|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 me..
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.
Microstrip 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 ISBN 0471170968
Microstrip Filters - Hong & Lancaster ISBN 0471388777
Unread postPosted: 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.