There are several factors that will determine the choice of connector series and style. Cable and frequency range are the primary factors. It is good engineering practice to try and match the connector size (diameter) and cable diameter as closely as possible in order to minimize reflections. The larger the difference between cable diameter and connector diameter, the worse the performance will be. Reflections will generally increase as a function of frequency, and smaller connectors will primarily perform well at higher frequencies. For very high frequencies (above 26 Ghz), precision, airline connectors may be needed.
Frequency range will determine the connector series used. Our Frequency Range Chart gives an overview of our various connector series and their standard frequency ranges. In general, it is advisable to use push-on or bayonet style connectors at low frequencies, typically below 6 Ghz. Threaded connectors should be used for high performance, low noise applications.The cable that is specified will generally determine the impedance of the connector used. 50 and 75 ohms are the standard impedances used by most designers, and several connector series come in both 50 ohm and 75 ohm versions. At frequencies below 500 Mhz or so, 50 ohm connectors can be used on 75 ohm cable (and vice versa) with acceptable performance levels. The reason for doing this is that 50 ohm connectors are generally less expensive due to their greater usage. Aside from trying to match the cable and connector as closely as possible in size to minimize reflections, connector interface and dielectric materials are also important considerations.
Line to line and air interfaces such as the SMA and Type N give excellent high frequency, low reflection performance. Overlapping dielectric interfaces such as BNC and SMB are usually limited in performance vs. frequency. The usual figure of merit for a connector’s performance is its Reflection Coefficient. This is a measure of how much signal is reflected back from the connector. It can be expressed in terms of Reflection Coefficient, VSWR (Voltage Standing Wave Ratio) and Return Loss. Power or voltage requirements are also a factor determining the connector to be used in a particular application. High power applications will dictate the use of large diameter connectors such as 7-16 DIN and HN for example. Average power handling is normally limited by the cable’s power specification and is usually determined empirically. The voltage breakdown level of the connector limits peak power. Power handling capability will diminish as a function of frequency and altitude.
