N-Type Coaxial Connectors in A Nutshell

by Peter McNeil | Jan 18, 2024

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Type-N Coax Connector

N-type Coaxial Connectors are one of the most common coaxial connector types used in wireless communication and sensing systems. This connector type has been around since the 1940s and was originally designed for military applications not exceeding 1 GHz maximum operating frequency. These coaxial connectors can be found in virtually all applications that operate below 6 GHz, though there are such connector variations that go as high as 11 GHz or even 18 GHz. N-type coaxial connectors are typically threaded connector types, though there are several variations, as there are with another common coaxial connector type, the SMA connector. N connectors were originally defined in MIL-STD-348 and come in both 50 Ohm and 75 Ohm versions. This is sometimes an issue as many manufactured versions of these connectors are not labeled as either 50 Ohm or 75 Ohm, and may be confused in broadcast, military, automotive, and other applications that may use both 50 Ohm and 75 Ohm N-type connectors, which are not typically compatible.

Like other coaxial connectors, there are female and a male N-type coaxial connectors, though there are hermaphroditic connector variations also available. These are less common than the typical threaded type, as hermaphroditic connectors tend to be expensive and are generally only used for test and measurement applications.

N-type coaxial connectors typically can handle more power than SMA coaxial connectors, as these connectors are larger and allow for wider spaces between the conductors. However, the extent of N-type connector power handling depends on the dielectric breakdown, connector design, connector material, and frequency of operation. Like other coaxial connectors, the power handling is a function of frequency and decreases at higher frequencies.

The 50 Ohm N-type connector is one of the most common connectors for test and measurement equipment and metrology applications for frequencies within range of precision variations of this connector (~11 GHz). Hence, there are many devices and components that operate to 6 GHz, and even X-band, that use these connectors as an interconnect interface. There are N-type connectors with attachments for bulkheads, coaxial cables, surface mount soldering (reflow), thru hole soldering, end launch, and even reusable end launch N-type connectors. There are also highly specialized versions of these connectors, such as high voltage (HV), reverse-polarity, left-hand thread, and others. Given the popularity of N-type connectors, there are a wide array of variations and customized adaptations well beyond the scope of this article.

RF Interconnect is another term for RF connections between devices, boards, ports, RF cable assemblies, waveguide, probes, antenna, and etc. As discussed in a previous blog post, What is an RF Connection, RF interconnects are a method of transferring RF signals from one node to another either conductively, through a transmission line (RF coaxial connectors/ coaxial cable assemblies), or through a waveguide. It can be argued that an RF antenna is also a form of interconnect, though it is really a transducer that converts electrical signals carried conductively to a free-space wavefront.

When speaking of RF interconnect, this generally refers to connections between circuit boards, devices, subsystems, systems, and between interconnects. The reason RF interconnects are used, especially transmission lines and waveguides, is because containing the RF signal energy in a transmission line or waveguide is generally a much more efficient method of transferring that signal energy from one point to another, that signal is shielded to some degree from interference/noise injections from outside sources, and these types of connections help to ensure that the signal is harder to intercept, jam, block, or otherwise interfere with.

There are a variety of types of transmission lines and waveguides, as well as other types of RF interconnects. The most common types of RF transmission lines that most engineers and professionals are aware of are coaxial transmission lines. These make up the bulk of RF interconnects between modules, subsystems, and systems. Waveguides such as rectangular, circulatory, and elliptical waveguides are also commonly used for high power, precision, and extremely high frequency signals in the millimeter-wave range. There are other types of transmission lines, including planar transmission lines used on planar substrates/laminates, such as PCB, low-temperature co-fired ceramic (LTCC), high-temperature co-fired ceramic (HTCC), flex-PCBs, semiconductors, and others. Example planar transmission lines are coplanar transmission lines and striplines, of which there are a variety of configurations. There are also planar waveguides, such as a microstrip.

There are also a variety of different connector and adapter styles that should be included in the RF interconnect categories. These include adapters from different transmission line types, such as a planar transmission line to a coaxial transmission line, or between different types of coaxial connector types. There are also adapters between coaxial transmission lines and waveguides. It is important to note here that coaxial transmission lines are broadband RF signal carrying medium, while waveguides are banded based on the geometry and structure. Hence, any adapter between a coaxial transmission line and a waveguide will have a lower cutoff frequency limited by the waveguide and a higher cutoff frequency either limited by the coaxial transmission line or waveguide, whichever is lower.

It can be argued that certain resonant coupling structures can also be considered interconnects, as well as components such as directional couplers and probes. However, passive structures like directional couplers and probes are generally not considered RF interconnects as they lack a conductive path for the signals and rely on coupling to fields external to the conductors of the main RF signal paths.

N-Type Coaxial Connectors in A Nutshell

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