Phil Kurz /
08.19.2010 10:51 AM
Look to nature to find better DTV antenna performance, report says

What do foraging bacteria, invasive weeds, hungry ants looking for a quick meal, swarming fish in search of food and even genetics have to do with ways to optimize set-top antennas to receive over-the-air digital television? Quite a lot, actually, according to a revised report released this week by the NAB.

The 131-page document, "High-Performance Indoor VHF-UHF Antenna Technology Update Report," prepared for NAB's Science and Technology Department by MegaWave, in Devens, MA, presents various advancements in the antenna design aimed at improving DTV reception in the home.

Since the completion of the DTV transition in June 2009, some broadcasters transmitting on low VHF channels have lost OTA audience and taken various steps to remedy the problem, including requesting channel reassignment in the UHF band.

The report examines 10 existing candidate design methods and technologies with the potential to improve indoor antenna reception of DTV signals between 54MHz and 698MHz. To illustrate the problems associated with indoor OTA antennas, the report points out that "a half-wavelength in the low VHF TV band varies between 9.2 and 5.6 feet." The length of a dipole antenna shorter than its wavelength divided by pi is an "electrically small antenna," which inherently has a narrow bandwidth and low gain. If the longest acceptable indoor antenna is 2ft to 3ft in length, acceptable performance will be difficult to achieve across the full TV spectrum, the report said. Add to that other disadvantages, such as nearby RF noise and signal loss due to building penetration, and the severity of the problem becomes clear.

Enter the bacteria, ants, weeds, fish, genetics and a number of other nature-inspired optimization methodologies that can be used to generate antenna designs "that are impossible to achieve otherwise," the report says. While optimizing an antenna and foraging bacteria may seem disparate, "there is a connection, at least in the sense that bacteria finding a good food source is similar to finding an antenna with a good gain-bandwidth product," the report says.

Labeled "metaheuristic" to convey that it's both empirical and conceptual in nature, an optimization algorithm based on foraging bacteria "can be implemented in many different ways because the bacteria foraging metaheuristic simply suggests an analogy to Nature that is implemented in a computer algorithm working on an antenna problem," according to the report.

Since 1995 when MegaWave developed a broadband VHF/UHF set-top antenna, a "plethora of new optimization algorithms" have been developed and put into use, it says. These algorithms can solve problems "that have no analytical solutions or are too complex to apply traditional analytical techniques," the report adds.

In addition to describing several nature-inspired optimization algorithms, the report details other areas of work being done that can improve antenna performance, including active RF noise cancelling, the use of metamaterials in antenna design and retrodirective arrays.

The report recommends the NAB consider "developing a computer generated/optimized broadband dipole antenna element" to show "it is feasible to design a VHF/UHF antenna system that is both simple, have positive gain, be of reasonable size and weight" and not need a CE-909-A interface to obtain channel designator of signal quality information from the DTV receiver, it says.



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