Now, here's a thing:
Air, as opposed to a vacuum, has a different refractive index from the refractive index of a vacuum. Nominal refractive index for air is 1.000273 compared to 1 for a vacuum.
The speed of light in a medium is inversely proportional to its refractive index.
But the refractive index is dependent on wavelength. That is to say, different wavelengths meet different "resistance" in the same medium. This means that different wavelengths travel at different speeds in the same medium, eg, air. Think of a prism.
So increasing the frequency (reducing the wavelength) of radar transmissions means the shorter wavelength (higher frequency) radar signals do travel faster than the longer wavelength radar waves of yore. But you'd need to be quick with a stopwatch to measure the difference over a 200 m roundtrip.
https://en.wikipedia.org/wiki/Refractive_index#Dispersion
The refractive index of materials varies with the wavelength (and frequency) of light.[28] This is called dispersion and causes prisms and rainbows to divide white light into its constituent spectral colors.[29] As the refractive index varies with wavelength, so will the refraction angle as light goes from one material to another. Dispersion also causes the focal length of lenses to be wavelength dependent. This is a type of chromatic aberration, which often needs to be corrected for in imaging systems. In regions of the spectrum where the material does not absorb light, the refractive index tends to decrease with increasing wavelength, and thus increase with frequency. This is called "normal dispersion", in contrast to "anomalous dispersion", where the refractive index increases with wavelength.[28] For visible light normal dispersion means that the refractive index is higher for blue light than for red.