Electronic Design

What's So Special About The White Space And 700-MHz Bands?

The newly available spectrum lies in the UHF range (300 to 3000 MHz), which is prime territory for wireless. Most unlicensed spectrum is microwave (902 to 928 MHz, 2.4 GHz, 5 GHz, 60 GHz). That spectrum works well, but doesn’t match the efficacy of bands below about 900 MHz. Why? Physics.

The lower the frequency, the longer the potential range of a radio signal for a given power level, antenna gains, and other factors. Lower frequencies naturally travel farther given a direct line-of-sight (LOS) path. On top of that, they penetrate obstacles like walls, trees, and vehicles better than microwaves. This translates to greater communications reliability as well as more favorable indoor use.

In broadband or cellular applications, lower frequencies result in fewer basestations for a certain amount of area coverage. Also, UHF signals are less affected by the multipath reflections that plague microwaves. Finally, the semiconductor technology is easier at UHF than microwave, making ICs inexpensive and easy to make.

About the only downside is that the lower frequencies require longer antennas for good communications. Whereas microwave antennas are inches long, UHF antennas are about a foot or longer. The antenna manufacturers should take care of that problem.

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