When it comes to microwave circuits, we have to mention coaxial connectors. No matter what frequency band your circuit is in, as long as it needs to be measured on the spectrometer, network analyzer and other instruments, you need to use coaxial connectors. There are many kinds of coaxial connectors: SMA, SMB, SMC, apc-7, K connector and so on. No matter what kind of connector you use, you should pay attention to its applicable frequency range before use. The frequency range of the connector is limited by the excitation of the first circular waveguide propagation mode in the coaxial structure. Reducing the outer conductor diameter will increase the maximum frequency that can be used; Filling space with insulators will reduce the maximum frequency available and increase system loss. The performance of all connectors is affected by the quality of connector interface. If the diameter of the inner and outer conductors deviates from the size required by the design, the plating quality is poor, or the gap at the connection is large, the reflection coefficient and resistive loss of the interface will be degraded. This is why the same connector with good quality can be used at higher frequencies and smaller standing wave coefficient. Of course, if your circuit frequency is relatively low, Original: knowledge about microwave and millimeter wave coaxial connectors, or just a test version, under the condition of low requirements, You buy a few dozen of them directly in Town God's Temple, that's what they call it.

The following is a brief introduction to several connectors commonly used in measurement and test applications.

Apc-7 (7mm) connector

Among all 18GHz connectors, apc-7 (Amphenol precision connector - 7 mm) has the lowest reflection coefficient and can provide the best repeatability measurement. This connector was jointly developed by HP and Amphenol in the 1960s. This is a non-polar connector designed for the most demanding applications, especially for metering and calibration applications.

N-type connector

The n-type (U.S. Navy) 50 Ω connector was designed for military systems below 4GHz in the 1940s. Improvements in the 1960s pushed the performance to 12GHz and later to 18GHz. Some 75 Ω products use an n-type design with a smaller center conductor diameter, but are not compatible with 50 Ω connectors.

SMA connector

I believe this is the most commonly contacted connector. As long as you are making circuits, you will basically have used it (unless you are making millimeter wave circuits, you may not have used the original: knowledge about microwave millimeter wave coaxial connectors). The SMA (micro a) connector designed by Bendix scintilla is one of the most commonly used connectors for RF / microwave. It adopts semi-rigid cable and is suitable for infrequent connection. Due to the difficulty of fixing the dielectric pillar, the reflection coefficient of most SMA connectors is higher than that of other connectors at 24 GHz.

3.5 mm connector

The 3.5 mm connector was mainly developed by HP, now Agilent, and manufactured by Amphenol in the early stage. Its design strategy is to use conventional SMA size to realize highly reliable physical interface, so as to realize thousands of repeated connections and reach 34GHz.

1.0 mm feedthrough

One end of the feed through adapter is a 1.0mm female connector, and the other end is a glass to metal sealing interface. It is suitable for ultra-high frequency (up to 110 GHz) signal jump from coaxial to microstrip line package or circuit board.

2.92 mm connector

That is, the K connector we usually use. In 1983, William of wiltron company Old. Field senior engineers developed a new type of K-type connector on the basis of summarizing and overcoming the previously launched millimeter wave connector. It can be used in the dc-46ghz frequency band, has good electrical performance, and is compatible with the widely used SMA connector. It is quickly recognized by the majority of manufacturers, and has become one of the most widely used millimeter wave connectors in the world. 2.92mm connector can adapt to SMA and 3.5mm connector. When used in 46ghz band, it has excellent performance and is cheaper than 3.5mm connector; When used below 18GHz, the performance is better than SMA joint. Therefore, when you see that the appearance of K connector and SMA connector is not much different, but the price is dozens of times more expensive, don't be surprised. It's a high-grade product.

2.4 mm connector

The 2.4 mm connector is a 50 GHz connector jointly developed by HP, Amphenol and M / A-COM. This design solves the vulnerability of SMA and 2.92 mm connectors by increasing the outer wall thickness and strengthening the slots. It can accurately adapt to SMA, 3.5mm and 2.92 mm connectors. However, since there are not as many manufacturers producing 2.4mm connectors as K-type connectors and the price is high, it is not widely used as K-type connectors.

1.85 mm connector

1.85 mm connector is a connector developed by HP company in the mid-1980s, which is now Agilent company. Its working frequency reaches 65ghz. In 1988, HP provided this design to the public to promote the standardization of connector types; Through development, several manufacturers can provide several such devices. The 1.85mm connector fits with the 2.4mm connector and has the same robustness. In recent years, the 1.85mm connector has been optimized to reach 67 GHz frequency. Many experts believe that this connector is the smallest coaxial connector possible for general use at 67 GHz.

1.0 mm connector

The 1.0 mm connector is designed to support all transmission modes up to 110 GHz, which is an important achievement of precision manufacturing industry that can realize reliable and flexible interconnection.

To sum up briefly: if the circuit you need to measure and test is below 18GHz, you can choose SMA connector, n-type connector and apc-7 connector. The specific choice is based on your circuit type and cost. If your boss has too much money to spend, you can also use K-type connector and other original: knowledge about microwave and millimeter wave coaxial connectors. If you measure and test in the millimeter wave band, you can choose K-type connector or 2.4mm connector. Why not choose a 3.5mm connector? Because compared with K-type connector, it has neither price advantage nor performance advantage (applicable frequency is not as high as K-type connector).