What should be clear is that one’s choice of microwave antenna has an enormous impact on how well—and how long—it performs in a real-world deployment. While only a small part of the overall investment, antennas cover a range of costs that bear directly on their quality and reliability.
The purpose is to select an antenna that optimizes ROI.
There are several factors to consider when choosing a microwave antenna and planning a link. They range from technological considerations to financial ones— each playing a part in calculating the value one can expect in return for the investment. These factors include:
The electromagnetic environment and degree of radio congestion in the link area
The link’s capacity requirements, and whether they will need to be maximized
Environmental conditions in the link area
The nature of the available infrastructure for antenna installation
Physical access to the site for installation, commissioning and maintenance • Available installation budget and TCO targets over the life of the antenna
Other factors—such as the antenna type, size and operation frequency—are defined as part of the detailed RF analysis and the planning of the link. A wide variety of antenna types are available to suit virtually any requirements. They can range in size from a few centimeters to more than four meters in diameter; and they can support typical operation frequency bands from 3 GHz to 90 GHz.
The study of radio wave propagation through the atmosphere is a vast topic all by itself. Generally speaking, the rules are that:
Lower frequencies allow for longer links than higher frequencies
Larger antennas transmit a signal farther than smaller antennas at the same frequency
These rules are limited by other practical considerations in the link, such as the degree of antenna alignment possible in a real-world deployment and the narrow beamwidths involved with larger antennas. When selecting an antenna, the link planner must know:
How long the link must be. That is, how far apart the two LOS endpoints are. This information can be obtained from map data.
The available frequency. This may be determined by local regulators, a third-party coordination body, or based simply on which frequencies the operator owns.
Performance requirements. This can be measured as link throughput (in mbs) and link availability, expressed as a percentage of uptime. If the radio supports it, the link’s capacity and availability can be scaled dynamically—trading one for the other as needed.
With these parameters in hand, the planner can determine the amount of gain required from the antenna and, with reference to manufacturer literature, its approximate diameter. This is where the process begins, but there are several other important steps before a final antenna choice can be made.
Every antenna deployed in a point-to-point microwave network should have a published RPE, providing a measurement of the antenna’s ability to discriminate against unwanted signals—that is, interference. This ability is measured over a plus/minus 180-degree azimuth angle relative to the antenna’s boresight, or aimed direction.
Historically the best performing antennas (such as UHX antennas from CommScope) had assymmetrical RPEs. In these cases antennas had to be carefully installed to ensure that the feed orientation matched the path specification. Modern design tools have led to the development of even higher performing antennas such as the Sentinel and USX antennas from CommScope. These have symmetrical patterns that are better than the old assymmetrical ones. In all cases, quality antennas from responsible manufacturers will declare and demonstrate RPE compliance with regulatory standards published by such bodies at the FCC and ETSI.
Now, Let’s look at some of the basic antenna solutions made by CommScope for microwave links:
Unshielded parabolic antennas. These were historically used in areas of low radio congestion with little need for tightly engineered RPEs. These are now rarely deployed and are being slowly discontinued.
Enhanced performance standard parabolic antennas (PAR). These unshielded antennas meet FCC Category A compliance for use in networks in the United States. With increasing radio congestion and the cost effective availability of better performing alternatives, the deployment of these antennas is diminishing.
High-performance antennas. These meet or exceed ETSI Class 3 radiation pattern performance standards. They are available in single- and dualpolarized versions. They are typically provided with shields or shrouds, but recent advances in technology have made the same RPE possible without shields. Low profile antennas have generally replaced shielded antennas of less than 1.3 m (4 ft) in diameter.
Ultra-high-performance antennas. Providing high-gain, low-VSWR radiation patterns, these antennas minimize frequency congestion and simplify frequency coordination due to their highlyefficient beam-forming feed assembly. They are available in dual-polarized (UHX®) and singlepolarized (UHP®) configurations.
High cross-polar discrimination antennas. These antennas feature very high cross-polar discrimination, making them a good choice for co-channel transmission. CommScope’s HSX antenna offers 40 dB of discrimination, tight RPE and low side lobes for high-capacity needs in congested areas.
Ultra-high-performance high cross-polar discrimination antennas. The latest designs of antennas provide the best possible RPEs combined with very high cross-polar discrimination to maximise link availability and network density. Examples include CommScope’s USX antenna range.
ValuLine antennas. Meeting and exceeding ETSI Class 3 standards, these small-diameter, highperformance antennas are used all over the world in short-haul backhaul applications. Available in single- or dual-polarized configurations, they are built in diameters up to 1.8 m (6 ft) and frequencies up to 80 GHz.
Sentinel® antennas. Extremely low side lobe antennas meet ETSI Class 4 performance standards due to their superior RPE characteristics and high immunity to interference. This allows high levels of frequency reuse, amounting to 40 percent more than a comparably-sized Class 3 antennas. They also take advantage of advanced radio features like adaptive coding and modulation (ACM) that boosts capacity and availability. CommScope’s Sentinel solution is a state-of-the-art Class 4 antenna; its small size makes it easy and inexpensive to ship and install.
ROI is realized in a balance between cost and performance
Smart antenna decisions take a deep understanding of the link’s needs
A wide choice of antennas exists to suit specific applications, needs and conditions
Up to 70 percent of antenna TCO comes after the initial investment
Class 4 antennas represent a major advance in capacity and efficiency over Class 3 antennas— potentially, greatly reducing TCO
Summarry:
The technology of microwave backhaul must serve the larger demands of an operator’s business. While there are many steps involved in determining the right antenna for a given application, the correct choice is not always the obvious (or least expensive) choice. Backhaul is a critical part of the wireless industry, and, like every other dimension, ROI is the final, most dependable metric that measures the value of each dollar spent.
When you know your antenna options—as well as the other issues that proceed from those options—you can increase that value and avoid unpleasant surprises down the road.
Reference: Internet and Microwave Communication Basics Book
