Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Distance between two arms of dipole

Distance between two arms of dipole

Distance between two arms of dipole

I know this is a very trivial question, but I will ask it just for interest's sake.

What should be the distance between the feedpoints of the two arms of a dipole antenna? Is it related to the frequency? Or does it even matter?

How about monopoles?

Thanks in advance!

Operation Radiation: http://www.mrkenneth.com

RE: Distance between two arms of dipole

If you are talking about a standard run-of-the-mill halfwave doublet, the center should be relatively close together IM (not so) HO.  There is an EMF minimum at the center of a .5 Lambda antenna and a current maxima.  This holds true whether the antenna is center fed (Voltage Feed)or end fed or Zepp fed (Current Feed).

Now, if you are talking about a two half waves in phase (colinear) antenna, there is an advantage to just having the antenna apetures touch at the center.  In the case of a wire antenna, the optimal spacing is on the order of .25 Lambda.  An Extended Double Zepp (EDZ) antenna operates as a colinear.  The EDZ is a doublet .64 Lambda per side.  The inner .14 Lambda acts as an extension of the transmission line widening the spacing between the colinear elements for a slightly higher gain.

So, since there is maximum current and minimum porential at the center of a halfwave doublet, there is less possibility for arcing across the center insulator, therefore closer spacing of the elements is possible.

Whatever your project, may it come out well.

I remain,

The Old Soldering Gunslinger

RE: Distance between two arms of dipole

Wow! Thank you for the detailed explanation! So many new terms there!

I ask the question out of curiosity, because I have read anything that addresses the question.

For a typical centre-fed half-wave doublet, should the feedpoints be as close as possible? What factors does the distance between the two arms of the antenna affect?

Should the dipole be 0.5 wavelengths long including or excluding the empty space between the two arms of the dipole?

How about the distance between the wire of a monopole and the groundplane?

Thanks in advance!

Operation Radiation: http://www.mrkenneth.com

RE: Distance between two arms of dipole

Thank you VE1BLL for the wonderful link!

Now I have some ready to do. :)

Operation Radiation: http://www.mrkenneth.com

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close