The quality of an RF signal should not be degraded when there is no ESD event

For the received signal, it suffices to consider the attenuation of the signal level. For the signal to be transmitted, it is also important to ensure that it will not become distorted. It is necessary to consider harmonic distortion for modern modulation methods such as 16-QAM and 64-QAM* that modulate both phase and amplitude.
For signal attenuation, consider the band of the low-pass filter formed by parasitic capacitance. In other words, it is desirable to use ESD protection diodes with low capacitance. Ideally, the maximum signal frequency should be about one-fifth of the cut-off frequency.
Harmonic distortion** should be linear with respect to the amplitude level. Since an RF signal generally swings across the GND level at the antenna end, choose a bidirectional ESD protection diode that provides symmetrical voltage swings around the GND level. It is also important to ensure that the ESD protection diode does not enter breakdown when a signal with a large amplitude is applied. In other words, the working peak reverse voltage (VRWM) of the ESD protection diode should be higher than the maximum input amplitude level.
In addition, the operation of an ESD protection diode is dependent on voltage since it has parasitic junction capacitance. It is therefore desirable to choose a low-capacitance diode whose capacitance does not change much with voltage.

To recap, select ESD protection diodes that:

1. have low capacitance;
2. are bidirectional;
3. have VRWM higher than the maximum signal amplitude; and
   
4. exhibit a small change in capacitance.