can be divided into positive reflection and negative reflection. When the resistance in the section
from the chipset RF pin to the antenna is larger than 50Ω, positive reflection will be formed and the
power will grow bigger than normal; if the resistance is smaller than 50Ω, negative reflection will be
formed and the power will become smaller than normal. By the way, mismatch of the resistance will
affect the performance of the PA within the chipset, leading to PA’s premature entry into the
saturation regions, thus resulting in large distortion of the signals and according poor EVM
performance.
Solution: leave a π shaped circuit on the RF wiring, which shall allow match of the resistance with the
antenna, so as to enable the resistance in the section from the chipset RF pin to the antenna to
approximate 50Ω.
4. Typical phenomenon: TX performance is not bad, but the RX sensitivity is rather high.
Problem description: Good TX performance means proper RF impedance matching. RX
performance is strongly influenced by the external interference coupling to the antenna. As modules
pose no other high frequency signal coupling to the antenna, RX sensitivity is thus not influenced
except when crystal oscillators are set near the antenna, or UART TX and RX conducts through RF
trace lines. If ESP8266EX serves as slave, there will be quite a number of high frequency interference.
Therefore, signal interference depends on board design.
Solution: keep the antenna away from crystal oscillators and keep RF trace lines away from high
frequency signal.!
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