×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

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

spiral antenna gain

spiral antenna gain

spiral antenna gain

(OP)
How much more gain could I expect to get by placing a spiral above a reflecting cavity as opposed to a cavity backed spiral where the back lobe is absorbed?

RE: spiral antenna gain

It depends...

If the "reflecting cavity" was the 1000 foot diameter dish in Arecibo, then you could get quite a bit of gain...

If the "reflecting cavity" was badly designed, then you could have a deep null where you might normally expect to find gain.

RE: spiral antenna gain

(OP)
I was thinking in terms of a cavity 2 * dia, approx Lamda / 4 deep.

RE: spiral antenna gain

I'm not sure about the gain difference, however the patterns and operational bandwidth will change.  A spiral in a metal cavity will have an approximate octive bandwidth.  When the caity is loaded the bandwidth is greatly increased.  The max gain is typically acheived when the cavity is .25*lambda (wavelength).  Think in terms of an image (or dipole over a ground plane).


Reference: "Antenna Engineering Handbook" second edition by Johnson and Jasik, chapter 14.

RE: spiral antenna gain

(OP)
Thank you photistor, What gain would I expect from a spiral lamba/4 above a cavity as oposed to having an absorbing cavity. Would you expect a cavity to give 3 dB enhancement or 6 dB due to voltage squared being induced for doubling of power due to cavity?

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



News


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