What factors should be considered when selecting RF connectors

作者： 沃锌科技 时间：2023-11-28 15:58:42 阅读：13

RF connector is a connecting device in RF transmission systems that can transmit RF signals with low loss and reflection, and provide fast and repeated connections. Mainly composed of contacts, insulators, shells, and accessories< Span Microsoft="" yahei ";=" "font size:=" "18px;"="" font size: 18px; "; "Style=" box sizing: border box; Padding: 0px- Webkit tap highlight color: rgba (0, 0, 0, 0) ">VSWR (Voltage Standing Wave Ratio) It is a measurement standard for measuring the amount of signal returned from a connector. It is a vector unit that includes amplitude and phase components. It is very important to recognize this, especially when considering the composite effects of multiple connectors on transmission lines. Impedance mismatch can cause reflection, and if the cable used has a 50 ohm impedance, the connector must also maintain a 50 ohm impedance. The size change from the cable to the connector transmission line, the insulation medium cascading inside the connector, and the contact loss of the conductor are the main factors leading to mismatch. There are usually two methods to determine the VSWR of a connector. The first method is to use the "flat line limiting" method throughout the entire frequency band. For example, for straight BNC plugs with flexible cables, the VSWR is specified as a maximum value of 1.3:1 up to 4 GHz (usually written as a maximum of 1.3). The second method is to consider that VSWR is a typical frequency direct function in practical situations, and to connect a straight SMA plug with RG-142 B/U cable, VSWR can be described as: VSWR=1.15+0.01 * F (GHz) to a maximum frequency of 12.4 GHz. For example, at 2 GHz, the maximum allowable VSWR would be 1.15+2 *. 01 or a maximum of 1.17. At 12.4 GHz, it will be 1.15+12.4 *. 01 or a maximum of 1.274. Naturally, these values can be converted into return loss or reflection coefficient.

Insertion loss and its determination

insertion loss  ρ， Defined as:

ρ= 10 * log (Po/Pi), in dB

Po - Power output

Pi - Power input

There are three main reasons for insertion loss:

1. Reflection loss, dielectric loss, and conductor loss. Reflection loss refers to the loss of connectors caused by standing waves. Dielectric loss refers to the loss of energy propagation in dielectric materials (such as Teflon, rexolite, delrin, etc.). Conductor loss refers to the loss caused by the conduction of energy on the surface of a connector conductor, which is related to material selection and the use of electroplating. Usually, connector insertion loss ranges from several hundredths of a dB to several tenths of a dB. Similar to the method of specifying VSWR, it can be specified as a "flat line constraint" or as a function of frequency. As with the example of VSWR, for straight BNC plugs with flexible cables, BNC can be specified to a maximum of 0.2 dB under maximum 3 Ghz test conditions.

2. For SMA, insertion loss can be specified under 6 GHz testing conditions ρ= 0.06 * (f - GHz) dB. For example, at 4 GHz, the maximum insertion loss is 0.06 * 2 or 0.12 dB. Although connectors can be used over a wide frequency range, they are typically only tested at specified frequencies, as precise measurement of very small losses is a precise and time-consuming process. This testing process is defined in MIL PRF-39012.