When use RF cables for testing, the RF cable stability is generally required in the following situations:
1. When testing with RF cable assemblies, we hope that the amplitude and phase are stable, so that the test indicators will be accurate. Similar to weighing the product with an electronic scale in the market, the electronic scale is stable and the value weighed is accurate.
2. When used in the system, some systems have higher requirements on the phase amplitude. The phase and amplitude fluctuation of the cable assemblies will affect the stability of the whole system, so it is also necessary to stabilize the phase.
The change in amplitude is the fluctuation of the insertion loss. The insertion loss should be as small as possible. The change of phase can be simply understood as the change of length. When the cable is bent or the temperature changes, the length of the cable will change slightly. This change affects the phase. The principle is as follows:
When the cable length of L1 changes to L2 and the length changes by ΔL, the phase changes by Δφ.
Objectively speaking, the amplitude and phase of the cable assembly cannot be avoided. Only some cable manufacturing processes can be improved to make the amplitude and phase change smaller. This is stable amplitude and phase cable.
There are two conditions that affect the cable amplitude and phase:
1. Temperature: When the temperature changes, the principle of thermal expansion and contraction will inevitably lead to changes in cable size. The temperature change generally happens in outside, so the cable assembly will be required for temperature amplitude and phase stability when used as an outdoor system connection, such as a cable connected to an outdoor antenna. After the cable is assembled, it is basically fixed, so it is generally not required for the mechanical stability.
2. Mechanical: When the RF cable assembly is used as a test cable, it is generally used in a constant temperature and humidity room, the temperature effect can be ignored. However, when testing the product, it is necessary to bend the cable continuously to make the mechanical size change, so the test cable generally requires the mechanical amplitude and phase stability.