As can be seen in the picture above (from our Masterclass), the Millimeter wave starts from around 30GHz.
Millimeter waves occupy the frequency spectrum from 30 GHz to 300 GHz. They’re found in the spectrum between microwaves (1 GHz to 30 GHz) and infrared (IR) waves, which is sometimes known as extremely high frequency (EHF). The wavelength (λ) is in the 1-mm to 10-mm range. At one time this part of the spectrum was essentially unused simply because few if any electronic components could generate or receive millimeter waves.All that has changed in the past decade or so. Millimeter waves are now practical and affordable, and they’re finding all sorts of new uses. Best of all, they take the pressure off the lower frequencies and truly expand wireless communications into the outer limits of radio technology (see the table). If we go any higher in frequency, we will be using light.
Millimeter waves open up more spectrum. Today, the spectrum from dc through microwave (30 GHz) is just about used up. Government agencies worldwide have allocated all of the “good” spectrum. There are spectrum shortages and conflicts. The expansion of cellular services with 4G technologies like LTE depends on the availability of the right sort of spectrum. The problem is that there isn’t enough of it to go around.As a result, spectrum is like prime real estate—it’s expensive. And the expression “location, location, location” is apt for spectrum. Millimeter waves partially solve the problem by providing more room for expansion. You can take all of the useful spectrum we now use from dc to 30 GHz and drop it into the lower end of the millimeter-wave region and still have 240 GHz left over.
You can read the complete article here that gives lot more details.