yagi uda antenna

[Gaston]

dose anyone have any formulas so i can calculate a yagi antenna? i have been searching for an hour and cant come up with anything

 

[Russlk]

I did a Google search using "yagi antenna formula" and found lots of sites. Also, your library should be able to get an antenna book, I have the 1949 A. R. R. L. Antenna Book, Rumford Press, which is no doubt out of print, but may be available in the library.

 

[zevon8]

Antenna design can be considered and "art" as much as a science. First you start with what "it should be like" then experiment with it until it becomes that. A Yagi can be as simple as 3 peices of wire of the correct length, spaced to suit the frequency. It can also become a complex mess of reflectors and directors that looks like some crazy pile of ladders.

A classic simple 3 element Yagi looks like this: ( brace yourself for bad ASCII art )

I
I I
I I I
I I I
I I I
I I
I


The longest element on the left is 0.55( wavelength ), the middle ( which is in two equal pieces ) is 0.5 ( wavelength), the last is 0.45 ( wavelength) . The spacing between , left to right, is one tenth of the wavelength. The small end is the direction to point the antenna.

Wavelength is calculated by : L=v/f where L = wavelength, v=speed of light ( 300,000 m/s ) , f = frequency

giving, for say 100MHz, L= 300,000/100,000 or 3 meters.

Plugging this into the above, gives us this:

0.55(3)= 1.65 meters
0.5(3)= 1.5 meters
0.45(3)= 1.35 meters
spacing = 3/10 = 0.3 meters

Of course, this will result in a fairly poor antenna, due to the limited number of elements, one reflector, on driven element, and one director.

I think you would probably find that many designs for what you need to do already exist on the internet, especially things like the "can-tenna" made from a potato chip can, used on wireless routers.

What is the antenna to be used for? Narrowing it down will help greatly in deciding what type of design would be best for your needs.

 

[stevez]

Quite a few amateur radio publications address antenna design - ARRL (US) and RSGB (UK) are two organizations (radio amateurs) that you might look to for information. ARRL Antenna Handbook is still published every year. The ARRL website allows access to non-members for some periodicals - you may find a nice explanation there.

As suggested already it's kind of an art and science thing. The science is where you apply theory, engineering, math, etc. The art is in adapting the materials, methods and processes available to you in building the final product.

 

[Gaston]

could you use more than one reflector. and if you add more directors do you just keep decreaseing the length by the same rate?

 

[Nigel Goodwin]

could you use more than one reflector. and if you add more directors do you just keep decreaseing the length by the same rate?

What are you actually trying to do?, make an aerial for a specific frequency that you can't buy commercially?, or just try and improve your TV reception?.

 

[Gaston]

i am working on a school project. we have to make an antena for 440mhz and get a certain amount of gain out of it. i dont remember the amount of gain but i want to exceed the minumum. i know that the half wave dipole has to be a little shorter than a half wave. but do the directors and reflector have to be a little shorter also?

 

[zevon8]

The reflectors are generally little longer, the directors are generally shorter than driven element. You can add as many as you want, experimentation based on proven designs will tell you when you have reached a practical limit. Often there are way more directors than reflectors.

 

[Nigel Goodwin]

i am working on a school project. we have to make an antena for 440mhz and get a certain amount of gain out of it. i dont remember the amount of gain but i want to exceed the minumum. i know that the half wave dipole has to be a little shorter than a half wave. but do the directors and reflector have to be a little shorter also?

As already mentioned, there are loads of sites on the net, which a simple google will find. Plenty of these have calculators for desgning yagi's, just enter your specs and let them calculate it for you.

 

[stevez]

You might look closely at the 70 cm ham radio band for antennas. If you have some goals in mind you might compare your goals to what's described which will give you a place to start.

Some friends have analyzed existing proven designs to improve their design skills.