Post subject: about RF connectors/adaptors Posted: Fri Jun
30, 2006 7:53 pm
Joined: Tue Apr 18, 2006 10:40
hello....i'm new to using RF lab equipment so i've
a basic question...
an N-connector has cutoff frequency of ~11
GHz and SMA ~25 GHz. when an N-to-SMA adaptor is used, what's meant
by this? That the cutoff frequency moves upto 25 GHz, meaning there
will be 50 ohm match upto 25 GHz?
or the cutoff frequency is
11 GHz after using this adaptor? i don't think it will be 11 GHz. for
one, i've two pieces of equipment that say in their manuals that they're
compatible w/ each other but one has N connector and the other has SMA/3.5
mm connector because it operates upto 26.5 GHz---so i'd thinkt he cutoff
will be around 26 GHz and not 11 GHz (for N) otherwise the two equipment
are not completely compatible. thanks
Post subject: Posted: Wed Jul 05, 2006 10:27 am
Joined: Thu Apr 13, 2006 9:53 am
The cutoff freq of a standard N connector is 11 GHz whereas a precision
N is 18 GHz. The cutoff freq of a standard SMA is 18 GHz and a 3.5mm
is 26.5 GHz. These values are for connecotrs made to the MIL standard.
Many manufactures control the machined tolerance much better than defined
in the MIL spec so they can boost the frequency performance of there
version to a higher frequency range (SMA to 22-26GHz vs 18GHz from a
"standard" for example).
The frequence range of a between series
adapter (N to SMA etc.) is limited to the frequency range of the lowest
type's freq range. In a standard N to SMA the freq range is limited
to 11GHz ortherwise moding can occure and for sure it will have higher
loss at freq above 11GHz. The actual loss will have to be measured since
it woun't be specified on any spec sheet. This is also true of cables
made with sifferent series connectors.
best source of info are
the App-notes from M/A-Com, Maury Microwave and other connector Mfgr.
Also look for connector design articles in back issues of RF Design,
Hope this helps
Post subject: about RF connectors/adaptorsPosted:
Thu Jul 06, 2006 5:37 am
Joined: Fri Feb
17, 2006 12:07 pm
Location: London UK
I can't add
much more to what RFTEJerry has said, except a note about the cables
to which the connectors are attached.
A coaxial cable to which the
N type is attached (and even the connector) will contain dielectric
insulation. This means that a typical 12 to 15mm diameter (id) coax
cable will have a set of performance parameters that include Reflection
Coefficient and loss attenuation (S11 and S21).
There is a non-TEM
waveguide mode that can be set up in a coaxial structure, and I think
this can propagate at frequencies above about 7GHz. The effect of the
dielectric insulation is that the lowest cut off frequency for the rogue
non-TEM mode is lower than the 11GHz stated.
If these are present
in one part of the system, the part terminated in the N-type, then when
they encounter the transition to a much smaller cross section coax (the
SMA part) they encounter quite a high Ref Coeff. Thus the combination
of 2 different cable sizes and a BSA type adapter imposes a Ref Coeff
spec that sets the frequency of application to a max of around 11GHz.
A lot depends on how bad an S11 spec you can live with
Post subject: Posted: Sun Jul 09, 2006 1:45
Joined: Tue Apr 11, 2006 8:13 pm
Most test equipment (spectrum analyzers, VNA's) that I have worked
with have an N-connector, even though they are meant to be used at frequencies
way above the cut-offs mentioned in the previous posts. How much of
an impact would that have on the measurements?
Post subject: Posted: Sun Jul 09, 2006 3:49 pm
Joined: Thu Apr 13, 2006 9:53 am
The Type-N connector on the spectrum analyzer
will handle the frequency range of the analyzer with the loss and VSWR
accuracies specified by the instrument manufacture.
reference a Type-N, SMA, 3.5mm it is understood to be the standard MIL-SPEC
connector and it will be limited to the MIL-SPEC frequency range. A
connector mfg can make a mechanically equvialent connector with an extended
freq range by having the manufactured dimentions and tolerance more
precisely controlled. Any connectors frequency range is controlled by
its mechanical dimensions and the dielectric, if used. A 3.5mm does
not have a dielectric so it can go to 26.5GHz whereas the SMA can only
go to 18GHz (it has a dielectric), but they can mate. Many instrument
manufacturets and cable manufacturers also make their own versions of
Type-N and SMA connectors just so they can use them on their instruments
and cables at extended frequencies.
Visit connector mfg and cable
mfg web sites and read their App notes. They will explain just how they
are able to extend the freq range of a Type-N from 11GHz to 18GHz and
the SMA from 18GHz to 26GHz.
I know this can be confusing because
it was to me when I first started in RF test. But after researching
and reading it became clearer.