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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 mm connectors
2.4 and 1.85 mm connectors
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 sleeve.
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 radials.
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.
3.5mm and 2.92 connectors
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.
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3.5 mm connector (male)
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2.92 mm connector (male)
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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!
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2.4 mm connector (male)
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1.85 mm connector (male)
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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!
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1 mm connector (female)
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1 mm connector (male)
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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.