The search for a compact directional antenna that provides coverage of the entire 10-meter band has gone on since 10 meters was opened to amateur operations. So I wondered if I could design one, using some of the more recent concepts and tools available for antenna work. Among the tools are antenna modeling software, such as NEC and MININEC, and some antenna calculating utilities, like LPCAD. One of the more promising antenna concepts for covering all of 10 meters is the Log Periodic Dipole Array, or LPDA for short. Most LPDAs cover a wide frequency range and they require some careful selection and adaptation for monoband use. Although the LPDA is the primary focus of this collection of notes, some wide-band Yagi ideas are also worth investigating, for example, the use of open-sleeve coupled drivers.
To make the project more interesting, I set some goals for myself in the form of design objectives. Since we can design a short-boom (8") 3-element Yagi to cover half the band with 7 dBi free space gain and a 20 dB front-to-back ratio, these same boom length, gain, and front-to-back figures became criteria for successful design. Of course, the antenna--either directly or via a matching system--must provide less than 2:1 SWR to the system's 50-Ohm main feedline across the entire band.
The notes in this collection record as much the process of thinking I went through in finding a satisfactory design as they present antenna designs. Along the way, questions about LPDA dimensions and performance kept arising to compound the design process--and to make more difficult the selection of a final LPDA design to build and test. In fact, some of the questions led to at least one non-LPDA alternative: a wide-band Yagi noted in Phase 6 of the process and further analyzed in Phase 7.
The job is not yet done, but I am in no hurry. What I am learning while designing
and deciding may turn out to be more important than the final product. As a matter
of fact, a fairly satisfactory design emerges in Phase 1. Then again, I never was
one to leave well enough alone.
Updated 11-21-98. © L. B. Cebik, W4RNL. Data may be used for
personal purposes, but may not be reproduced for publication in print or
any other medium without permission of the author.