I am designing a wearable product that uses GPS. In prototypes up to now we have used a patch antenna, and it worked great, however in this revision to cut down on size, we put in a chip antenna, along with a circuit to do antenna tuning.
When I run the GPS I get very consistent results, but they are quite far away from where I actually am. They tend to be about 0.014 degrees south and 0.139 degrees east of where I am.
I have a feeling that antenna tuning is causing the problem. My circuit schematic and layout is below. I believe that I have followed all of the antenna manufacturers guidelines in regards to layout around the antenna.
I do not have / have access to a network analyzer to help me tune the antenna, so my method of tuning will likely be guess and check. (Update: I can afford the low end Rigol spectrum analyzer)
How do you use a Pi circuit and spectrum analyzer to tune an antenna? What values of parts would I need to try and such?
The antenna I am using is: JTI 1575AT43A0040
The chip I am connecting it to is: SIM868
The keepout square around the antenna is 18.8mm x 10.4mm
I am working with standard US GPS frequency.