microstripLine

Create transmission line in microstrip form

Since R2021b

Description

Use the microstripLine object to create a microstrip transmission line. A 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 two PCB components or to create components such as filters, couplers, and feeding elements of various types of antennas.

Note

This PCB object supports behavioral modeling. For more information, see Behavioral Models. To analyze the behavioral model for a microstrip transmission line, set the Behavioral property in the sparameters function to true or 1

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

Creation

Syntax

microstrip = microstripLine

microstrip = microstripLine(Name=Value)

microstrip = microstripLine(txlineobj)

Description

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

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

Length — Length of microstrip line

0.0200 (default) | positive scalar

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

Example: microstrip = microstripLine(Length=0.0300)

Data Types: double

Width — Width of microstrip line

0.0050 (default) | positive scalar

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

Example: microstrip = microstripLine(Width=0.00630)

Data Types: double

Height — Height of microstrip line

0.0016 (default) | positive scalar

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

In the 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

GroundPlaneWidth — Width of ground plane

0.0300 (default) | positive scalar

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

Example: microstrip = microstripLine(GroundPlaneWidth=0.0400)

Data Types: double

Substrate — Type of dielectric material

dielectric object

Type of dielectric material used as a substrate, specified as a dielectric object. For more information, see dielectric. The dielectric material in a microstripLine object with default properties is Teflon. 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

Conductor — Type of metal used in conducting layers

metal object

Type of metal used in conducting layers, specified as a metal object. For more information see metal. The type of metal in a microstripLine object with default properties is PEC.

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

Data Types: string | char

Object Functions

charge	Calculate and plot charge distribution
current	Calculate and plot current distribution
design	Design microstrip transmission line around specified frequency
feedCurrent	Calculate current at feed port
getZ0	Calculate characteristic impedance of transmission line
layout	Plot all metal layers and board shape
mesh	Change and view mesh properties of metal or dielectric in PCB component
shapes	Extract all metal layer shapes of PCB component
show	Display PCB component structure or PCB shape
sparameters	Calculate S-parameters for RF PCB objects

Examples

Default Microstrip Line

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)

Microstrip Transmission Line at 3 GHz

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: [1x1 dielectric]
           Conductor: [1x1 metal]

View the microstrip transmission line.

show(microstrip)

Multilayer Dielectric Microstrip Transmission Line

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);

Use Behavioral Model to Calculate S-Parameters of Microstrip Cross

Design a microstrip transmission line at 3 GHz using 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)

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.

Use Behavioral Model to Calculate S-Parameters of Mitered Bend Microstrip

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)

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')

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. 4th ed. Hoboken, NJ: Wiley, 2012.

Version History

Introduced in R2021b