Electronics World Cover,TOC,and list of posted Popular Electronics articles QST Radio & TV News Radio-Craft Radio-Electronics Short Wave Craft Wireless World About RF Cafe RF Cafe Homepage RF Cafe in Morse Code Google Search of RF Cafe website Sitemap Electronics Equations Mathematics Equations Equations physics Manufacturers & distributors Engineer Jobs Twitter LinkedIn Crosswords Engineering Humor Kirt's Cogitations Engineering Event Calendar RF Engineering Quizzes AN/MPN-14 Radar 5CCG Notable Quotes App Notes Calculators Education Magazines Software,T-Shirts,Coffee Mugs Articles - submitted by RF Cafe visitors Simulators Technical Writings RF Cafe Archives Test Notes Wireless System Designer RF Stencils for Visio Shapes for Word Search RF Cafe Sitemap Advertising Facebook RF Cafe Forums Thank you for visiting RF Cafe!

Definition of dBi - RF Cafe Forums

The original RF Cafe Forums were shut down in late 2012 due to maintenance issues. Original posts:

Amateur Radio | Antennas | Circuits & Components | Systems | Test & Measurement


malvinas2
 Post subject: Definition of dBi
Posted: Fri Aug 26, 2005 3:23 am 
You can find some tutorials about antennas on Kirts Website:

decibels relative to isotropic radiator

The expression dBi is used to define the gain of an antenna system relative to an isotropic radiator at radio frequencies. The symbol is an abbreviation for "decibels relative to isotropic."

The dBi specification is based on the decibel, a logarithmic measure of relative power. Suppose an antenna A produces an electromagnetic field of intensity IA microwatts per square meter (IAµW/m2) in its favored direction at a point located some distance away. Also, suppose an isotropic antenna Q produces an electromagnetic field of intensity IQ µW/m2 at the same distance. Then the gain G of antenna A, in dBi, is:

G = 10 log10 (IA / IQ)

A dipole antenna has a gain of 2.15 dBi. An isotropic radiator has a gain of 0 dBi.

Note: In real life an isotropic radiator doesn't exist, it's just an idea.


 
  
 
Graham
 Post subject:
Posted: Sun Sep 04, 2005 7:40 pm 
 
Colonel
User avatar

Joined: Fri Sep 02, 2005 7:25 pm
Posts: 34
Location: Hampshire UK
Expanding on that a bit, the notion of a mathematiaclly "pure" isotropic radiation point source has, for the antenna manufacturers the agreeable effect of allowing them to add 2.15dB to their gain figures.

In practice, you can only measure the gain of the antenna relative to a known reference antenna - this being a dipole which can be made accurately and repeatably. The test environment either eliminates or accounts for ground or other surfaces contributing (reflection gain). Then you add the 2.15 dB to turn dBd into dBi






Posted  11/12/2012

RF Cafe Software

   Wireless System Designer - RF Cafe
Wireless System Designer

RF & EE Symbols Word
RF Stencils for Visio
Calculator Workbook
RF Workbench
Smith Chart™ for Visio
Smith Chart™ for Excel

About RF Cafe

Kirt Blattenberger - RF Cafe WebmasterCopyright
1996 - 2022
Webmaster:
Kirt Blattenberger,
 BSEE - KB3UON

RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling 2 MB. Its primary purpose was to provide me with ready access to commonly needed formulas and reference material while performing my work as an RF system and circuit design engineer. The Internet was still largely an unknown entity at the time and not much was available in the form of WYSIWYG ...

All trademarks, copyrights, patents, and other rights of ownership to images and text used on the RF Cafe website are hereby acknowledged.

My Hobby Website:
 AirplanesAndRockets.com

Try Using SEARCH
to Find What You Need. 
There are 1,000s of Pages Indexed on RF Cafe !

height-line