Answer: When these waves move towards us, the frequency of these waves increases.
Step-by-step explanation:
Electromagnetic waves are the waves which does not require a medium to travel. They propagate through the space and can travel in vacuum also.
Microwaves are electromagnetic waves used in broadcasting and telecommunications. When these waves travel towards us, the wavelength of these waves decreases and hence, increases the frequency of the waves.
Wavelength and frequency follow inverse relation, which is:

where,
= frequency of the wave
= wavelength of the wave
As, the wavelength decreases, frequency increases and vice-versa.
Hence, when these waves move towards us, the frequency of these waves increases.