[G0HZU_JMR]

Make sure to be careful if you use it with your Rigol spectrum analyser. I wouldn't advise using it as a coupler to sniff at a (say) 4W radio because the power coupled into the analyser would be 36dBm - 15dB = +21dBm for a 6:1 coupler. 21dBm could be enough to damage your analyser. If the coupler develops an isolation fault then it could be even worse than this.

For coupling transmitters into an analyser I'd advise putting another large attenuator after the coupled port. Also, the coupler looks a bit small. It might only be OK up to 1 watt of power anyway. I used a larger ferrite for my CB/ham coupler and it was OK to about 25W PEP.

A 10:1 (20dB) version could be used with your Rigol analyser with its tracking generator to measure return loss over quite a wide bandwidth. However, I think a homebrew return loss bridge would work a lot better with your Rigol in terms of the directivity and bandwidth the return loss bridge would offer. But a tiny 15dB or 20dB coupler like the one in your image can be a useful tool to have on the workbench.