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microstripLine

Create transmission line in microstrip form

Description

Use the microstripLine object to create a microstrip transmission line. Microstrip line is a transmission line that is a basic building block for most RF planar microwave devices. You can use this transmission line to connect between two PCB components or to create components such as filters, couplers, and feeding elements of various types of antennas.

A few applications of microstrip transmission lines are:

  • Creating matching feed and coupling networks

  • Transmitting power from one component to another

  • Feeding planar antennas and coupling structures

  • Creating varying inductances or capacitances using open- or short ended- transmission lines

To analyze the behavioral model for a microstrip transmission line, set the Behavioral property in the sparameters function to true or 1.

Creation

Description

example

microstrip = microstripLine creates a default microstrip transmission line using a Teflon substrate.

example

microstrip = microstripLine(Name,Value) sets properties using one or more name value pair arguments. For example, microstrip = microstripLine('Length',0.0300) creates a microstrip line of length 0.0300 meters. Properties not specified retain their default values.

microstrip = microstripLine(txlineobj) creates a microstrip transmission line from the behavioral model of a txlineMicrostrip object in RF Toolbox™.

Properties

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Length of the microstrip line in meters, specified as a positive scalar.

Example: microstrip = microstripLine('Length',0.0300)

Data Types: double

Width of the microstrip line in meters, specified as a positive scalar.

Example: microstrip = microstripLine('Width',0.00630)

Data Types: double

Height of the microstrip line from the ground plane in meters, specified as a positive scalar.

In case of a multilayer substrate, you can use the height property to create a microstrip line at the interface of the two dielectrics.

Example: microstrip = microstripLine('Height',0.0015)

Data Types: double

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

Example: microstrip = microstripLine('GroundPlaneWidth',0.0400)

Data Types: double

Type of dielectric material used as a substrate, specified as a dielectric object. For more information, see dielectric. The thickness of the default dielectric material Teflon is 0.0016 m or the same as the height property.

Example: d = dielectric('FR4'); microstrip = microstripLine('Substrate',d)

Data Types: string | char

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

Example: m = metal('PEC'); microstrip = microstripLine('Conductor',m)

Data Types: string | char

Object Functions

chargeCalculate and plot charge distribution
currentCalculate and plot current distribution
designDesign microstrip transmission line around specified frequency
feedCurrentCalculate current at feed port
getZ0Calculate characteristic impedance of transmission line
layoutPlot all metal layers and board shape
meshChange and view mesh properties of metal or dielectric in PCB component
shapesExtract all metal layer shapes of PCB component
showDisplay PCB component structure or PCB shape
sparametersCalculate S-parameters for RF PCB objects

Examples

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Create and view a default microstrip transmission line.

microstrip = microstripLine
microstrip = 
  microstripLine with properties:

              Length: 0.0200
               Width: 0.0050
              Height: 0.0016
    GroundPlaneWidth: 0.0300
           Substrate: [1x1 dielectric]
           Conductor: [1x1 metal]

show(microstrip)

Figure contains an axes object. The axes object with title microstripLine element contains 6 objects of type patch, surface. These objects represent PEC, feed, Teflon.

Design a microstrip transmission line at 3 GHz, with a characteristic impedance of 70 ohms and a line length 1.5 times the wavelength.

microstrip = design(microstripLine,3e9,'Z0',70,'LineLength',1.5)
microstrip = 
  microstripLine with properties:

              Length: 0.1132
               Width: 0.0030
              Height: 0.0016
    GroundPlaneWidth: 0.0150
           Substrate: [1×1 dielectric]
           Conductor: [1×1 metal]

View the microstrip transmission line.

show(microstrip)

Create and view a multilayer dielectric microstrip transmission line.

microstrip = microstripLine;
microstrip.Substrate = dielectric('Name',{'Teflon','Teflon'},'EpsilonR', ...
    [2.1 2.1],'LossTangent',[0 0],'Thickness',[0.8e-3 0.8e-3]);
    microstrip.Height = 0.8e-3;
show(microstrip);

Design a microstrip transmission line at 3 GHz for FR4 substrate.

d = dielectric('FR4');
d.LossTangent = 0;
m = design(microstripLine('Substrate',d),3e9,'Z0',75,...
    'LineLength',0.5);

Create a microstrip cross.

layer2d = traceCross('Length',[m.Length m.Length], ...
    'Width',[m.Width m.Width]);

Convert the cross trace to a PCB component.

robj = pcbComponent(layer2d);
robj.BoardThickness = m.Substrate.Thickness;
robj.Layers{2} = m.Substrate;
show(robj)

Figure contains an axes object. The axes object with title pcbComponent element contains 9 objects of type patch, surface. These objects represent PEC, feed, FR4.

Define frequency points to calculate the s-parameters.

freq = (1:3:40)*100e6;

Calculate the s-parameters of the cross trace using the behavioral model.

Sckt = sparameters(robj,freq,'Behavioral',true);
Warning: Behavioral model is valid only when EpsilonR is 9.9.

Calculate the s-parameters of the cross trace using the electromagnetic solver.

Sem = sparameters(robj,freq);

References:

  1. Ramesh Garg & I. J. Bahl (1978) Microstrip discontinuities, International Journal of Electronics, 45:1, 81-87, DOI: 10.1080/00207217808900883

  2. Wadell, Brian C. Transmission Line Design Handbook. The Artech House Microwave Library. Boston: Artech House, 1991.

Create mitered bend microstrip.

m = design(microstripLine,6e9,"Z0",75);
layer2d = bendMitered('Length',[m.Length/2 m.Length/2],...
"Width",[m.Width m.Width],'MiterDiagonal',sqrt(2)*m.Width);
robj = pcbComponent(layer2d);
robj.BoardThickness = m.Substrate.Thickness;
robj.Layers{2} = m.Substrate;
show(robj)

Figure contains an axes object. The axes object with title pcbComponent element contains 7 objects of type patch, surface. These objects represent PEC, feed, Teflon.

Compute and plot s-parameters.

freq = (1:2:60)*100e6;
Sckt = sparameters(robj,freq,'Behavioral',true);
Sem = sparameters(robj,freq);
rfplot(Sckt,1,1,'db','-s')
hold on
rfplot(Sem,1,1,'db','-x')

Figure contains an axes object. The axes object contains 2 objects of type line. These objects represent dB(S_{11}).

Reference:

M. Kirschning, R. H. Jansen and N. H. L. Koster, "Measurement and Computer-Aided Modeling of Microstrip Discontinuities by an Improved Resonator Method," 1983 IEEE MTT-S International Microwave Symposium Digest, Boston, MA, USA, 1983, pp. 495-497, doi: 10.1109/MWSYM.1983.1130959.

References

[1] Pozar, David M. Microwave Engineering / David M. Pozar, University of Massachusetts at Amherst, 2012. https://public.ebookcentral.proquest.com/choice/publicfullrecord.aspx?p=2064708.

Introduced in R2021b