Broad Band Atenna (Monopole or Helix)

[Behzadzahid]

I have to design broadband antenna for frequency range 25-110 MHz. Which antenna should i chose? Monopole, Helix, Dipole
and What should be the material ? copper etc

 

[flatulent]

Look into discone types.

 

[ferdows]

hi
which size u want to design ? its important and select the kind of your antenna

 

[enjunear]

I have to design broadband antenna for frequency range 25-110 MHz. Which antenna should i chose? Monopole, Helix, Dipole
and What should be the material ? copper etc

Monopoles are designed near λ/4 (one-quarter wavelength), so are narrowband by nature.

A helix is designed for the wire circumference near 1 wavelength, with a spacing of λ/4 between the coils... again, narrowband.

A dipole is generally designed at λ/2, again, narrowband.

For your design, you need a broadband antenna type. For most school antenna projects, the simplest broadband antenna design is an LPDA (Log-Periodic Dipole Array). There are many cookbook websites, and some with the real formulas to design and build one. It's pretty simple in practice. The longest element is approximately λ/2 long at the lowest frequency of interest (25 MHz), and the shortest element is λ/2 at the highest frequency of interest (110 MHz).

To quickly calculate the width of the antenna, use λ = c/f. So for 25 MHz, λ = 3e8 / 25e6 = 12 meters. For a half-wave dipole element, that'd be ~6m wide. For the high frequency, λ = 3e8 / 110e6 = 2.73 m, or 1.36 m wide fo the smallest element.

If this is for a class, there should be a design guide/walkthru/example for a simple LPDA antenna in your textbook. If not, find Antenna Theory by C.A. Balanis.... a VERY through text on this subject.

and yes, use copper. It's easy to work with (solderable, moderately soft) and a good conductor.