Hello Viral Vasa,
AT1 should start with a 1.8nH inductor and keep the AT2 as a 0 ohm resistor. To ensure the antenna is tuned properly I recommend placing a semi rigid coax on the trace just in front of the SAW filter on the M20057-1 after lifting the component just before the SAW filter to ensure the antenna is still tuned to 1575MHz. Sometimes placing the antenna in your plastic housing will shift the frequency lower and AT1 will need to be adjusted to re-center the frequency.
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