Benefits of SMA Quick Connect Adapters

by Peter McNeil | Jul 06, 2023

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SMA Quick Connect Adapter

SMA Coaxial connectors are one of the most common coaxial connector types used in almost every application coaxial connectors are used. SMA connectors can be made to a precision grade which extends the frequency range of operation to 18 GHz, or even 26.5 GHz. Hence, SMA connectors can cover frequency bands from HF, VHF, UHF, L, S, C, X, Ku, and K. Given the ubiquity of SMA coaxial connectors in test and measurement, automated test equipment (ATE), handheld/portable RF/microwave equipment, etc., there are often situations where it is necessary to repeatedly connect/disconnect SMA connectors. As opposed to wearing out the ports of critical equipment, adapters are often used at the ports of equipment and on specialized coaxial cable assembly connections. A step up from a standard coaxial adapter is a quick-connect coaxial adapter, such as an SMA Quick-connect Coaxial Adapter.

Where a typical adapter presents low VSWR, insertion loss, and allows for interconnect between two coaxial connections while minimizing wear and tear, a quick-connect provides all of these benefits as well as rapid connect/disconnect capability. The quick-connect eliminates the requirement to fully thread the SMA connector onto the interface and properly torque the SMA connector to specified torque. SMA quick-connect adapters are typically push-turn thread on, somewhat similar to bayonet style connectors, but also only require a simple pull-off instead of unthreading. No tooling is needed to ensure a quality connection with SMA quick-connect adapters, which saves the need to have a torque wrench accessible to ensure repeatable connections. These quick-connect adapters offer the same precision performance as typical SMA adapters with the added convenience of quick-connect features.

This type of quick-connect adapter is ideal for use in test and measurement equipment, be it in the laboratory or with field use of portable test equipment, where there may be repeated cycling. An example application is where a field technician may need to have several adapters available to mate with various coaxial connector types connected to different equipment and ports. Using SMA quick-connect adapters with portable test equipment could allow for rapid changing of the adapters without the need to constantly thread and un-thread coaxial adapters. Another example would be during prototyping or engineer volume testing of PCB interconnects where it may be necessary to connect/disconnect from several ports over the length of a full diagnostic or quality control check.

As RF circuits and electronics became more prevalent in military and defense applications in the 1950s, there have been a variety of RF connector types that were developed to solve the challenges for specific applications. One of these connectors that became referenced in MIL-STD-348 was invented by Paul Neill and Carl Concelman, the Threaded Neill-Concelman or TNC RF Connectors. The TNC connector was developed by the same pair that developed the BNC connector and is essentially a threaded BNC connector.

The threaded connector of the TNC enables superior RF performance over the bayonet type connector of the BNC. While BNC connectors are typically only specified to 2 GHz, TNC connectors are often specified to 11 GHz. Like BNC connectors, TNC connectors can be found in 50-Ohm, 75-Ohm, and reverse polarity variants. The TNC connector uses a 7/16 in by 28 thread (7/16”-28). This should not be confused with a DIN 7/16 (7/16 DIN) connector which is designated based on the diameter of the mating services in millimeters.

Given the legacy of BNC and TNC connectors, these connectors are still widely used for applications below 10 GHz. There are extended frequency range designs, or high precision designs, of these connectors that push the upper frequency range to 18 GHz, similar to precision SMA connectors. These connectors are found in aerospace applications, avionics equipment, radar, and terrestrial communications such as cellular base stations and antenna connectors. The TNC standard, and TNC Female RF Connectors For Terminals, are designed to be ruggedized coaxial connectors, which is why these connectors are often used in harsh environment applications.

Moreover, TNC connectors have wide compatibility with many common RG coaxial cable types and many others. The exact compatibility depends on the type of attachment methods used with the TNC connector, of which there are several varieties including crimp, solder, and push connectors. As with many other coaxial connector standards, it is common to use male coaxial connectors in cable assemblies and female coaxial connectors as bulkhead, terminal, or panel mount connectors. This isn’t a standardized rule, merely common practice. For instance, it is more common to see TNC Male Connectors For Coax and female terminal connectors than vice versa.

Some manufacturers use female contacts inserted into plugs and male contacts inserted into jacks to ensure incompatibility between reverse polarity and standard polarity TNC connectors. Other manufacturers may instead use reverse threading on the plugs and jacks to ensure incompatibility between the two types.

Peter McNeil | Jul 20, 2023 | Antennas RF Connectors Waveguides Coax Cables

Radio Frequency (RF) signals are merely any useful electromagnetic radiation within a portion of the spectrum that is compatible with available technology. These can be RF signals used for communication, sensing, or any other purpose, such as RF heating, RF plasma, or even RF propulsion. RF signals can be conducted through open-air channels, space, through fluids, through the ground, along/within conductors, or through dielectric channels. So, what is an RF connection? An RF connection is simply the point at which two RF paths meet. This could be via RF Coaxial Connectors, Waveguides, RF Antennas, or any other medium that RF signals pass through. Typically, an RF connection implies some form of hardware connection between two RF paths, such as a coaxial connector, waveguide, RF antenna, PCB vias, probe interfaces, etc.

In the case of an RF antenna, the antenna itself is a connection between the air-interface and the conductive interface, such as a coaxial transmission line, waveguide, or planar transmission line/waveguide. Hence, for a wireless link a signal is injected at an antenna’s RF port, the RF signal passes through two RF conductive ports and two air-interfaces. Hence, there are four RF connections in that simple path between two antennas and their RF ports. This isn’t counting the connection between the antenna’s RF ports and any type of transmission line or other conductive RF path.

RF Coaxial Cable Assemblies are considered a single RF connection, however, there are actually two RF connections within a coaxial cable assembly. Where the coaxial cable and RF connector meet there is a connection, as well as the connections between each of the RF connectors and the ports that they are connected to. Hence, even for a simple cable assembly connection there are four RF connections. If an RF coaxial cable assembly is the interconnect between an antenna and another RF path, such as a transceiver, then the wireless link between two antennas with RF coaxial cable assemblies involves six RF connections on each side of the wireless link, or 12 RF connections total.

It is important to be cognizant of every RF connection within a path, as that connection is an opportunity for failure, signal degradation, or signal leakage. RF signal paths tend to be very susceptible to degradation from poor RF connections. For instance, an improperly attached coaxial connector can lead to an impedance other than the characteristic impedance of the transmission line and/or become weak and lead to a disconnection failure. In general, there is never a perfect impedance match at a given RF connection, so there is always some loss, reflection, and a voltage standing wave ratio greater than 1:1.

Benefits of SMA Quick Connect Adapters

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