Unfortunately, my English is not very good. I still try to explain.
The Ikea Repeater has only one antenna. You get a pigtail like this one.
The pigtail has a conductor and ground. The conductor is soldered to the antenna and ground to any point. If you want, you can now interrupt the original antenna. You can connect everything else to the pigtail. if you work with a booster please consider that this service is not allowed in many countries. It is important to use antennas or boosters with the correct frequency. Please do not use amplifiers with more than 1 watt power. You don’t want to supply your entire city.
Zigbee 2.4 GHz
Zwave 868.42 MHz.
This also works with the Hue Bridge:
