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

IsShielded — Flag to add metal shielding

false or 0 (default) | true or 1

Flag to add a metal shielding to the PCB component, specified as a logical 0 or logical 1. The default value is logical 0.

Example: IsShielded = true or 1 add a metal shield.

Note

To enable FEM solver required for the metal shield property, download the Integro-Differential Modeling Framework for MATLAB. To download this add-on:

1. In the Home tab Environment section, click on Add-Ons. This opens the add-on explorer. You need an active internet connection to download the add-on.

2. Search for Integro-Differential Modeling Framework for MATLAB and click Install.

3. To verify if the download is successful, run

   matlab.addons.installedAddons

   in your MATLAB^® session command line.

4. On Windows, to run the IDMF add-on, you must install the Windows Subsystem for Linux (WSL). To install WSL, see Install Linux on Windows with WSL.

   The Windows Defender Firewall can block the PostgreSQL server when using the IDMF add-on. To resolve this issue, you can allow the server to communicate on desired networks if the firewall prompts. Alternatively, you can manually add the executable file of the PostgreSQL server located in <matlabroot>\sys\postgresql\win64\PostgreSQL\bin\postgres.exe. For more information, see https://support.microsoft.com/en-us/windows/risks-of-allowing-apps-through-windows-defender-firewall-654559af-3f54-3dcf-349f-71ccd90bcc5c.

Data Types: logical

Shielding — Metal shielding

shape.Box object

This property is read-only.

Metal shield for the PCB component, specified as a shape.Box object. The length and width of the box must be equal to the length and width of the ground plane. The center of the box is at [0 0 Shielding.Height].

Dependencies

To enable the Shielding property, set the IsShielded property to true or 1.

Connector — Type of RF connector

RFConnector object

Type of RF connector assembled at the feed locations of the PCB component, specified as a RFConnector object.

Example: Create connector from RFConnector object like this: coaxial = RFConnector adds a coaxial connector.

Dependencies

To enable the Connector property, set the IsShielded property to true or 1.

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
propagationDelay	Compute propagation delay of transmission line
rlgc	Compute resistances, inductances, conductances, and capacitances
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
RFConnector	Create RF connector

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]
          IsShielded: 0

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]
          IsShielded: 0

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.

Create Shielded Microstrip Transmission Line with Default RF Connector

Create a microstrip transmission line with a metal shield.

microstrip = microstripLine(IsShielded=true)

Warning: SolverType property is changed to 'FEM'.

microstrip = 
  microstripLine with properties:

              Length: 0.0200
               Width: 0.0050
              Height: 0.0016
    GroundPlaneWidth: 0.0300
           Substrate: [1×1 dielectric]
           Conductor: [1×1 metal]
          SolverType: 'FEM'
          IsShielded: 1
           Connector: [1×1 RFConnector]
           Shielding: [1×1 shape.Box]

Display the Connector property whose value is set to a default RFConnector.

microstrip.Connector

ans = 
  RFConnector with properties:

            Name: 'Connector'
     InnerRadius: 5.0000e-04
     OuterRadius: 0.0015
          Flange: [1×1 antenna.Rectangle]
        EpsilonR: 1.7341
    PinFootprint: 'Taper'
       PinLength: 0.0030
       Impedance: 50.0000

View a microstrip transmission line. A tapered trace is added to the both ends of the microstrip transmission line - tapered from a trace width of a microstrip transmission line to an inner diameter of a connector. The length of a tapered trace is controlled by the PinLength property.

show(microstrip)

Set the PinLength property to zero and view a microstrip transmission line. Beware that an outer conductor of a connector must not electrically connected to the signal trace.

microstrip.Connector.PinLength = 0;
microstrip.Connector.OuterRadius = 0.003;
microstrip.Connector.InnerRadius = 0.001;
show(microstrip)

References

[1] Pozar, David M. Microwave Engineering. 4th ed. Hoboken, NJ: Wiley, 2012.

Version History

Introduced in R2021b

R2023b: Metal shielding for microstrip transmission line

Use the IsShielded, Shielding, and Connector properties to add a metal shield to the microStripLine object.