RF filer design Matlab

2 views (last 30 days)
Michael Rojic
Michael Rojic on 12 Sep 2022
Commented: Star Strider on 15 Sep 2022
I am new to Matlab and RF Toolbox. I designed a Butterworth bandpass filter. Everything seemed to go OK, except I cannot see what the L & C values for the designed filter are. I can see S params and plots, but for this to really be a filter design tool, I need it to output the actual component values. ???

Answers (1)

Star Strider
Star Strider on 13 Sep 2022
I don’t have the RF Toolbox (since I don’t need it, although earlier as a U.S. Amateur Extra Class Amateur Radio operator, it would likely have been useful) however your question interested me enough to go searching.
The example in the rffilter documentation gives the component values, however you have to ask for them —
Using an example from the documentation —
robj = rffilter('ResponseType','Bandpass','Implementation','LC Tee','PassbandFrequency',[950e6 2200e6], ...
'StopbandFrequency',[770e6 3000e6],'PassbandAttenuation',3,'StopbandAttenuation',40);
robj.Name = 'BFCG_162W'
robj =
rffilter: Filter element FilterType: 'Butterworth' ResponseType: 'Bandpass' Implementation: 'LC Tee' PassbandFrequency: [950000000 2.2000e+09] PassbandAttenuation: 3 StopbandFrequency: [770000000 3.0000e+09] StopbandAttenuation: 40 Zin: 50 Zout: 50 DesignData: [1×1 struct] UseFilterOrder: 0 Name: 'BFCG_162W' NumPorts: 2 Terminals: {'p1+' 'p2+' 'p1-' 'p2-'}
lcladder(robj)
ans =
lcladder: LC Ladder element Topology: 'bandpasstee' Inductances: [1.8116e-09 5.7297e-09 8.3361e-09 2.8294e-09 1.2214e-08 2.3802e-09 1.2214e-08 2.8294e-09 8.3361e-09 5.7297e-09 1.8116e-09] Capacitances: [6.6900e-12 2.1152e-12 1.4539e-12 4.2835e-12 9.9228e-13 5.0919e-12 9.9228e-13 4.2835e-12 1.4539e-12 2.1152e-12 6.6900e-12] Name: 'lcfilt' NumPorts: 2 Terminals: {'p1+' 'p2+' 'p1-' 'p2-'}
The lcladder function produces them. There might also be other appropriate functions. See the Functions link for a list of all of them.
.
  4 Comments
Star Strider
Star Strider on 15 Sep 2022
My pleasure!
From the lcladder documentation:
it appears to be these in series. Other than this, I can’t find any schematics in the onlline documentation. (If you found others, please share the links.)
format shortE
robj = rffilter('ResponseType','Bandpass','Implementation','LC Tee','PassbandFrequency',[950e6 2200e6], ...
'StopbandFrequency',[770e6 3000e6],'PassbandAttenuation',3,'StopbandAttenuation',40);
robj.Name = 'BFCG_162W';
lclobj = lcladder(robj);
L = lclobj.Inductances
L = 1×11
1.0e+00 * 1.8116e-09 5.7297e-09 8.3361e-09 2.8294e-09 1.2214e-08 2.3802e-09 1.2214e-08 2.8294e-09 8.3361e-09 5.7297e-09 1.8116e-09
C = lclobj.Capacitances
C = 1×11
1.0e+00 * 6.6900e-12 2.1152e-12 1.4539e-12 4.2835e-12 9.9228e-13 5.0919e-12 9.9228e-13 4.2835e-12 1.4539e-12 2.1152e-12 6.6900e-12
There are equal number of ‘L’ and ‘C’ elements. I can find nothing in the documentation that describes the topology of the input and output ports of the lcladder object, however it may not matter if the series inductor or parallel capacitor are the first (or last) element in the circuit. There are some GUI apps the may depict the topolgy, however I don’t have access to them and the can’t be used online here. Since you have to RF Toolbox (I don’t), you will need to explore these.
.

Sign in to comment.

Tags

Products

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!