analyzer? Is there any place I can find a 26 GHz rated n-type connector that's not $1,000? Or will a 18 GHz connector be okay at higher frequencies?

[Brumby]

RF stuff is not cheap.  GOOD RF stuff is expensive.

This is one constraining factor for me - and why I look at the 1GHz region as the upper bound of my interest.

[SMB784]

RF stuff is not cheap.  GOOD RF stuff is expensive.

This is one constraining factor for me - and why I look at the 1GHz region as the upper bound of my interest.

I think its important to qualify what "good" means here.

Good enough is what is important.  Can your application tolerate a few dB of loss or does it need as close to 0 dB loss as possible?  If so, 18 GHz n-type connectors may be "good enough" for what you need to do.

The best RF stuff is going to be expensive because it has extremely well engineered specifications,  but you may not actually need that level of engineering.

Then there is the accuracy of the measurement instrument to consider.  Is your spectrum analyzer going to be accurate to less than 1dB?  Even for an excellent unit like the HP 8563E my guess is probably no.

So the more relevant question is what specifications does your intended application require?  Answer that, and then you will know what kind of connector you need.

[tggzzz]

I recently got a 8563E spectrum analyzer which is rated for 26.5 GHz. It has a n-type and connector on the front; yet I can't find any n-type to SMA adapters or any n-type connector that's rated above 18 GHz.

I read that the n-type connector is designed for 18 GHz and below. Why did HP put a N-type connector on a 26.5 GHz analyzer? Is there any place I can find a 26 GHz rated n-type connector that's not $1,000? Or will a 18 GHz connector be okay at higher frequencies?

An 18GHz will be OK to 26GHz, provided you define "OK" appropriately.

If you need accurate measurements at those frequencies, is an old and probably out of calibration analyser "OK"?

If you think N type adaptors are expensive, look at APC-7 adaptors - or any cable at 26GHz

[SilverSolder]

RF stuff is not cheap.  GOOD RF stuff is expensive.

This is one constraining factor for me - and why I look at the 1GHz region as the upper bound of my interest.

I'm the same, except I'm so cheap that 100KHz is my limit! 

[xmo]

Here is what Agilent had to say on the subject of 26 GHz type N connectors:

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 Teflon 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.

[jplle]

A few DB loss is no problem, but is this the only effect it's going to have?

This is a new realm for me, so I'm not sure what problems a18 GHz connector will present at 26 GHz. I guess that's my main question, what issues are likely to be caused by an 18 GHz connector.

My spectrum analyzer is being calibrated and aligned prior to me receiving it, accuracy is important to me.

For cabling, I was looking at megaphase cabling. For $100 or $200, you can buy a 3-ft mega phase cable That's rated for 100 GHz or more, seems too good to be true. Does anybody have experience with this brand?

[jplle]

@xmo

Thank you very much for your reply, this answers many questions.

[tkamiya]

I have a few megaphase cables.  They are very nice and flexible.  Cables rated for 100GHz as well as connectors for few hundred dollars is too good to be true, I think.

When it comes to HP using N type connectors for up to 26.5GHz, there is a note by HP basically saying whatever discrepancies you'll see is already included in specification.  At that kind of frequency, to claim any kind of accuracy, you'll have to go through a rigorous process of cleaning connectors and torquing up to right specifications, etc.  You'll also have a hard time finding any N terminated cables rated for 26.5 also.

Do you really need to go right up to the upper limit?

[antenna]

Check this out. Adapter chart at time 1:25.

[TheSteve]

If you stick with good quality adapters and connectors you're generally fine.

I just measured three different N female to female barrel adapters.

The last one is pretty terrible and is from some multi adapter set and was clearly never intended for anything above 12 GHz (many N connectors and adapters are rated only to 12 GHz).

Marker position indicates 18 GHz.

edit - added a pic of the test setup. Nothing too fancy, S21 path was normalized with N male to female adapters.

[Wuerstchenhund]

I recently got a 8563E spectrum analyzer which is rated for 26.5 GHz. It has a n-type and connector on the front; yet I can't find any n-type to SMA adapters or any n-type connector that's rated above 18 GHz.

I read that the n-type connector is designed for 18 GHz and below. Why did HP put a N-type connector on a 26.5 GHz analyzer? Is there any place I can find a 26 GHz rated n-type connector that's not $1,000? Or will a 18 GHz connector be okay at higher frequencies?

In general, the bog-standard N connector is rated for up to 11GHz only, however there are Precision N-types which are rated up to 18GHz (the 8562E and 8563E use such a Precision N connector).

Some of the Precision N connectors are rated to 26.5Ghz, however this isn't standardized and reliable measurements at that frequency depend on the whole transmission line using 26.5Ghz rated cables and connectors, which are even more expensive (and quite rare) than the already eye-watering expensive 18GHz variants. However, thanks to modern manufacturing standard many 18Ghz rated parts work fine up to 26.5GHz, too, but you'd have to confirm (e.g. through a VNA) to be sure.

Also, while regular N and Precision N are mechanically similar, using regular N connectors with a Precision N connector can cause damage in the precision part. That's why it's recommend to use a sacrificing adapter (such as a Precision N pass-through or a DC block) so the analyzer's Precision N connector is protected from damage. Which for a roughly a quarter of a century old 8563E might be a moot point, though.