How Do I Choose SMA Connectors?

When choosing an RF connector, consumers must consider its electronic performance and its economic impact. Performance must meet the system wiring requirements, and the economy conform requirement for value engineering.

The rapid growth in “wireless” technology has also led to an increase in the number of RF connectors and associated cables. These assemblies serve as vital links between multiple circuit boards, antennas, and front ends and between power amplifiers and antennas. These assemblies are crucial for operating and maintaining wireless devices and networks such as cellular telephones, wireless-data networks, advanced radar, and electronic-warfare systems (EW).

Connectors are essential for RF systems as they have the simple but important task of transferring signals between locations with little to no change. However, even with high-quality RF cables between the antenna connectors and the antenna engineers, there is often a 0.2 dB loss per connector.

There are many connectors available for RF applications. The parameters that determine which type of connector is best for a given application include frequency range, impedance, and physical size. Power handling, cost, and power handling are also important. Long-established connector types like the BNC and SO-239/PL-259 have been replaced by connectors tuned to the priority characteristics for the latest wireless mass-market designs. They are smaller, more efficient, and provide excellent performance at 1GHz+. They are still used in test equipment, rack, chassis, and legacy products.

 

Fundamental specifications used to assess an RF connector include:

Impedance: Most RF cables and connectors are designed for 50-ohm impedance. The 75 O system, commonly used for cable TV installations, is the only exception. The characteristic impedance of RF coaxial cable connectors must match that of the cable. If this is not done, discontinuities can occur, resulting in losses.

VSWR (Voltage Standing wave Ratio): Ideally, there should be unity. Good designs and implementations can keep VSWR under 1.2 across the range of interest.

Frequency range: Most RF work takes place in the 1-to-10GHz frequency range. Consequently, the connector must have a low loss. There are newer connectors available for situations above 10GHz. However, one of the drawbacks is that those connectors are costly, as are the cables.

Insertion Loss (or loss): This refers to the connector loss within the frequency range of the interest. The loss is typically between 0.01 and 0.3 dB. Due to the importance of every watt (or fractional) watt in most designs, even small losses must be minimized and included in the link loss budget. It is particularly important in low-noise frontends where both signal strength (and SNR) are low.

Mating Cycles – How many connect/disconnect cycles is the connector capable of enduring and still meet its specifications? This is usually between 500 and 1000 cycles. The vendor-specified tightening torque on threaded connectors is crucial for maintaining performance and reliability.

Power Handling: The two main factors determining power handling are resistive loss (heating) and dielectric breakdown. Even though designs from decades ago were able to handle tens of megawatts or more, today’s designers focus on low-power devices like handsets, picocells, femtocells, and video interfaces. These connectors are sub-1W, so they can be smaller and have lower power ratings.

 

If you would like to receive a quote for any of custom cables or connectors, please do not hesitate to contact us by sending an email to [email protected] or calling in the USA this phone number (682-325-1944).

 

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