Antenna Systems & Technology - Summer 2016 - (Page 22)

GUEST COLUMN The Unexpected Cost of Low Cost Microwave Antennas By Donald Gardner | CommScope 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: 1. Components must be designed to proper tolerances to ensure that RF performance requirements are achieved. 2. The relationship between components must be tightly controlled to guarantee RF performance. 3. 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. Figure 1 shows a tested nonCommScope product that breaches regulatory specifications in several places. Further analysis indicated that, in addition to poor manufacturing processes causing the issues in the 0 to 90° region (blue arrows), compromises in the design, presumably for cost purposes, meant that in the 90 to 180° 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. Figure 1. Testing reveals a radiation pattern (RP) outside of specification, rendering the antenna noncompliant. 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. 22 Antenna Systems & Technology Summer 2016 www.AntennasOnline.com http://www.AntennasOnline.com

Table of Contents for the Digital Edition of Antenna Systems & Technology - Summer 2016

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Components/Subsystems
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The Unexpected Cost of Low-Cost Microwave Antennas

Antenna Systems & Technology - Summer 2016