Updated October 30,
here to go to our main page on microwave connectors
here to go to a page on how (not) to trash a cal kit!
Attention starving connector
vendors, you can contribute and sponsor
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By precision, we mean expensive...
Note that with the exception of 7mm, all of these connectors use
an air dielectric.
7 mm connectors
3.5 and 2.9
2.4 and 1.85
1 mm connectors
7 mm connectors
The lowest VSWR of any connector
offered, 7 mm connectors work well up to 18 GHz. The unique thing
about 7 mm connectors is that they are sexless. Each connector can
act as either a "male" or a "female", depending
on which way you spin the coupling nut. Looking into the connector,
if you spin the coupling nut clockwise, the coupling sleeve will
extend, and the connector becomes female, spin it counterclockwise
and it retracts and becomes male. OK, we just violated our definition
of what makes a connector male or female, which is generally the
configuration of the center conductor. The center conductor as well
as the contact surface of the outer conductor of 7 mm connectors
are always the same, so we have to refer to the sex of the outer
7 mm connectors are big enough
so that they don't need a wrench to tighten and loosen them. You
should be able to tighten (and loosen) them by hand. Of course,
there is always some gorilla in the lab that can tighten a 7 mm
connector so hard that no one else can get it loose. Fortunately,
most 7 mm connectors have hex-nuts that fit a 3/4 inch wrench. Don't
you just love how the microwave industry has hopelessly mixed up
the English (SAE) and metric (SI) systems? Almost as bad as the
tire industry with their 165 (centimeter) SR-14 (inch) steel-belted
One common mistake that people
make with 7 mm connectors is that after they tighten one connector
to the other, they tighten both coupling nuts against each other.
This is just wrong! Tighten only the coupling nut that that does
not have its coupling sleeve extended, and leave the other one
loose, flapping in the breeze.
These three connector styles
use air dielectric, and will mate with each other as well as the
cheaper SMA styles. The 3.5 mm connector is the next upgrade from
using SMA, it performs well up to 26 GHz. The 2.92 mm connector
(often called simply "2.9 millimeter") works up through
40 GHz. The K-connector is Anritsu's version of the 2.92 mm connector.
As you can see from the pictures
below, the outer diameter of the coax decreases slightly from 3.5
to 2.92 mm coax. After a while you will be able to identify the
different species of connectors by looking into them to see the
relative sizes of the outer diameter.
There's some great photos of
3.5 mm connectors on our how (not)
to trash a cal kit page.
2.4 mm and
1.85 mm connectors
The 2.4 and 1.85 connectors are
mechanically compatible with each other, but neither one will thread
onto an SMA, 3.5 or 2.92 mm connector. This is on purpose, so you
won't mix these expensive connectors in with less precise connectors
such as SMA and cause them irreparable harm.
The 1.85 connector is often called
the "V connector". Both the 2.4 and 1.85 mm connector
require a 5/16 inch wrench.
The price keeps climbing as you
go up in frequency. A V-connector can cost $500!
1 mm connectors
The 1mm connector is the highest-frequency
millimeterwave connector on the market. It performs up to 110 GHz.
A single 1mm connector can cost $1000!
These pictures of 1mm connectors
were contributed by Keith, who works for a big company that was
once even bigger and known as simply "HP". These are photos
of offset shorts from a calibration kit. Thanks, guy!
It's hard to tell the difference
between 1mm and 1.85 mm! Here's some comments from Keith about that...
Is the center pin of 1mm
reduced in diameter? It’s an optical illusion. The camera is picking
up the very tip, but the tapered lead-in looks absent. Then there’s
the shoulder of the male pin, and then air. Perhaps a camera shot
at an angle would work better.
The 1 mm connector is proportionally
similar to 2.4. The center conductor diameter on the 1.85 is reduced
compared to the 2.4 (0.803 mm vs. 1.042 mm), but the mating pin
is the same size. Thus, the step between the mating pin and the
center conductor OD is smaller on the 1.85. The soft focus on
the 1.85 mm connector photo makes it hard to see the detail on
the center conductor. All three connectors, 2.4, 1.85, and 1.0
were primarily designed by Julius Botka, now retired. They exhibit
his preference for beefy outer conductors that align before the
center conductors mate.