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UWB Bandpass Filter Using Open and Short-Circuited Stubs

This example shows how to create an open or short circuited stub filter using the filterStub catalog and analyze the filter using RF PCB Toolbox.

UWB 5-Pole Short Circuited Bandpass Filter

Schematic

Create filter

Use the filterStub object to create a stub filter. Define port lines and series line using the properties of PortLineLength, PortLineWidth, SeriesLineLength, and SeriesLineWidth. Define the stub length, stub width, and stub position using StubLength, StubWidth, and StubOffsetX. Set the StubShort and StubDirection according to the structure.

filter1 = filterStub;
filter1.PortLineLength = 5.4e-3;
filter1.PortLineWidth = 1.3e-3;
filter1.SeriesLineLength = 18.7e-3;
filter1.SeriesLineWidth = 0.1e-3;
filter1.StubLength = [7.1e-3 1.65e-3 1.65e-3 1.65e-3 1.65e-3 8.8e-3 1.65e-3 1.65e-3 1.65e-3 1.65e-3 7.1e-3];
filter1.StubWidth = [0.8e-3 1.6e-3 1.6e-3 1.6e-3 1.6e-3 1.7e-3 1.6e-3 1.6e-3 1.6e-3 1.6e-3 0.8e-3];
filter1.StubOffsetX = [-9.35e-3 -6.95e-3 -6.95e-3 -2.85e-3 -2.85e-3 0e-3 2.85e-3 2.85e-3 6.95e-3 6.95e-3 9.35e-3];
filter1.StubShort = [1 0 0 0 0 1 0 0 0 0 1];
filter1.StubDirection= [0 1 0 1 0 0 1 0 1 0 0];
filter1.GroundPlaneWidth= 0.0220;
filter1.Height = 0.508e-3;
substrate = dielectric("EpsilonR",3.05,"LossTangent",0.0001,"Thickness",0.508e-3);
filter1.Substrate = substrate;

Visualize stub filter

Use the show function to visualize the filter.

figure;show(filter1)

Figure contains an axes object. The axes object with title filterStub element contains 9 objects of type patch, surface. These objects represent PEC, feed, Air.

Analyze filter

Use the mesh function and assign the MaxEdgeLength to 10 mm to ensure 25 triangles per wavelength.

figure;mesh(filter1,"MaxEdgeLength",0.010)

{"String":"Figure contains an axes object and an object of type uicontrol. The axes object with title Metal-Dielectric contains 1269 objects of type patch, surface. These objects represent PEC, feed, Air.","Tex":"Metal-Dielectric","LaTex":[]}

Use the sparameters function to calculate the S-Parameters and plot it using rfplot function.

s1=sparameters(filter1,linspace(1e9,15e9,101));
figure;rfplot(s1);

Figure contains an axes object. The axes object contains 4 objects of type line. These objects represent dB(S_{11}), dB(S_{21}), dB(S_{12}), dB(S_{22}).

UWB 9-Pole Short Circuited Bandpass Filter

Schematic

Create filter

Use the filterStub object to create a stub filter. Define port lines and series line using the properties of PortLineLength, PortLineWidth, SeriesLineLength, and SeriesLineWidth. Define the stub length, stub width, and stub position using StubLength, StubWidth, and StubOffsetX. Set the StubShort and StubDirection according to the structure.

filter2 = filterStub;
filter2.PortLineLength = 0.01;
filter2.PortLineWidth = 1.3e-3;
filter2.SeriesLineLength = [14.075e-3 14.1e-3 14.1e-3 14.075e-3];
filter2.SeriesLineWidth = [1.2e-3 1.15e-3 1.15e-3 1.2e-3];
filter2.StubLength = [7.75e-3 7.55e-3 7.575e-3 7.55e-3 7.75e-3];
filter2.StubWidth = [0.6e-3 1.25e-3 1.45e-3 1.25e-3 0.6e-3];
filter2.StubOffsetX = [-28.175e-3 -14.1e-3 0 14.1e-3 28.175e-3];
filter2.StubShort = ones(1,5);
filter2.StubDirection= zeros(1,5);
filter2.GroundPlaneWidth= 0.0220;
filter2.Height = 0.508e-3;
substrate = dielectric("EpsilonR",3.05,"LossTangent",0.0001,"Thickness",0.508e-3);
filter2.Substrate = substrate;

Visualize stub filter

figure;show(filter2)

Figure contains an axes object. The axes object with title filterStub element contains 11 objects of type patch, surface. These objects represent PEC, feed, Air.

Analyze the filter

Use the mesh function and assign the MaxEdgeLength to 10 mm ensure 25 triangles per wavelength.

figure;mesh(filter2,"MaxEdgeLength",0.02)

{"String":"Figure contains an axes object and an object of type uicontrol. The axes object with title Metal-Dielectric contains 1401 objects of type patch, surface. These objects represent PEC, feed, Air.","Tex":"Metal-Dielectric","LaTex":[]}

Use the sparameters function to calculate the S-Parameters and plot it using rfplot function.

s2=sparameters(filter2,linspace(1e9,15e9,101));
figure;rfplot(s2);

Figure contains an axes object. The axes object contains 4 objects of type line. These objects represent dB(S_{11}), dB(S_{21}), dB(S_{12}), dB(S_{22}).