MILLIMETER MICROWAVE (mmWave):
Conventional microwave backhaul links employ mostly the lower end of this range—from 1 GHz up to 42 GHz. But there’s a lot of spectrum above that, and it’s becoming increasingly attractive as a means of providing backhaul: millimeter microwaves, or mmWave.
There are two bands used in LOS link applications: E-band and V-band. E-band covers 10 GHz of spectrum in two separate ranges—from 71 GHz to 76 GHz and 81 GHz to 86 GHz; V-band covers 7 GHz in one band from 57 GHz to 64 GHz. However, V-band can be expanded to reach an upper range of 66 GHz, increasing its spectrum to a total of 9 GHz overall. E-band is more commonly used in microwave backhaul for reasons that will be discussed later. The main advantage of mmWave bands over commonly used lower-frequency microwave bands is capacity. It is now considered the best choice for point-to-point microwave links because it offers more spectrum and more bandwidth than lower frequencies, an important feature for operators struggling to keep up with skyrocketing user demand for data on 4G LTE networks.
Like lower-frequency microwave antennas, mmWave antennas support capacity enhancement options like dual polarization with the efficient integrated radio configurations. This lets operators move more data without minimal additional infrastructure. This highcapacity, high-reuse scheme gives mmWave systems extremely attractive TCO helped by the characteristics of the antenna.
Even with all these advantages, mmWave antennas must be built to high quality standards to optimize their performance and capacity. A quality antenna will feature an RPE compliant to ETSI Class 3 specifications or better—guaranteeing that its RF energy will stay contained to a single beam along the link path, as show in Figure below:
Another feature contributing to its attractive TCO profile is the fact that mmWave is relatively easy and inexpensive to license. Most regulatory bodies impose only a low, one-time fee or no licensing at all. Considering the large costs of spectrum licensing in sub 40 GHz frequency bands, this is a significant advantage. The downside to this is the question of availability. Being only lightly licensed or not at all, the proliferation of mmWave links raises the very real possibility of interference. Again, the build quality of the antenna is critical: a Class 3 or better RPE will minimize any role interference has in a mmWave link because a tightlycontrolled radiation pattern not only directs RF energy with more precision, it is also more discriminating in which RF energy it will accept.
One limitation associated with V-band mmWave is the fact that V-band frequencies are readily absorbed by oxygen in the atmosphere, so link lengths are restricted to about one kilometer or less.
However, the inherently high capability for frequency reuse—combined with its small footprint—means that V-band antennas still have an important role to play in a backhaul network. E-band, in contrast, does not have the same issue of oxygen absorption as V-band does, making it a smart choice for links several kilometers long, and a likely candidate for upgrading existing conventional microwave links, since mmWave bands can deliver Gbps capacity.
Although the higher frequencies deliver higher gains for a given antenna size, the atmospheric attenuation limits the range of these antennas. This is not an issue in dense urban networks, where links are typically very short, allowing the deployment of very small, inconspicuous antennas, that may even be embedded in the radio itself.
The smallest conventional microwave antennas can be pretty small—about 0.3 m (1 ft). mmWave antennas, on the other hand, offer ultra-low profiles in sizes as little as 12 cm (5 in) across
->>mmWave represents an incredible advance in pointto-point microwave communications. Leveraging the versatility of LOS links, mmWave systems provide capacity and reliability comparable to fiber-optic connections that are often difficult, expensive or even impossible to link to a needed location. To realize the capacity, efficiency and TCO advantages of mmWave, however, it’s vitally important to choose a quality antenna compliant with ETSI Class 3 or better, or interference can put the brakes on a much faster, more powerful and reliable backhaul network.
mmWave frequencies are higher than conventional microwave systems
• E-band: 71–76 GHz and 81–86 GHz • V-band: 57–64 GHz, expandable up to 66 GHz
• Characterized by antennas with narrow beams and high spectrum reuse
• Easier to license than conventional microwave
• Build quality extremely important: ETSI Class 3 or better
• V-band for short links of 1 km or less; E-band for longer links or upgrades
This is the emergency of 5G mmWave
References:
Internet and MicroWave Transmission Book
