Electronics World articles Popular Electronics articles QST articles Radio & TV News articles Radio-Craft articles Radio-Electronics articles Short Wave Craft articles Wireless World articles Google Search of RF Cafe website Sitemap Electronics Equations Mathematics Equations Equations physics Manufacturers & distributors Engineer Jobs LinkedIn Crosswords Engineering Humor Kirt's Cogitations RF Engineering Quizzes Notable Quotes Calculators Education Engineering Magazine Articles Engineering software RF Cafe Archives RF Cascade Workbook 2018 RF Symbols for Visio - Word Advertising RF Cafe Forums Magazine Sponsor RF Cafe RF Electronics Symbols for Visio RF Electronics Symbols for Office Word RF Electronics Stencils for Visio Sponsor Links Saturday Evening Post NEETS EW Radar Handbook Microwave Museum About RF Cafe Aegis Power Systems Anritsu Alliance Test Equipment Amplifier Solutions Anatech Electronics Axiom Test Equipment Berkeley Nucleonics Bittele Centric RF Conduct RF Copper Mountain Technologies Empower RF everything RF Exodus Advanced Communications Innovative Power Products ISOTEC KR Filters Lotus Systems PCB Directory Rigol RF Superstore San Francisco Circuits Reactel RFCT TotalTemp Technologies Triad RF Systems Windfreak Technologies Withwave LadyBug Technologies Wireless Telecom Group Sponsorship Rates RF Cafe Software Resources Vintage Magazines Thank you for visiting RF Cafe!
everythingRF RF & Microwave Parts Database (h1) - RF Cafe

filter design question- RF Cafe Forums

RF Cafe Forums closed its virtual doors in 2010 mainly due to other social media platforms dominating public commenting venues. RF Cafe Forums began sometime around August of 2003 and was quite well-attended for many years. By 2010, Facebook and Twitter were overwhelmingly dominating online personal interaction, and RF Cafe Forums activity dropped off precipitously. Regardless, there are still lots of great posts in the archive that ware worth looking at. Below are the old forum threads, including responses to the original posts.

NOTICE: The original RF Cafe Forum is available again for reading, and the new RF Cafe Blog is an active board.

-- Amateur Radio

-- Anecdotes, Gripes, & Humor

-- Antennas

-- CAE, CAD, & Software

-- Circuits & Components

-- Employment & Interviews

-- Miscellany

-- Swap Shop

-- Systems

-- Test & Measurement

-- Webmaster


Post subject: filter design Posted: Mon Mar 05, 2007 2:52 pm


Joined: Thu Mar 01, 2007 3:45 pm

Posts: 1

Location: california

When designing an interdigital or a combline bandpass filter in stripline, I frequently have a S21 dip, about 0.5 to 0.8dB in magnitude, near either low side or high side of the passband. For example, if the passband is 900MHz to 1.3GHz, this dip may occur at around 990MHz or 1.22GHz. There is a corresponding S11 spike at the same frequencies. What causes this? Can anyone enlighten me on this? Thanks.



Post subject: Posted: Tue Mar 06, 2007 6:28 am


Joined: Fri Feb 17, 2006 12:07 pm

Posts: 218

Location: London UK

Hi fxl

This will always happen when using an ellyptic function or a Chebychev design, and it is due to internal resonant paths within the structure.

Butterworth Constant Phase types avoid this, but have a slower roll-off for the same number of elements.

The attenuation variation (S21) across the band for a Chebychev should never exceed the design ripple factor (eg. 0.25dB) by any more than the small margin for dissipation due to finite Q values of the elements. If you are looking for maximum stop band roll-off rate, choose ripple factor at say 1.0dB, and that will be the variation limit across the band.

Note also that the -3dB bandwidth and the equal ripple bandwidth are different from each other, which is warning you that between the ripple factor frequency and the -3dB frequency the S21 (and S11) will vary wildly. There is a formula relating them, but I will have to look for it.

Posted  11/12/2012

Exodus Advanced Communications Best in Class RF Amplifier SSPAs - RF Cafe
withwave microwave devices - RF Cafe
Anatech Electronics (RF Filters) - RF Cafe
Holzworth RF Synthesizers
Exodus Advanced Communications Best in Class RF Amplifier SSPAs

Please Support RF Cafe by purchasing my  ridiculously low−priced products, all of which I created.

These Are Available for Free


About RF Cafe

Kirt Blattenberger - RF Cafe Webmaster

Copyright: 1996 - 2024


    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 World Wide Web (Internet) was largely an unknown entity at the time and bandwidth was a scarce commodity. Dial-up modems blazed along at 14.4 kbps while tying up your telephone line, and a nice lady's voice announced "You've Got Mail" when a new message arrived...

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: