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The SMA connector is probably the most popular connector of all the RF coaxial cable connectors out there. Its popularity is due to its many valuable qualities such as :
However with all the varieties out there, there needs to be major considerations on the differences that many of the manufacturers offer. These differences although subtle can make for massive performance differences and can easily make a working reliable system into one that is malfunctioning or performance crippling simply by changing from one part to another.
The first consideration is the connector physical size. Although all SMA connectors are supposed to be designed to MIL-PRF-39012:
https://www.svmicrowave.com/rf-series/sma
The aperture for the SMA connector is relatively large at 4.6 mm for up to 18 GHz :
https://www.showmecables.com/blog/post/sma-dimensions
As the aperture get smaller the ability of the connector to handle larger frequencies also gets higher in performance, therefore 26.5 GHz SMA connectors will have much smaller aperture diameters than 18 GHz varieties.
https://www.amtechs.co.jp/product/Inseries-SMA.pdf
In addition to that, the dielectric may also change to a very low PTFE (Teflon) dielectric as well. This will lower dielectric losses, especially for higher frequencies.
Materials and plating vary as well, from stainless steel, to brass, to aluminum, to other special alloys. The plating's are typically silver for lowest conductivity to gold for lowest contact corrosion, or nickel for low cost / low corrosion.
It's very important in an RF system that ALL SMA connections are matched in aperture diameter, dielectric materials, as well as frequency performance. In many cases it may make sense to stick with one manufacturer that has created standards and tolerances for their parts that will function as lab tested.
Using a 'mixed-bag' of SMA connectors is asking for trouble as many details, both published and unpublished, must be critically reviewed for compatibility. But even then only thru a through RF lab performance test can the differences be vetted out.
The problem is that all lab results are highly dependent on the connections chosen and therefore its a dog-chasing-its-tail problem of RF characterization.
To begin properly a VNA should be used for a same manufacturer of SMA connectors and that the instrument needs to be de-embedded for its own connections and losses. Next is that the basic plug and receptacle of the connectors for a single manufacturer need to be verified for losses. Then individual subsections and components need to be tested for characterization. Finally cable with SMA connectors need to be characterized for losses. All of these characterizations should add up properly and be in tolerance with the total system.
If you cannot afford to do all of this, at the very least is that you should know who is the manufacturer of the SMA connector to be able to match it. Many times parts and components come with SMA connectors that do not have visual indicators of the SMA connector manufacturer. It may be possible to get this information from the component or cable vendor, but if not there can be a visual inspection to see how closely the aperture and dielectric match from one SMA connector to another.
The real difficulty is the center pin size and alignment. The female pin is made to expand, but if there is not good co-planarity between pin and socket surfaces, high contact resistivity results as well as increased pin capacitance lowering overall RF performance.
So pay attention to the tiny details and it can save you big headaches in the long run, as well as getting maximum RF bang for the buck in your system !
For more background refer to the Wikipedia information :
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