×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Are you an
Engineering professional?
Join Eng-Tips Forums!
• Talk With Other Members
• Be Notified Of Responses
• Keyword Search
Favorite Forums
• Automated Signatures
• 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.

# Antenna dBi issue.

 Forum Search FAQs Links MVPs

## Antenna dBi issue.

(OP)
Hi, it's my first time on the website.

I know how an isotropic antenna works. I work in the certification business and I keep seeing 0 dBi gain antennas. (Whip, Beamwidth 360 horizontal and 45 vertical.) Is this possible? I thought it was:
Beamwidth:
H, 360
V, 90
Gain = 3 dBi

Beamwidth:
H, 360
V, 360
Gain = 0 dBi

### RE: Antenna dBi issue.

Looks right,
for an omni antenna like a perfect dipole, the gain formula is 112/Beamwidth (-3 dB rolloff angle in degrees).

There are many simple formulas out there for gain based on the angle in degrees at the -3 dB rolloff in power (relative to peak).

dBi is decibels relative to isotropic.
bel = Alexander Graham Bell who first plotted in log base 10.
deci is 10xlogbase10(power), seems other scientists thought multiplying by 10 was easier to read.

Common alternate units for dB() are;
dBiC (C=circuilar polarization),
dBiL (L=linear polarization),
dBiD (D=dipole, which has 2.1 dBi gain, so if you have 5 dBiD gain, it's actually 5+2.1=7.1 dBi or dBiL gain).

dBi really needs something else added to it for completeness, either the word linear, circular(Right hand or left hand) or dBiD (which is always linear).

### RE: Antenna dBi issue.

I'm guessing that those formulas actually calculate directivity, where

gain = (antenna efficiency) * (directivity)

For instance, if based on beamwidth, you expect an antenna to have 3 dBi of directivity, but the manufacturer advertises the gain to be 0 dBi, that would imply the antenna efficiency is 50%.

Peter

### RE: Antenna dBi issue.

As Peter wrote, loss is the simplest explanation for the apparent anomaly in the 0 dBi gain and non-spherical coverage pattern beamwidth figures.

#### 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.

#### 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

#### Resources

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 partâ€™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:

• Talk To Other Members
• Notification Of Responses To Questions
• Favorite Forums One Click Access
• Keyword Search Of All Posts, And More...

Register now while it's still free!