Filter design - RF Cafe Forums
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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.