There's only one part of a radio that touches the medium upon which the radio operates, and that's the antenna. We tend to pay little attention to antennas, but they are the component responsible for putting a signal on the air at the transmitter and getting it back off the air at the receiving end. Radios are like the tires on a car: The tire is the only part of the car that touches the road, the medium upon which the rest of the vehicle operates. And, as any driving enthusiast knows, picking the right tire can have a profound impact on how the car handles. Great tires, great ride. Great antenna, and there's a much better chance that the rest of the radio can meet specifications under a wide variety of operating conditions.

In fact, many of the innovations that in recent years have enabled wireless to push the performance envelope have been the result of improvements in antenna technologies. MIMO, or multiple-input, multiple-output, which is now perhaps the most important technology in WLANs, uses multiple antennas (and a lot of signal processing) to improve throughput and range, and we'll eventually see MIMO in WiMax and cellular implementations as well.

Of course, there are a few issues yet to be resolved in the broad adoption of MIMO. Among these are cost, power consumption and the physical real estate required in a product using MIMO. But I think MIMO will be so valuable that engineers will quickly address these concerns. Even in more traditional radio implementations, antenna innovations abound, with many coming from formerly military applications. For an example, visit Skycross' Web site.

One of the more interesting directions for antennas has been in what are known as distributed antenna systems (DAS). These are of particular interest in larger enterprises, and especially to those with larger buildings. The idea is to centralize the radios themselves, whether they are in the form of cellular base stations, public safety systems, wireless LANs or almost any other wireless system. The DAS then extends the antennas for these systems potentially quite far away from the radio itself. This can be done over a fiber connection, but the idea is to run just one wire in various parts of the building and thus support multiple radios with minimal installation expense.

This technique can be a bit controversial when it comes to wireless LAN access points. After all, isn't it simpler to just plug the APs into spare RJ45 connector and avoid the whole installation effort altogether? While this approach can work well in most open-office enterprises, there are other venues -- in fact, any that have fundamentally public access -- where it just isn't appropriate to leave an AP out and exposed. And, assuming that one wants to bring cellular or other wireless coverage to these areas as well, a DAS can make a lot of sense.