Copyright: 1996 - 2024
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 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:
Filter design - RF Cafe Forums
RF Cafe Forums closed its virtual doors in 2012 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. If the folks at
phpBB would release a version with integrated
sign-in from the major social media platforms, I would resurrect the RF Cafe Forums,
but until then it is probably not worth the effort. 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.
|-- Amateur Radio
Gripes & Humor
-- CAE, CAD, &
Test & Measurement
Post subject: Filter design
Unread postPosted: Sun Mar
20, 2005 8:25 pm
I have one doubt regarding filter
design for mobile phones, commonly it can be done by shebyshev design,
however is it possible to do by microstrip filter design? Am I right
to say that the difference between those 2 is chebyshev design using
lumped components? :?:
and I guess that the microstrip filters
are better using for this condition, especially at high frequency operation?
Looking forward for your advice.
Thank you for enlighten
Unread postPosted: Sat Mar 26, 2005 9:32 am
A microstrip filter is perfectly possilbe at 900 MHz, but it is
not used in mobile phones because it would be very large. There are
techniques for miniturising
microstrip filters, but it would still
be impractical for handset use.
The filters used in mobile phone
handsets are generally coupled ceramic resonators or SAWs, which are
cheap, small and have relatively good selectivity.
filters are designed using the same prototypes (chebyshev, butterworth
etc) as lumped element designs. The Richards transform is used to translate
lumped elements into lines.
If you have interest in this area,
I recommend the following books:
Microwave Engineering - DM Pozar
Microstrip Filters - Hong & Lancaster ISBN 0471388777
Mon Mar 28, 2005 1:23 am
Thank you for your advice and suggestions.
Unread postPosted: Mon Mar 28, 2005 4:11 am
Any topology that
can be used for lumped elements can be used for microstrip elements,
the difference is only in the implementation. Microstrip filters are
indeed too big for using them in mobile handsets, but they are often
used in RF boards for cellular/GSM frequncies.