```
f = c / λ
```
Where:
* f is the frequency in Hertz (Hz)
* c is the speed of light (299,792,458 meters per second)
* λ is the wavelength in meters
In this case, the wavelength is 20 centimeters, which is equal to 0.2 meters. So, the frequency of the radio wave is:
```
f = 299,792,458 / 0.2 = 1,498,962,290 Hz
```
Therefore, the frequency of the 20cm radio wave is approximately 1.5 GHz.