When I attended Cornell University in 1976 and 1977 for my master’s degree, I took a microwave lab course. In the lab room where we worked was a large glass desiccator jar, sort of like a clear cookie jar with blue desiccator crystals in the bottom to keep the contents dry. Inside the main area of the jar were tiny rectangular copper pipes with little connectors on the ends. The pipes were about a quarter of an inch wide or less, some as small as soda straws, and a few inches long. When I asked one of the professors what this was, he explained that the pipes were millimeter-wave waveguides. Certain frequencies of millimeter waves were highly absorbed by water, so they had decided to keep the waveguides in a desiccator jar to make sure that they didn’t have any absorbed film of water in them that would mess up the measurements they might make with them.
Back then, millimeter-wave equipment was nothing more than a laboratory curiosity. In terms of frequencies, millimeter waves range from 30 GHz up to 300 GHz. Their name comes from the fact that they make waves in air that are between 1 and 10 millimeters long from one peak to the next peak. Back in the 1970s, they were extremely hard to generate and detect, and nobody but a few scientists had anything to do with them. The only large corporation that had pursued serious research about millimeter waves was Bell Laboratories, which thought for a while that the future of their network would involve millimeter-wave waveguides crisscrossing the country. But when Corning and other companies figured out how to make extremely low-loss optical fibers, Bell dropped their millimeter-wave idea and switched to fiber optics, which is how the vast majority of network traffic travels today.
But you can’t attach fiber optics to a moving car, or somebody walking down the street, so as newer applications such as virtual reality and the Internet of Things grow, there is a constantly increasing need for more wireless bandwidth. And millimeter waves will be a key player in the next generation of wireless network technology called 5G.
Last Friday, Apr. 12, the U. S. Federal Communications Commission (FCC) announced that it plans to auction off close to 5 GHz of some millimeter-wave bands that have previously been reserved for other purposes. These bands are at 37, 39, and 47 GHz. For many years now, auctions have been the FCC’s preferred method of allocating frequencies to private entities, and while such auctions shut out everyone except those well-heeled enough to afford to exploit the frequencies they buy, this process is a lot more transparent and fair than their former practice of simply opening applications to all comers, and waiting to see who gets there first. And the old process was often subject to political log-rolling. For example, the way Lyndon B. Johnson obtained control of station KLBJ in Austin and vastly mproved its value in the 1940s does not bear a lot of scrutiny, unless you don’t mind finding a lot of political wangling that the then-senator engaged in with the FCC.
While auctions of radio spectrum allocations are not inherently just proceedings in themselves, they do acknowledge that the spectrum is a limited natural esource, and an auction allows interested parties to express their perceived value of that resource in bids. We don’t often value what we don’t pay for, and so an auction tends to ensure that whoever gets the right to use certain frequencies is going to exploit them so as to get their money’s worth.
Even as recently as a decade ago, an auction of millimeter-wave bands wouldn’t have attracted much attention, because the technology to generate and receive such waves was way too expensive for consumer products. But with advances in fabrication methods, microwave technology, and adaptive control of antennas, it’s now feasible to start building the micro-cells that millimeter-wave wireless will need. As you go higher in frequency to around 60 GHz, millimeter waves are increasingly absorbed by oxygen in the air, and even below that frequency they do not propagate very far compared to the longer microwaves that are used for earlier wireless systems. So this means we will need a whole lot more millimeter-wave base stations than you would need for equivalent coverage at lower frequencies.
A millimeter-wave base station won’t be a two-hundred-foot tower with antennas several feet long hanging from the top. It will probably take the form of a box or panel just a few feet square, sitting at or near ground level, typically on a utility pole. They will show up first in big cities where the density of foot and vehicle traffic justifies the installations, and then less dense areas will be covered. For sparsely populated areas, the FCC has announced it is thinking about allocating some frequencies as low as 600 MHz, whose waves can cover much wider areas, so suburbs and rural regions won’t be totally left out in the cold, wireless-wise.
This all assumes that there’s nothing harmful to human health regarding the increased amount of millimeter-wave radiation that people will be subjected to as 5G deploys. There is at least one person with apparently good qualifications who says this isn’t so. Martin L. Pall is a retired professor of biological sciences at Washington State University who has published both refereed journal papers and popular talks saying that Wi-Fi, and in particular millimeter waves, can cause everything from low sperm counts to cancer. I know enough about electromagnetics to have reason to doubt some of his reasoning as to how this occurs, but interested parties can examine his case here. If he’s right, we ought to go slow on the rollout of 5G, but it looks like instead we’ll be performing a massive experiment in which millions of people get exposed—and then we’ll see if anything bad happens.
Sources: The FCC’s news release about their planned 5G auction can be found at
https://docs.fcc.gov/public/attachments/DOC-356984A1.pdf. I read about the plan in an Associated Press article carried by the Austin American-Statesman on Apr. 13, a version of which can be viewed at the AP website https://www.apnews.com/402d7c2651914d31a4f216f81eadda53. Dr. M. L. Pall’s expression of his concerns regarding the increasing use of Wi-Fi can be read in his paper in Environmental Research vol. 164, pp. 405-416 (July 2018), which is downloadable at https://www.sciencedirect.com/science/article/pii/S0013935118300355.