LoRa antenna
Description of tuning potted LoRa antenna on lion tracker
Schematic on bottom picture shows how is antenna wired with Murata IC and digital tunable capacitor PE64102 (DTC). DTC is wired in parallel with C7 to add capacitance and with that lower the antenna resonating frequency.
With recommended component values from datasheet we have antenna frequency that is far below 868MHz.
Frequency response with component values from datasheet shows frequency center at 785MHz which is 83MHz to low.
After tuning with capacitor on antenna band select pin we managed to get right frequency curve. Below on picture you can see frequency curve with different capacitor values with the most suitable 3pF capacitor.
Because the capacity is so small we can't fully use the potential of DTC. DTC has 32 possible combinations of capacity and we are operating at the beginning of this scale (at decimal number 4 witch is 2,98pF.
Can we make efficiency of antenna better when potted?
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