Author
Donald Gardner
This blog post originally appeared on Antenna Systems & Technology.
Microwave antennas form an essential part of modern mobile communication networks, providing the majority of backhaul provision between cell sites and core networks. In common with the rest of the network, there is a lot of pressure to minimize the costs of microwave network rollout. Some choose to do this through the use of cheap antennas; however, this can actually cost more in the long-run when the total cost of ownership (TCO) is considered. Let me explain by first reviewing some of the factors that drive cost in a microwave antenna.
Antenna Design and the RF Path
The design of a microwave antenna breaks down into two broad areas—although there is some overlap between them. The first of these is the RF path, which mainly comprises the feed system, the reflector and the radome. Assuming the antenna is correctly designed, the key driver to consistent performance is control of shape, symmetry and size. Failure to accurately control the shape of various components will mean the antenna will not deliver the required gain, pattern, cross-polar performance (XPD) and return loss.
Similarly, failure to control the symmetry of the antenna means the antenna will not be uniformly illuminated; this has a major impact on pattern, XPD and—in the worst cases—antenna gain. Where the size requirements are not maintained, components will not assemble correctly, leading to potential RF leakage and loss of pattern compliance.
From the above, it can be seen there are several key cost drivers for microwave antennas:
- Components must be designed to proper tolerances to ensure that RF performance requirements are achieved.
- The relationship between components must be tightly controlled to guarantee RF performance.
- The overall design must be stiff enough to ensure that items 1 and 2 above are maintained over the operational performance envelope of the antenna.
Poor manufacturing processes result in noncompliance to specification. The figure shows a tested non-CommScope product that breaches regulatory specifications in several places. Further analysis indicated that, in addition to poor manufacturing processes causing the issues in the 0-90 degree region (blue arrows), compromises in the design—presumably for cost purposes—meant that, in the 90-180 degree region, the antenna would not be able to meet regulatory specification despite compliance being claimed.
It is not realistic to measure every microwave antenna electrically for all parameters during the manufacturing process, since this requires the use of a test range. Instead, reliance is placed on measurement of mechanical characteristics such as compliance of reflector shape to tolerance as well as electrical tests such as return loss. To support this, a random sample of factory production is then subjected to full electrical test—the same tests as used to verify the initial design - to ensure that all product consistently meets specification.
Total cost of ownership
Total cost of ownership (TCO) involves much more than the cost of the antenna itself. It also includes the initial costs of site acquisition; tower or mast requirements; electronic equipment such as radio, antennas and installation; as well as the ongoing operational cost of the network.
Over the full life of the antenna, the antenna purchase price is, in fact, a very small percentage of the TCO. However, attempting to identify and remedy poor performance in the network caused by antennas not meeting performance is likely to be extremely expensive. The costs associated in deploying field crews alone may be an order of magnitude larger than any initial antenna cost—even before the costs in lost traffic are taken into consideration.
Thus, we arrive at one of the issues inherent in any large organization: different parts pursuing potentially conflicting goals. The purchasing group may be pursuing a minimal total capital spend; however, without a full awareness of the parameters of the product they are purchasing, initial savings may result in a far greater negative impact elsewhere in the organization. No one would claim that initial capital costs are not important; it is absolutely essential that they are fully controlled. However, it must be done in the context of total rather than simply initial cost.
The question then is how this can be done. The solution is relatively simple—all items in the backhaul chain must be treated with due diligence rather than as commodity items purchased in isolation. It means knowing the provenance of all such equipment—that is, who actually manufactures it, to whose designs, and under what system of controls. Only this broader understanding reveals TCO and facilitates smart spending decisions.
