I want to use one shared antenna for the Lora/FSK transceiver sx1272 and LTE/GSM SIM700E module, with BGS12SN6 as a switch.

I've matched the antenna with two conductor and validated the result with a VNA after the switch (sx1272/SIM7000E->Switch->TestPoint->Matching->Antenna) with a reasonable performance (-28.9db 50.5+j0.17 @868MHz).

I strictly copied the switchless reference design from Semtech, but for some reason I get really a bad performance, even if I use an external 30db perfectly matched 50ohm antenna. I've already used the antenna for an other board with a Si4463 and get way better results (testing with wireless M-Bus devices, the Si4463 gets about 800 devices in the areas, the Sx1272 only about 150)

So I got curious and tried to rebuild the reference design with qucs (see image below (red line antenna without filter, blue line with reference design filter), but i don't think the result can be right.

The PCB schematic looks like the image below, the VNA was connected to J5, with C9 placed and C30 left open.

Is there anything I missed or did a big mistake? I'm grateful for any hint or idea.

Just in case I'm adding the application flow:

• the reference design is really bad and I rebuild the design with qucs and was a little shocked are meaningless statements. They impart no technical value at all to help you with this: Did I do something wrong?. Then you say this: I can't change the matching network because otherwise the GSM module would perform bad but I'm unclear where it fits into things schematically. Mar 8 at 12:46
• Sorry for the misunderstanding. I wanted to know if i did something wrong in qucs and get wrong results. I can't change the matching network because otherwise the GSM module would perform bad but i could change the values in the reference design, but i don't know what the sideeffects this would have.
– Wowa
Mar 8 at 13:06