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Microwave connectors

Click here to go to our VSWR page

Updated January 19, 2009

Chess-set photo courtesy of TVB of leapsecond.com!

New for January 2009: we have a new page on a proposed color-code for connectors!

New for March 2008: we have a new pages on SMB, SMC, SMP and SMPM connectors!

Attention microwave connector vendors: this page or its subpages can be sponsored for small change every month. This page (and its associated sub-pages) is full of useful info on microwave connectors, and there's infinite room for more useful information (hint, hint).

Attention companies that use microwave connectors: we recommend that you use our section on connector care as a mandatory reading assignment before any of your new hires are even allowed in your laboratory! Check out our connector care poster in our download area!

Here is a clickable index to help you navigate through our material on connectors:

Microwave connector overview

Connector sex (separate page)

Connector species and their frequency limitations

Type N connectors

SMA and SSMA connectors (separate page)

SMC connectors (separate page)

Precision connectors (separate page)

7 mm connectors

3.5 and 2.9 mm connectors

2.4 and 1.85 mm connectors

1 mm connectors

How (not) to trash a cal kit (separate page)

Push-on connectors (separate page)

Blind mate connectors

SMB connectors (separate page)

SMP connectors (separate page)

SMPM connectors (separate page)

Adapters

Connector care - mandatory reading! (separate page)

Storing connectors

Connector torque (separate page)

How to deal with stuck connectors

Gauging connectors

Cleaning connectors

Connector vendors

Possible future topics

Microwave connector overview

Microwave connectors are now a two billion-dollar-per-year industry. There are a wide variety of microwave connector families and more choices are added each year. Microwave connectors are used to make low VSWR coaxial connections, and can be used as the terminations ("ends") of coaxial cables, installed into housings, and increasingly onto circuit cards.

Most microwave systems use 50 ohm characteristic impedance but some use 75 ohms (BEWARE! type some connectors such as type N come in both 50 ohms and 75 ohms. Don't mix these up!) All connectors described on this page are 50 ohms unless noted. For the equation for the characteristic impedance of coax, see coaxial transmission lines, or go straight to the coax calculator.

Elbow connectors

The term "elbow" is another bit of connector slang, it means a right-angle bend connector or adapter. Right-angle connectors come in two types: 90 degree, and swept (see photo below). In general, the swept connectors are better at high frequencies, and the outer jackets are molded rather than machined. If you took apart a 90 degree elbow you'd see why. It's because the dielectric typically is not continuous at the 90 degree junction, so there is some parasitic inductance that screws up the VSWR.

One property of any coax transmission line is that it has a cutoff frequency above which the desired TEM mode will no longer propagate (see transmission lines for a discussion of cutoff frequency, or go straight to the coax calculator). The maximum frequency of operation of coax connector families cannot exceed this limitation. The industry-accepted frequency limits of connectors families are generally 95% of their theoretical cutoff frequency.

The following table lists all of the major connector families. Generally, cost increases proportionately with frequency limit. And "air" costs a lot more than "PTFE", which may seem counterintuitive, until you see how the center conductor has to be supported in an air-dielectric connector. Some connector history is included in the right-hand column.

Connector type

Frequency Limit

Dielectric

Comments and history

BNC

4 GHz

PTFE

"Bayonet type-N connector", or "Bayonet Neill-Concelman" according to Johnson Components. Developed in the early 1950s at Bell Labs. Could also stand for "baby N connector".

SMB

4 GHz

PTFE

"Sub-miniature type B", a snap-on subminiature connector, available in 50 and 75 ohms.

OSMT

6 GHz

PTFE

A surface mount connector

OSX, MCX, PCX

6 GHz

PTFE

MCX was the original name of the Snap-On"micro-coax" connector species. Available in 50 and 75 ohms.

MMCX

PTFE

Micro-miniature coax connector, popular in the wire industry because its small size and cheap price.

SMC

10 GHz

PTFE

Sub-miniature type C, a threaded subminiature connector, not widely used.

SMA

25 GHz

PTFE

Sub-miniature type A developed in the 1960s, perhaps the most widely-used microwave connector system in the universe.

TNC

15 GHz

PTFE

"Threaded Neill-Concelman" connector, according to Johnson Components, it is actually a threaded BNC connector, to reduce vibration problems. Carl Concelman was an engineer at Amphenol.

N

11 GHz
normal

18 GHz
precision

PTFE

Named for Paul Neill of Bell Labs in the 1940s, available in 50 and 75 ohms. Cheap and rugged, it is still widely in use. Originally was usable up to one GHz, but over the years this species has been extended to 18 GHz, including work by Julius Botka at Hewlett Packard.

APC-7, 7 mm

18 GHz

PTFE

APC-7 stands for "Amphenol precision connector", 7mm. Developed in the swinging 60s, ironically a truly sexless connector, which provides the lowest VSWR of any connector up to 18 GHz.

OSP

22 GHz

PTFE

OSP stands for "Omni-Spectra push-on", a blind-mate connector with zero detent. Often used in equipment racks.

3.5 mm

26.5 GHz

Air

A precision (expensive) connector, it mates to cheaper SMA connectors.

OSSP

28 GHz

PTFE

OSP stands for "Omni-Spectra subminiature push-on", a smaller version of OSP connector.

SSMA

38 GHz

PTFE

Smaller than an SMA.

2.92 mm

40 GHz

Air

Precision connector, developed by Mario Maury in 1974. 2.92 mm will thread to cheaper SMA and 3.5 mm connectors. Often called "2.9 mm".

K

40 GHz

Air

The original mass-marketed 2.92 mm connector, made by Wiltron (now Anritsu). Named the "K" connector, meaning it covers all of the K frequency bands.

GPO, OSMP, SMP

40 GHz

PTFE

"Gilbert push-on", "Omni-spectra microminiature push-on"

OS-50P

40 GHz

Smaller version of OSP blind-mate connector.

2.4 mm

50 GHz

Air

2.4 mm, and 1.85 mm will mate with each other without damage. Developed by Julius Botka and Paul Watson in 1986, along with the 1.85 mm connector.

1.85 mm | 60 GHz | Air | Mechanically compatible with 2.4 mm connectors.
V | 60 GHz | Air | Anritsu's term for 1.85 mm connectors because they span the V frequency band.
1 mm | 110 GHz | Air | The Rolls Royce of connectors. This connector species works up to 110 GHz. It costs a fortune! Developed at Hewlett Packard (now Agilent) by Paul Watson in 1989.

Here's another way to look at connector frequency limits:

Type N connectors

These are cheap and rugged, for these reasons you will find them all over your laboratory.

Adapters

Within any connector family there are three adapters you can use. A male-to-male adapter refers to an adapter with two male ends. This is often referred to as a "barrel" adapter. A female-to-female adapter has two female ends; it is often referred to as a "bullet" adapter. An adapter with one male end and one female end is often referred to as a "connector saver". This is because this type of adapter is often screwed onto an expensive piece of test equipment or component that requires a lot of connect/disconnect cycles. If an incident occurs where one of the connectors is damaged, it is far cheaper to throw away and replace the connector saver than to repair expensive equipment that it is protecting. Below is a picture of an SMA connector saver, barrel and bullet adapter.

Between species adapters are a huge part of the RF connector industry. For sake of argument, if we accept that there are 10 different connector species (and there are a whole lot more than 10), and each has two sexes, there are 20+19+18+17+16+... different permutations, which adds up to 210 total! This is why connector catalogs are so thick. Of course, there are some permutations that would have a limited market, so they are deleted from the lineup. For example, no one is going to buy a 1 mm to type BNC adapter.

Connector vendors

Alas, some good things must come to an end. The days when we posted free links to connector vendors that we prefer are over!

If any connector vendor wants a sweet business deal, show us some green, and we'll link this page to your web site. Check it out, this page gets over 50 hits per day, what does yours get? Contact us!

Possible future topics

Bulkhead or flange-mount connectors

Feedthrough connectors

Hermetic connectors

Crimped versus soldered connectors for cables

Captured versus floating center contact

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