Limitations of SMA Coaxial Connectors
Common coaxial connector standards can be found throughout the RF/microwave industry for between/inter system, between/inter module, and even between/inter component interconnects. One of the most common types of coaxial connectors are SMA Connectors. This coaxial connector standard is used in test and measurement, consumer RF/microwave, radar/sensing, telecommunications, and most other low power and low to high microwave frequency applications.
It is not uncommon to see SMA connectors on test and measurement equipment or between critical modules in high performing RF sensing apparatus. However, SMA coaxial connectors have a variety of limitations. These limitations may not be apparent as common SMA connectors can often be found in the “sweet spot” of cost and performance which are why SMA connectors are so widely used. These connectors have power, frequency, VSWR, accuracy, size, insertion loss, and issues related to their popularity and sourcing that can ultimately lead to challenges for engineers relying heavily on SMA connectors.
There are specialty SMA connectors that deviate from the standards and feature enhanced performance areas. These specialized SMA connectors often come with trade-offs, though cost and size are some of the most common. For instance, there are high voltage (HV) (though not common), high power, precision, hermetically sealed, non-magnetic, and other specialty variants of the standard SMA connect. These specialty types tend to be more expensive, require less common materials, likely aren’t available in the same quantities as more common SMA variants, and may not be available in certain configurations, such as end-launch or with certain cable attachment methods. For example, high voltage and high power SMA variants are most likely available with specific attachment methods that coincide with specialty coaxial cable to maintain the enhanced performance capabilities these connectors are designed for. These specialty connectors may also not be compatible with widely available SMA Adapters, and require specialty adapters or may not be compatible with adapters at all.
The original SMA connectors were typically only specified to 12 GHz, though most common SMAs today are rated to 18 GHz. There are variants that are available that operate to 26.5 GHz or even 30 GHz, otherwise known as high precision SMA connectors. These connectors, even precision variants, aren’t ideal for many millimeter-wave applications, even if the connectors have the frequency capability. That is because the basic design of an SMA connector has mechanical precision limitation, and a dielectric spacer is needed. Hence, the loss through these connectors at millimeter-wave frequencies tends to be higher than with “millimeter-wave” rated coaxial connectors.
