The Venerable N-Type Coaxial Connector

Peter McNeil | Jul 10, 2024 | RF Connectors

Key Takeaways

TNC (Threaded Neill–Concelman) connectors are threaded RF coaxial interconnects designed for secure coupling, improved performance, and higher frequency capability compared to bayonet-style BNC connectors.

The threaded interface reduces vibration-induced loosening and provides better impedance consistency, making TNC ideal for demanding RF environments.

TNC connectors typically support 50 Ω impedance and reliable operation into the low-GHz range, depending on the specific series and design.

Common applications include mobile communications, wireless infrastructure, test & measurement equipment, rugged RF systems, and military/industrial deployments.

When choosing a TNC connector, evaluate frequency rating, power handling, connector style (straight/right-angle), and environmental robustness based on your RF system’s requirements.

What Is a TNC RF Connector and How It Works

A TNC (Threaded Neill–Concelman) connector is a threaded version of the standard BNC connector, designed to deliver better performance at higher frequencies. Instead of the bayonet-style lock used on BNC, the TNC uses a secure screw-on coupling mechanism, which creates a more stable connection and reduces signal leakage especially in environments with vibration or movement. Inside, the connector uses a standard 50-ohm impedance and supports frequencies typically up to 11 GHz or higher, depending on the specific design. Because of the threaded mechanism, TNC connectors maintain consistent electrical contact and lower VSWR across wider bandwidths, making them reliable for precision RF systems.

Typical Use Cases for TNC RF Connectors

TNC connectors are commonly found in RF applications where both stability and higher frequency performance are important. They are frequently used in wireless infrastructure, Wi-Fi antennas, GPS equipment, test and measurement setups, and portable radio systems. Their rugged threaded design also makes them suitable for harsh environments, including military communications equipment, outdoor RF sensors, and industrial IoT devices. Whenever a standard BNC suffers from vibration, weather exposure, or frequency limitations, the TNC connector becomes the more dependable choice.

Performance Considerations: Frequency, VSWR & Power Handling

When selecting or evaluating a TNC connector, key performance factors include its maximum usable frequency, VSWR performance, and power-handling capability. Most 50-ohm TNC connectors operate reliably up to around 11 GHz, though precision or extended-band versions can go higher. A low VSWR ensures minimal signal reflection, which is especially important for sensitive microwave systems. Power handling depends on frequency and connector quality; at lower frequencies, TNC connectors can handle moderate power levels, but the rating decreases as frequency increases due to dielectric heating. Choosing a well-manufactured TNC connector ensures consistent RF performance, especially in demanding or mission-critical applications.

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.

Frequently Asked Questions (FAQ)

Q1: What does TNC stand for?
A: TNC stands for Threaded Neill–Concelman, named after its inventors and characterized by a threaded coupling mechanism that provides enhanced mechanical stability compared to bayonet connectors like BNC.

Q2: How is a TNC connector different from a BNC connector?
A: Unlike the quick-release bayonet lock used in BNC connectors, TNC connectors use a threaded coupling that improves vibration resistance and impedance stability, especially useful at higher frequencies or in rugged applications.

Q3: What impedance do TNC connectors support?
A: Standard TNC connectors are typically 50 ohms, making them suitable for most RF and microwave systems. Some precision or specialty variants support 75-ohm systems as well.

Q4: What frequency range can TNC connectors handle?
A: Most TNC connectors perform reliably into the 1–11 GHz range, depending on quality and design. Precision 50 Ω TNC variants can maintain low VSWR well into the low-GHz bands.

Peter McNeil | Oct 16, 2024 | RF Connectors

Key Takeaways

SMA connectors are widely used but have frequency limitations, typically up to 18 GHz, with precision variants extending to ~26.5 GHz.

Power handling decreases significantly at higher frequencies due to dielectric heating and small contact size.

SMA connectors are susceptible to wear and damage from repeated mating cycles and improper torque.

At millimeter-wave frequencies, SMA connectors show higher insertion loss and degraded VSWR.

For applications above, 26 GHz, 3.5 mm, 2.92 mm, or 2.4 mm connectors offer superior performance.

What Is an SMA Coaxial Connector?

An SMA (Subminiature version A) coaxial connector is a precision RF connector designed for use in microwave systems requiring stable electrical performance in a compact form factor. SMA connectors use a threaded coupling mechanism to provide a secure connection and are typically manufactured with a 50-ohm impedance. They are commonly used in test equipment, antennas, RF cable assemblies, and wireless communication systems. While standard SMA connectors are generally rated up to 18 GHz, precision variants can extend performance to higher frequencies under controlled conditions.

Frequency Limitations of SMA Connectors

One of the primary limitations of SMA connectors is their restricted usable frequency range. Standard SMA connectors are typically specified for operation up to 18 GHz, beyond which insertion loss, return loss, and signal reflections increase significantly. At higher frequencies, small variations in connector geometry, dielectric material inconsistencies, and manufacturing tolerances can degrade signal integrity. Even precision SMA connectors rated up to 26.5 GHz may struggle to maintain consistent performance in demanding environments, making them less suitable for millimeter-wave, 5G, and high-speed radar applications.

Power Handling Constraints of SMA Coaxial Connectors

SMA coaxial connectors also face inherent power handling limitations due to their small size and narrow center conductor. As frequency increases, the ability of the connector to dissipate heat decreases, leading to higher risks of dielectric breakdown and thermal damage. High RF power levels can cause localized heating, which may degrade connector materials and reduce long-term reliability. These constraints make SMA connectors less ideal for high-power RF applications, especially at microwave and millimeter-wave frequencies where power density is significantly higher.

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.

Recommendations

Use precision SMA connectors only when operating close to the upper frequency limit.

Always apply manufacturer-specified torque values using calibrated torque wrenches.

For high-power RF systems, verify thermal ratings at operating frequency, not just peak power.

Transition to 2.92 mm (K), 2.4 mm, or 1.85 mm connectors for mmWave and 5G applications.

Minimize connector wear by limiting unnecessary mating cycles in test environments.

Signing Out

The Venerable N-Type Coaxial Connector

Related articles

ABOUT US

CONTACT INFO

RESOURCES

POLICIES

Connect with us