Thank you for visiting RF Cafe! 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 RF Cafe Homepage Thank you for visiting RF Cafe!

Decoupling and Coupling.. - 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

Post subject: decoupling and coupling.. Posted: Fri Apr 21, 2006 3:50 am


Joined: Sun Apr 09, 2006 8:48 pm
Posts: 2
Location: Penang
good day everybody,

Can anybody explanain definition of coupling and decoupling? what is their's purpose? how is their connection in RF matching circuit?



Post subject: Posted: Fri Apr 21, 2006 8:33 am

Site Admin

Joined: Mon Jun 27, 2005 2:02 pm
Posts: 373
Location: Germany
Hello ngks79,

AC or RF coupling is done with a series capacitor which its purpose is to deliver only the alternating or high frequency signal and block the DC in order not to vary the operating point of the active device (Usually transistor or amplifier). These series capacitors are often connected between a matching network and the input or output of the device. Their capacitance should be calculated in a way that their reactance is low in the lowest frequency of operation (not more than few ohms).

Decoupling means suppressing high frequency signals, this is usually done in supply voltages by connecting capacitors between the supply and GND rails. The capacitors short high-frequency signals (Interferers and noise) to GND.

Best regards,

- IR


Kirt Blattenberger
Post subject: Posted: Fri Apr 21, 2006 9:11 am

Site Admin

Joined: Sun Aug 03, 2003 2:02 pm
Posts: 308
Location: Erie, PA

A similar question was asked of me the other day at work on a related topic, and that was: What is the difference between a decoupling capacitor and a bypass capacitor? The questioner had been told by his college professor that a decoupling capacitor was used in series with an RF signal to block DC, and that a bypass capacitor was used on DC supply lines to shunt AC to ground.

IR's response is in line with my own usage of the term "coupling capacitor" for one used to pass RF and block DC. The terms "decoupling capacitor" and "bypass capacitor" are used interchangeably almost universally in technical literature and on all of the online electronics dictionaries (and app notes) I checked. Both terms describe a capacitor used to conduct AC to ground, or at least away from the signal path.

…just another data point.

- Kirt Blattenberger
RF Cafe Progenitor & Webmaster

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
Kirt Blattenberger,

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:

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