What capacitor to use to filter out 10GHz signal - RF Cafe Forums

The original RF Cafe Forums were shut down in late 2012 due to maintenance issues - primarily having to spend time purging garbage posts from the board. At some point I might start the RF Cafe Forums again if the phpBB software gets better at filtering spam.

Below are the old forum threads, including responses to the original posts.

-- Amateur Radio
-- Anecdotes, Gripes & Humor
-- Antennas
-- CAE, CAD, & Software
-- Circuits & Components
-- Employment & Interviews

-- Miscellany
-- Swap Shop
-- Systems
-- Test & Measurement
-- Webmaster

antennaant
Post subject: What capacitor to use to filter out 10GHz signal Posted: Mon Dec 11, 2006 3:20 pm

Lieutenant

Joined: Mon Dec 11, 2006 3:17 pm
Posts: 2
I have a 10GHz signal riding on all my DC inputs. I am thinking of using a low pass RC filter. But what kind of capacitor to use? Ceramic MLCC?

Top

fred47
Post subject: 10 GHz bypassPosted: Wed Dec 13, 2006 12:44 am

General

Joined: Wed Feb 22, 2006 3:51 pm
Posts: 104
Hi!

You say that you have "have a 10GHz signal riding on all my DC inputs".

A classic approach is to bypass the DC inputs, and use a resistor, inductor, or lossy ferrite to isolate the DC from the RF.

However, I'd like to caution you that one possible problem with an RC lowpass is the quality of the ground. At 10 GHz (wavelength about 3 cm), it doesn't take much distance to be an appreciable fraction of a wavelength. So, while a small MLC SMT capacitor would probably work, proper functioning would really almost more depend on the available ground path. As a rule of thumb, you should reach a ground plane within 1/10 of a wavelength, or 3mm. (And preferably less!)

Physical layout is increasingly critical as the frequency goes up.

Good Luck!

Fred

Top

sm7ovk
Post subject: Posted: Thu Jan 18, 2007 2:57 pm

Lieutenant

Joined: Thu Jan 11, 2007 12:59 pm
Posts: 4
Just wanted to mention that 10GHz easily can get outside an ordinary T-filter often used in digital circuits, as mentioned earlier the dimensions of the filters are often larger than 3mm. In a project some years ago I found feedthrough capacitors specified to 10GHz, think it was Murata but there are probably plenty of them out there - just be sure that they really are specified at least to the frequency you use or have problems with!

Regards
Jens

Top

yendori
Post subject: Posted: Thu Jan 18, 2007 5:52 pm

General

Joined: Thu Sep 25, 2003 1:19 am
Posts: 50
Location: texarcana
Check out Vishay. They have some pretty ok mos caps. I use them up to 10GHz.

Posted 11/12/2012

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 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: AirplanesAndRockets.com

My Daughter's Website: EquineKingdom

Innovative Power Products (IPP) RF Combiners / Dividers

Anatech Electronics RF Microwave Filters - RF Cafe