Post subject: High / RF filter design
Wed Feb 18, 2004 9:02 am
can anyione help
im trying to design a filter to accept 900mega hz to 1200 mega hz and
scan inbetween to pic up a specific signal.
i have been looking at
bandpass filters but working it out the componets come out at rediculouse
i have seen butters filters etc but i need some advice
as this area is very new to me and ive been thrown in at the deep end.
i need to be able to show worked out calculations (so i can understand
it) and have a circuit design.
can any one help?? please any
little thing even any other sites to reserch as im running short!
please email me direct with any info
Post subject: Some help
Unread postPosted: Wed Feb 18, 2004 4:10 pm
should have a design software to design filters. Nowadays engineers
almost never use numaclatures or tables to design filters (well only
the oldies, and I am not one of them :D ). One professional tool I recommend
is Eagleware with the most used common filters. There you can synthesize
your desired filter based on a given set of parameters as: Topology,
number of poles, cutoff frequencies, insertion loss etc. after the initial
values of synthesis based on the polynom of required topology, you will
fine tune the values until you get the desired filter's shape.
If you want some theoretical help you can begin the analysis from
the basic LPF filter (Prototype Filter), where based on the impedance
of generator and other parameters you can derive any kind of other filter
with the required parameters based on your requirements.
that in RFCAfe there was an article a couple of months ago regarding
butterworth and chebuchev filters. scroll back and you will find it.
I hope this helps,
Unread postPosted: Fri Mar 05, 2004 1:06 am
Agreed. The fastest way is to use Eagleware and refer to Randall
Rhea's book on HF filter design. The other common reference's (Zverev
etal.) will take far longer to comprehend and apply, although they are
more general and comprehensive in nature.
You can probably find
lumped element filter design software on the web.
Things to consider
is this a lumped or cavity design?
your values are probably
off because of the internal impedance of your filter, remember that
it can be adjusted and then use a transformer at the input and output
(commonly a plain old inductor or capacitor)
if your design is
lumped then do not pick an architecture with "floating" inductors if
possible. always keep one end terminated to ground if you can because
of parasitics. capacitors are generally more ideal in their performance
don't expect the software to give you a functioning filter at turn
on. almost all filters all require tuning and value adjustments to make
them work. it's a bit of an artform to tune a filter so I suggest that
if you know someone who's done it before, go find them
Fri Mar 05, 2004 1:10 am
Here's a good page:
Post subject: Pay attention to the
effect of the traces in the design
Unread postPosted: Fri Mar 05,
2004 10:57 am
One more thing to remember is the effect of the
traces on the design, meaning after you arrive to the desired values
you will have to connect between the componenets with 50 ohm microstrip
lines. They have an influence on the overall filter performance: They
add insertion loss. In addition the vias to the GND add inductance and
the substrate itself add capacitance.
You should define the substrate
in the simulation tool you are using: Dielectric coefficient, Loss Tangent,
Width of the substrate etc, and then add the length and shapes of your
traces to the design. It will simulate the reality in the best way.
Pay attention to the effect of the traces in the design
Fri Mar 05, 2004 8:56 pm
Welcome to forum!
First of all,
I need to know what is your applications, desired power level, rejection
requirements, vswr and insertion loss (i.e. full electrical specs).
Can you share? I'm sorry can not guess! Secondly, some people may get
you confused when it comes to LC or cavity filters. Cavity filter design
can be lumped and non-lumped element. It all depends on what is for
(we design them everyday). Is your filter for an experimental purpose?
You didn't make any inquiry, but I am taking the liberty to ask you.
Are you looking to buy? We are not cheap, but pretty good RF & MW
filtering products. It appears that you will need a BP Filter and you
can design it. But, keep in mind no filter is good for use until tuned,
tested and worked as expected. There are several books in market (you
can find them on web sites as well) to study (not only reading) to get
a basic understand of electrical, electronics, rf & microwave and
mechanical disciplines before get to software. Software design tools
program are good for advanced professionals. But, in your case you will
need foundation first.
Your questions, comments and answers are