Good morning,
I'm planning to design an antenna for a 868 MHz TI chip. While the AN are useful, our product will have its own particularities, so I would like to have some doubts solved. Hope we can do this together :)
In all the designs from TI Antenna DK, there is the SMA, a wide trace, a matching stage, and an antenna:
1) Why is the clearance around the wide trace so wide? Wouldn't be 50 Ω anymore if instead of a clearance of 4 mm (157 mil) was 1mm (39 mil)?
2) What about if I want to get rid of the SMA and this wide trace. Theoretically, by placing my transceiver output just before the matching stage, everything would be ok. Am I right?
3) My last question is a mix between the previous two. Just imagine I cannot place my 868 MHz transceiver this close to the matching stage. I have to place it 2 cm (about one inch) far away from the antenna. I mean, there is a microstrip from transceiver to antenna and, even if RF traces should be kept as short as possible, it is this long. In addition, in a real design, you cannot devote as much clearance to this microstrip as in the first question, and either cannot be that wide (on FR4 1.6mm, a 50 Ω is effectively about 2mm wide). So, I ask, how has this microstrip to be designed to be thin and this long and still 50 Ω? Does it need one impedance matching stage at the end, close to the antenna, and one at the beginning, at the output of the transceiver?
Ok, just let me know your wisdom and thoughts.
Have a nice day.