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coupledStripLine

Create coupled transmission line in stripline form

Since R2024a

Description

Use the coupledStripLine object to create an edge-coupled differential pair transmission line in a stripline form. Coupled striplines are used to connect RF components, such as directional couplers, within the inner layers of a PCB board.

For the electromagnetic (EM) interactions between the ground planes, the feeds are located on the centers of the strips' edges at the board boundary and are simultaneously excited against both ground planes.

Types and applications of coupled stripline transmission lines:

Creation

Description

sline = coupledStripLine creates a default coupled transmission line in the stripline form. The default properties are for a resonant frequency of 2.5 GHz along the X-Y plane.

example

sline = coupledStripLine(name=value) sets properties using one or more name value pair arguments. For example, sline = coupledStripLine('Length',0.0300) creates a coupled stripline of length 0.0300 meters. Properties not specified retain their default values.

example

Properties

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Length of the coupled stripline in meters, specified as a positive scalar.

Example: strip = coupledStripLine('Length',0.0300)

Data Types: double

Width of the coupled stripline in meters, specified as a positive scalar.

Example: strip = coupledStripLine('Width',0.0037)

Data Types: double

Spacing between the coupled lines in meters, specified as a positive scalar.

Example: strip = coupledStripLine('Spacing',0.00037)

Data Types: double

Height from the ground plane to the coupled stripline in meters, specified as a positive scalar.

Example: strip = coupledStripLine('Height',9.000e-04)

Data Types: double

Width of the ground plane in meters, specified as a positive scalar.

Example: strip = coupledStripLine('GroundPlaneWidth',0.0350)

Data Types: double

Type of dielectric material used as a substrate, specified as a dielectric object. For more information see dielectric. The default dielectric material Teflon has an EpsilonR of 2.2, loss tangent of 0.03, and a thickness of 0.0032.

Example: d = dielectric('FR4'); strip = coupledStripLine('Substrate',d)

Data Types: string | char

Type of metal used for the conducting layers, specified as a metal object. For more information see metal.

Example: m = metal('PEC'); strip = coupledStripLine('Conductor',m)

Data Types: string | char

Object Functions

chargeCalculate and plot charge distribution
currentCalculate and plot current distribution
designDesign symmetric coupled stripline transmission line around given frequency
feedCurrentCalculate current at feed port
getZ0Calculate characteristic impedance of transmission line
meshChange and view mesh properties of metal or dielectric in PCB component
showDisplay PCB component structure or PCB shape
sparametersCalculate S-parameters for RF PCB objects
layoutPlot all metal layers and board shape
shapesExtract all metal layer shapes of PCB component
rlgcCompute resistances, inductances, conductances, and capacitances
getZEvenCalculate even mode impedance of differential PCB transmission line
getZOddCalculate odd mode impedance of differential PCB transmission line
propagationDelayCompute propagation delay of transmission line
dgsCreate defected ground structure of PCB element

Examples

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Create and view a default coupled strip line.

strip = coupledStripLine
strip = 
  coupledStripLine with properties:

              Length: 0.0202
               Width: 0.0026
             Spacing: 9.7000e-04
              Height: 0.0016
    GroundPlaneWidth: 0.0156
           Substrate: [1×1 dielectric]
           Conductor: [1×1 metal]

show(strip)

Figure contains an axes object. The axes object with title coupledStripLine element, xlabel x (mm), ylabel y (mm) contains 10 objects of type patch, surface. These objects represent PEC, feed, Teflon.

Create and view a coupled strip line at the interface of a multi-layered dielectric.

sub = dielectric('FR4','Teflon');
sub.Thickness = [0.003 0.001];
coupledstripline = coupledStripLine('Height',0.003,'Substrate',sub);
show(coupledstripline);

Figure contains an axes object. The axes object with title coupledStripLine element, xlabel x (mm), ylabel y (mm) contains 10 objects of type patch, surface. These objects represent PEC, feed, FR4, Teflon.

Plot the charge and current distribution on this transmission line.

current(coupledstripline,2.5e9)

Figure contains an axes object. The axes object with title Current distribution, xlabel x (m), ylabel y (m) contains 5 objects of type patch.

figure;
charge(coupledstripline,2.5e9)

Figure contains an axes object. The axes object with title Charge distribution, xlabel x (m), ylabel y (m) contains 5 objects of type patch.

Create and show a symmetric coupled transmission line

freq = linspace(1e9, 5e9, 41);
s1 = coupledStripLine;
s1
s1 = 
  coupledStripLine with properties:

              Length: 0.0207
               Width: 0.0051
             Spacing: 0.0019
              Height: 0.0030
    GroundPlaneWidth: 0.0241
           Substrate: [1x1 dielectric]
           Conductor: [1x1 metal]

figure; show(s1);
title('Symmetric coupled stripline');

Figure contains an axes object. The axes object with title Symmetric coupled stripline, xlabel x (mm), ylabel y (mm) contains 10 objects of type patch, surface. These objects represent PEC, feed, Teflon.

sp1 = sparameters(s1, freq);
figure; rfplot(sp1, 1:4, 1);
title('Symmetric coupled stripline');

Figure contains an axes object. The axes object with title Symmetric coupled stripline, xlabel Frequency (GHz), ylabel Magnitude (dB) contains 4 objects of type line. These objects represent dB(S_{11}), dB(S_{21}), dB(S_{31}), dB(S_{41}).

Create, and show an asymmetric coupled stripline transmission line

freq = linspace(1e9, 5e9, 41);
s2 = coupledStripLine;
s2
s2 = 
  coupledStripLine with properties:

              Length: 0.0207
               Width: 0.0051
             Spacing: 0.0019
              Height: 0.0030
    GroundPlaneWidth: 0.0241
           Substrate: [1x1 dielectric]
           Conductor: [1x1 metal]

s2.Substrate.Name        = {'Teflon', 'Teflon'};
s2.Substrate.EpsilonR    = [2.1        2.1];
s2.Substrate.LossTangent = [2e-4       2e-4];
s2.Substrate.Thickness   = [s2.Height  s2.Height/2];
figure; show(s2);
title('Asymmetric coupled stripline');

Figure contains an axes object. The axes object with title Asymmetric coupled stripline, xlabel x (mm), ylabel y (mm) contains 10 objects of type patch, surface. These objects represent PEC, feed, Teflon.

sp2 = sparameters(s2, freq);
figure; rfplot(sp2, 1:4, 1)
title('Asymmetric coupled stripline');

Figure contains an axes object. The axes object with title Asymmetric coupled stripline, xlabel Frequency (GHz), ylabel Magnitude (dB) contains 4 objects of type line. These objects represent dB(S_{11}), dB(S_{21}), dB(S_{31}), dB(S_{41}).

Create and show a suspended coupled stripline transmission line

freq = linspace(1e9, 5e9, 41);
s3 = coupledStripLine;
suspendedSubThickness = 0.001;
t1 = s3.Height - suspendedSubThickness; % Thickness of air gap below suspended dielectric
t2 = suspendedSubThickness;             % Thickness of suspended dielectric
t3 = t1 + t2;                           % Thickness of air gap above suspended dielectric
s3.Substrate.Name        = {'Air', 'Teflon', 'Air'};
s3.Substrate.EpsilonR    = [1      2.1       1];
s3.Substrate.LossTangent = [0      2e-4      0];
s3.Substrate.Thickness   = [t1     t2        t3];
s3
s3 = 
  coupledStripLine with properties:

              Length: 0.0207
               Width: 0.0051
             Spacing: 0.0019
              Height: 0.0030
    GroundPlaneWidth: 0.0241
           Substrate: [1x1 dielectric]
           Conductor: [1x1 metal]

figure; show(s3)
title('Suspended coupled stripline');

Figure contains an axes object. The axes object with title Suspended coupled stripline, xlabel x (mm), ylabel y (mm) contains 11 objects of type patch, surface. These objects represent PEC, feed, Teflon.

sp3 = sparameters(s3, freq);
figure; rfplot(sp3, 1:4, 1);
title('Suspended coupled stripline')

Figure contains an axes object. The axes object with title Suspended coupled stripline, xlabel Frequency (GHz), ylabel Magnitude (dB) contains 4 objects of type line. These objects represent dB(S_{11}), dB(S_{21}), dB(S_{31}), dB(S_{41}).

More About

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References

[1] Pozar, Microwave Engineering / David M. Pozar, University of Massachusetts at Amherst.

[2] Cohn, S.B. “Shielded Coupled-Strip Transmission Line.” IEEE Transactions on Microwave Theory and Techniques 3, no. 5 (October 1955): 29–38. https://doi.org/10.1109/TMTT.1955.1124973.

Version History

Introduced in R2024a