passive Bessel filter?

[fonograph]

Is it possible to make passive 4th order bessel filter? I think I read somewhere that its impossible to make it from passive components,that it needd to be active filter in order to be bessel type,is that true?

[chris_leyson]

You can make a 4th order passive Bessel filter without any problems, to say it can only be done with active filters is nonsense.
You just have to find the right text book or the right software to design the filter. I think passive filter design is possable with Matlab or Octave which is free.

[Kalvin]

Is it possible to make passive 4th order bessel filter? I think I read somewhere that its impossible to make it from passive components,that it needd to be active filter in order to be bessel type,is that true?

Yes. False.

[fonograph]

Thank you,both of you.Is there any filter type that can only be active?

[Kalvin]

Ps. Here is a quick/short tutorial for designing passive filters using tables in a cookbook fashion:

http://web.stanford.edu/class/ee133/handouts/labs/EE133filterCookbook.pdf

[chris_leyson]

Is there any filter type that can only be active?

I can't think of any.

[basinstreetdesign]

Thank you,both of you.Is there any filter type that can only be active?

If you can classify a gyrator as a filter then there's that.

4th order Bessel?
Here's one pictured:

[LvW]

Thank you,both of you.Is there any filter type that can only be active?

Yes - all filters based on integrators are active because (nearly ideal) integrators can be realized only on the basis of active (amplifying) blocks.
Examples: KHN-Filter structure, Tow-Thomas.