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!

Microstrip Impedance vs. Frequency - 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: Microstrip impedance vs. frequency Posted: Sun Sep 25, 2005 10:14 pm
two questions: 1) as the frequency increases what happens to microstrip characteristic impedance assuming dispersion affects are included?

2) i think at high freq., impedance will decrease....to compensate for it do i make width bigger or smaller? my understanding is that you have to increase the width to get higher impedance. answers will be much appreciated. thanx



Post subject: microstripPosted: Wed Sep 28, 2005 5:50 pm
I'm at work right now & don't have access to the papers - but Rogers Corp. has an on-line calculator (downloadable too) and the formulas it's based on in this pdf:


Good Luck!


Post subject: Posted: Wed Sep 28, 2005 7:05 pm
A microstrip transmission line will tend to
"roll off" as frequency increases.
This is because the shunt capacitance becomes

A 50 ohm line is a 50 ohm line regardless of frequency.


Post subject: microstripPosted: Thu Sep 29, 2005 2:26 pm
anormalhouse said: "A 50 ohm line is a 50 ohm line regardless of frequency".

Not true. Most substrate materials have a dielectric constant which is a function of frequency. Since the dielectric constant is part of the impedance formulas, the characteristic impedance varies with frequency.

FR4 is a particularly blatantly bad example of this. "50 Ohm lines" on FR-4 vary from 50 Ohms as the frequency goes above 1 GHz. This is in the literature. Again, see the Rogers website.

Good Luck!


Post subject: Posted: Thu Sep 29, 2005 2:40 pm
Yeah, you kinda missed my point.


Post subject: Posted: Thu Sep 29, 2005 4:26 pm

you guys really didn't answer the question and i'd like someone to answer it again for me also and for the person who orginally asked the question. taking into account frequency effects what will happen to impedance when the width is increased?


Post subject: Posted: Thu Sep 29, 2005 4:37 pm
whoa, whoa, calm down "guest". We'll aswer the questions in due time.

Let me have a cup of coffee first, then we can all about frequency vs. line width, dielectric constants, and dogs.


Post subject: Posted: Fri Sep 30, 2005 6:46 am
When you increase the width the impedance goes down, mor capacitive. Decreasing the width the impedance goes up, more inductive.

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 Chartâ„¢ for Visio
Smith Chartâ„¢ 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 !