[SI-LIST] Re: ask for comments on high frequency filter design

Wei,

For a filter much above 1 GHz I would be thinking of a distributed =
implementation as the elements start to become of practical size. I have =
tried using Inductors and Capacitors over 1 GHz before but its very =
difficult to model the effect of strays - you end up just building a =
very rough cut and then tweeking for ages. With the distributed type you =
can use the many handbook methods and equations knocking around to get a =
rough cut of what you need then go to a EM simulator such as sonnet to =
confirm and tweek your cut a bit.

You really need to understand the design spec your trying to meed before =
you can proceed. Such things as the power handling of the filter, its =
physical size limits, operating temperature range and tolerances are =
often overlooked. Of course the standard stuff like the ammount of =
insertion loss you can tolerate, the ammount of stopband attenuation you =
need, the bandwidth etc etc are also of utmost importance. You really =
need to work the destination before you begin the journey! You may find =
that the way you must build the filter is very quickly narrowed down =
once you put a spec on it!!

There are literally thousands of books on filter design, but if it was =
me in your shoes I would have a look for some information from those who =
make their money from filters such as K & L Etc. See how they do things. =
I am pretty sure they tend to use modified coaxial structures which =
include series capacitances within the coaxial. In this way they are =
able to implement distributed elements withn a coax

Have fun

steve

Steve Rogers B.Eng (Hons) C.Eng IEE
RF Design Engineer

Micromill Electronics Limited
Leydene House
Waterberry Drive=20
Waterlooville Hampshire
PO7 7XX

Tel: +44 (0) 23 9236 6600
Fax: +44 (0) 23 9236 6673

Registered No. 1456922 (England). =20
Registered Office Brook Road
Wimborne, Dorset BH21 2BJ

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-----Original Message-----
From: Wei Zhang [mailto:wezhang@xxxxxxxxxxxxxxx]
Sent: Tuesday, March 25, 2003 8:46 PM
To: si-list@xxxxxxxxxxxxx; circuits@xxxxxxxxxxxxx
Subject: [SI-LIST] ask for comments on high frequency filter design=20





Hi,

I need some professional comments on filter design, does anyone tell me
what is the major method applied to design a high frequency filter, say
center f between 1GHz and 10 GHz. As I read Reinhold Ludwig's "Rf =
circuit
design", he explains the methodolgy of filter design as receipe-cooking,
all kinds of filters can be implemented based on basic lowpass filter,
such as Butterworth, Chebyshev filter, with frequency and L/C
transformation. Furthermore, we can use unit elements and Kuroda's
identities to implement RF filter design. Is this a real practical =
method
in RF circuit design? If not, which one do you use? Can you give me some
detail information?               =20

Thanks for your help!

wei zhang


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