Foreword

The development of computer programs for modeling antennas began in the 1960s when main-frame computers were making advancements. Modeling codes that could run on desktop computers made their appearance in the early 1980s. The design of directional antenna arrays for medium-frequency (MF) broadcasting stations has a much longer history, however, reaching back to the mid-1930s when computations were done using a slide rule.

In the early years, methods involving approximations (such as the assumption of sinusoidal current distributions on the radiators) were developed and broadcasters have used them with reasonable success up to the present day. For the most part, however, to do that work the broadcaster's use of the computer has been relegated primarily to arithmetical operations rather than to actual modeling of the antenna. The success of simple design methods, and the fact that the generalpurpose modeling codes and broadcast antenna engineers sometimes seem to “speak a different language,” may account for the somewhat slow adoption of computer modeling by the broadcast community.

J.L. Smith has extensive experience in directional antenna design, which began long before the development of computer modeling. In Basic NEC with Broadcast Applications, he describes methods he has developed to use the public domain NEC-2 modeling code to design and tune MF directional antenna arrays. Some of the methods parallel the techniques developed by the navy's antenna designers by starting with simplified models and sometimes adjusting the models to match measurements. By using these methods, model parameters can be varied or features can be added to study effects.

In teaching courses on antenna modeling, we have found that new users often start by trying to model with too much detail. As a result, they run into problems with code limitations and eventually produce a large model that takes a long time to run and makes it difficult to try variations. Smith shows how to start with simple models, how to allow for code limitations and still get the important information. He illustrates the effectiveness of his methods by eventually comparing model results to measurements.

This book should be useful for both the beginning student and the working broadcast engineer. Beyond learning the methods described, you will be encouraged to see that it is possible for an ordinary user to get valuable results from the free public domain NEC-2 computer code.

Jerry Burke

Livermore, California