How to choose RF cable components correctly? Basic selection principles for RF cable components

作者： 沃锌科技 时间：2023-11-28 15:56:32 阅读：12

The cost of (-120dB) semi rigid cables is higher than that of semi flexible cables, and they are widely used in various RF and microwave systems.

Flexible braided cable is a type of "test grade" cable. Compared to semi rigid and semi flexible cables, the cost of flexible cables is very expensive because there are more factors to consider in the design of flexible cables. Flexible cables need to be easy to bend multiple times and maintain performance, which is the most basic requirement for testing cables. The contradiction between softness and good electrical performance is also the main reason for the high cost.

Characteristic impedance RF coaxial cables consist of conductors, media, outer conductors, and sheaths. Characteristic impedance is the most commonly mentioned indicator in RF cables, connectors, and RF cable components. The maximum power transmission and minimum signal reflection depend on the characteristic impedance of the cable and the matching of other components in the system. If the impedance is perfectly matched, the loss of the cable is only the attenuation of the transmission line, and there is no reflection loss. The characteristic impedance of a cable is related to the ratio of the size of its inner and outer conductors. Due to the "skin effect" of RF energy transmission, important impedance related dimensions are the outer diameter of the inner conductor and the inner diameter of the outer conductor in the cable:

Ω √ ε The characteristic impedance of most RF cables used in the communication field is Ω; Ω cables are used in broadcasting and television.

(VSWR)/

The magnitude of reflection can be expressed as the voltage standing wave ratio, which is defined as the ratio of incident and reflected voltages. The calculation formula for is as follows:

√√ Where is the reflected power and is the incident power.

The smaller the size, the better the consistency of cable production. The equivalent parameters are reflection coefficient or return loss. The transmission efficiency of a typical microwave cable component, converted to return loss, is the incident power. The meaning of matching efficiency is that if the input power is, when is, the output power is, which is reflected back.

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The average power capacity refers to the ability of a cable to consume thermal energy generated by resistance and dielectric losses. In practical use, the effective power of cables is related to temperature and height:

=When selecting cables, x x x should also consider the above factors.

Vp=(1/) x 100

The phase stability during bending is a measure of the phase change of a cable during bending. Bending during use will affect the insertion phase. Reducing the bending radius or increasing the bending angle will increase the phase change. Similarly, an increase in the number of bends can also lead to an increase in phase change. Increasing the ratio of cable diameter to bending diameter will reduce the phase change. The phase change and frequency are basically linearly related. The phase stability of low-density dielectric cables is significantly better than that of solid dielectric cables, and the phase stability of cables with multiple inner conductors is better than that of cables with single inner conductors.

If two or more signals are simultaneously input into a nonlinear system, new frequency components will be generated at its output due to intermodulation distortion. In modern communication systems, engineers are most concerned about third-order intermodulation products, as these useless frequency components often fall into the receiving frequency band and cause interference to the receiver.

In equipment, try to use semi-rigid or semi-flexible cables instead of flexible cables. Use single stranded inner conductor cables with smooth surfaces and high-quality joints. Use joints with sufficient thickness and uniform coating. Use joints with the largest possible size to ensure good contact between joints. Use joints made of non-magnetic materials