Is it possible to determine coefficients of an analog Bessel filter based on order, fc and attenuation only?
Is it possible to obtain the filter coefficients based on such limited info?


In principle yes.


it is a Low-pass filter
it has a cut-off frequency of 2 kHz
roll-off is 80 dB/decade so that means it is a (4 x 20 dB/decade) 4th order filter
since no input and output impedance are given, I will assume both are 50 ohms


The "oldfashioned" way to design such a filter was to lookup the coefficients in a book like Zverev, do some "magic" with those numbers and you'd have your filter design.

Luckily there are easier methods these days. I prefer to use QUCS (it is free software!) which is a circuit simulator (so you can immediately simulate your filter!) but it has a built-in filter generator which I use quite often.

So I filled in the above specifications and then I get:



As stated, this filter requires the 50 ohm input and output impedances. If you want something different and since you're making a model it is quite easy to use controlled sources (voltage to voltage, current to voltage, etc) to make the impedances as seen from "outside" as you need them without affecting the filter.

For example, if you replace P1 a voltage to voltage source in series with 50 ohms, like this:







simulate this circuit &ndash; Schematic created using CircuitLab

then you get a high impedance input but the filter still sees a 50 ohm source (which it needs).