In the telecommunications world, a point-to-point link connections is, quite simply, a connection between two nodes (endpoints) that are some particular distance apart. There is always a maximum usable distance and there is also always a minimum spacing required between endpoint point-to-point radios. In the context of WiFi, microwave, millimeter wave, licensed, and unlicensed wireless point-to-point bridge link engineering the link is referred to as a "Layer 2 Link" or, simply, an "L2" link. Design engineering, installation, configuration, and testing wireless L2 links has common requirements and tasks which, while they might be performed with some differences, meet the same overall objectives no matter which vendor's equipment is being deployed.

There are a number of Connect802 Technical Information pages and articles as well as Connect802 Services focused on antennas and point-to-point architecture, design engineering, consulting, and installation support..

System planning is critical to the successful installation, operation and proper performance of any communication system, wireless systems are no exception, and this is especially true for line-of-sight (microwave) wireless. Unless your proposed microwave link will be operating over a very long path, you should be able to confirm whether a visible line-of-sight path exists between the two proposed antenna sites. This is only a first-step process, and is often accomplished by using a combination of strobe lights, mirrors (which reflect the sun), binoculars and spotting scopes. Being able to see one site from the other will not guarantee that the visible path is appropriate for a microwave signal, but at least you who know that the possibility of such a path exists.

"Line-of-sight" is a term used in radio system design to describe a condition in which radio device antennas can actually see each other. High frequency radios, such as those used in Bridgewave Wireless, Siklu Wireless, and Ruckus Wireless 802.11 point-to-point radio links require line-of-sight between antennas.

In many instances there may be obstacles to overcome such as buildings, trees, small hills and elevated roads, and it may not be possible to confirm that line-of-sight exists without additional aid. Keep in mind that even a "perfectly clear" visual path may not actually be so. As an example, small branches of deciduous trees, barren in the winter, may not be visible until spring or summer when growth appears. Even the skeleton of a new building may not be visible until the sides go up! Establishing line-of-sight for traffic signal systems should be easy to accomplish because of the short distances involved (a few blocks).

When establishing line-of-sight, it is extremely important to plan for the future. In urban areas, new building construction may result in total path obstruction. In areas where construction is not anticipated, the rapid growth of trees or foliage may severely affect the path over time. While a number of software products are available for assisting with path work, combining a topographical mapping of the path with a subsequent path walk or drive is often an excellent way to start the line-of-sight confirmation process.

Assuming an appropriate line-of-sight path from radio site to radio site can be established, both the feasibility and viability of a point-to-point microwave radio link will be dependent upon the gains, losses and receiver sensitivity corresponding with the system. Gains are associated with the transmitter power output of the radio, and the gains of both the transmitting and receiving antennas. Losses are associated with the cabling between the radios and their respective antennas, and with the path between the antennas. Other losses can also occur if the path is partially obstructed, or if path reflections cancel a portion of the normal receive signal. Manufacturers will state respective RF power output and gain for each of their products.

One of the first items to consider for any microwave path is the actual distance from antenna to antenna. The further a microwave signal must travel, the greater the signal loss. This form of attenuation is termed free space path loss (FSPL). Assuming an unobstructed path, only two variables need to be considered in FSPL calculations:

A signal transmitted at a frequency of 6 GHz will have more available power than a signal transmitted at 11 GHz. For example, a microwave system at 6 GHz can expect to cover about 25 miles between communication points. The same system using a frequency of 11 GHz will only cover about 10 miles.

When RF energy is transmitted from a parabolic antenna, the energy spreads outward, much like the beam from a flashlight. This microwave beam can be influenced by the terrain between the antennas, as well as by objects in or along the path. When the centerline of a beam from one antenna to another antenna just grazes an obstacle along the path, some level of signal loss will occur due to diffraction. The amount of signal loss can vary dramatically, influenced by the physical characteristics and the distance of the object from the antenna.

A microwave beam can also be reflected by water or relatively smooth terrain, very much in the same way a light beam can be reflected from a mirror. Again, since the wavelength of a microwave beam is much longer than that of a visible light beam, the criteria for defining "smooth terrain" is quite different between the two. While a light beam may not reflect well off of an asphalt road, a dirt field, a billboard, or the side of a building, to a microwave beam these can all be highly reflective surfaces. Even gently rolling country can prove to be a good reflector.

A microwave beam arriving at an antenna could effectively be canceled by its own "mid-path" reflection, causing tremendous signal loss. Long microwave paths can also be affected by atmospheric refraction, the result of variations in the dielectric constant of the atmosphere.

For relatively short 2.4GHz microwave paths, only reflection points and obstructions are usually of real concern. The effects of atmosphere and earth curvature will not usually come into play, so the engineering of these paths is quite straightforward. For long or unusual paths, however, all aspects of path engineering must be considered.

Microwave radio systems are among the most interference tolerant communication networks in use today. Point-to-point connections using very narrow beamwidth (3.5-degrees or less) signals are very difficult to detect and, by their nature, are highly resistant to jamming and interference. 

All RF systems have an antenna (or several in an array). The transponder used in a vehicle for toll collection has an antenna. The fact that it can't be seen doesn't mean that it isn't present. The antenna is built in-to the package. A cost comparison of all the elements that make up a radio system would show the antenna as the lowest cost piece. However, most of the problems that a radio system may have can be traced to either improper installation, or improper selection, of the antenna. Follow best-practices for placement and installation to avoid subtle problems.

All antennas have similar characteristics. They are designed with vertical and horizontal polarity. The manipulation of these characteristics creates a specific antenna coverage pattern. Some antennas are designed to provide a circular pattern referred to as omni-directional. Others have an elliptical pattern referred to as uni-directional. A directional antenna typically projects two (or more) highly directional lobe patterns. When setting up a radio system, it is critical that the installers match the pattern lobes to the system design. If the direction of the lobes is off by just a few degrees, that may cause the system to have a marginal performance.

RF Transmission cable should be treated with the same care as fiber optic communication cable. This is important. To prevent interference with other radio systems on the tower the transmission cable is constructed with an internal shield of copper or copper foil. If this shield is broken, your system could cause interference with other systems at the site. Also, once the shield is cracked, your system is subject to interference. Some radio transmission cable uses a hollow copper tube to act as a "wave guide". If the hollow tube becomes damaged your system might not function properly. The following guidelines apply: