need help on yagi antenna
I'm writing a project on the analysis of a yagi antenna using method of moments.
having searched the web, i found all sorts of yagi antenna. some with uniform spacing and some with varying spacing. Please, is there any formula guiding the spacing in a yagi antenna and how does this affect the functionality of the yagi antenna.
Also i'll need a reference for method of moments.
Thanks
The arrangements of the reflector and directors elements side by side of the driven element give the antenna directionality.
I don?t think is any right "one formula" to do this correctly because everything in antenna design is interactive. So, changing one dimension per a formula results in the need to change other dimensions or parameters.
Instead of formulas, the antenna design programs use interactive algorithms that automatically make all the other changes properly, if you change one thing.
The best optimization for a Yagi antenna you can find only using computer softwares.
Different directivities, gains, front-to-back ratios, side lobs, etc, arrives to different spacing between elements.
Thanks vfone for ur reply.
I'll appreciate if you can post any comprehensive book or document on method of moments.
my e-mail address is segun_oyetunji@yahoo.com
segun
yes there is formulas concern the spaces and the length of the dipoles of yagi antennas , depends to the gain the directivity and the frequency, these formulas u can find it easely in any antennas book, for example u can find it in: antenna Theory and design (Stutzman) Ch 5
reference for method of moments is in link:
http://rapidshare.com/files/21455793...ngton.rar.html
There is more stuff on this site than you could ever need on yagi-uda antennas. Just use the search function for "yagi". There are at least five pages of threads on the subject.
One criteria for yagi-udi antennas is the bandwidth. If you are maximizing gain the bandwidth is a few percent. During the 1939-1945 war there was a design for the military that had a 40% bandwidth but 3 dB lower gain.
Other criteria are front to back ratio and sidelobe levels.
Each one of these has a different set of element lengths and element spacings.
The diameter of the boom (if it is metal) has a strong effect on the calculations.
In the VHF range just a one inch difference from a given design is enough to totally ruin the performance.
thank you all.
i really got a great deal of help from the links.
:D