stripLine

Create a transmission line in stripline form

Since R2024a

Description

Use the stripLine object to create a transmission line in stripline form. Striplines are high speed transmission lines used for routing various RF components in the inner layers of a multi-layer printed circuit board (PCB). The structure consists of a transmission line trace surrounded by dielectric material suspended between two ground planes.

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

Types and applications of stripline routing techniques:

• Symmetric or Plain — Transmission lines embedded in the internal layers of a PCB equally (symmetrically) spaced between two ground planes.

  Create Symmetric Stripline Transmission Line

• Asymmetric — Transmission lines embedded in the internal layers of a PCB unequally (asymmetrically) spaced between two ground planes.

  Create Asymmetric Stripline Transmission Line

• Suspended — PCB stripline suspended between two parallel ground planes with air gaps between the stripline and the ground planes. This configuration provides higher Q and lower losses than solid dielectric layers.

  Create Suspended Stripline Transmission Line

To create the asymmetric and suspended stripline types every field of Substrate must be expanded into a 1xN vector/cell array, where N is the total number of desired nonmetal layers.

The substrate layers are constructed from bottom to top. The information from Entry 1 of each of these vectors is taken to describe the bottom substrate layer, Entry 2 specifies the second-from-bottom, and so forth.

The stripline’s Height specifies the height of the strip above the bottom ground plane. One of the substrate layers must terminate at exactly Height to avoid an execution error.

The height of the stripline’s top ground plane is automatically set to the total of the thicknesses of all dielectric layers. Note that Height does not govern the height of the top ground plane above the strip.

Note

The value of Height is the height of the strip above the bottom ground plane. For the symmetric stripline the default total PCB thickness - height of the top ground plane above the bottom ground plane - is 2*Height.

Creation

Syntax

strip = stripLine

strip = stripLine(name = value)

Description

strip = stripLine creates a default strip transmission line. The default dimensions are for a frequency range of 1 GHz to 5 GHz. The default transmission line lies in the X-Y plane.

strip = stripLine(name = value) sets Properties using one or more name value arguments. For example, strip = stripLine('Length',0.0300) creates a strip transmission line of length 0.0300 meters. Properties not specified retain their default values.

Properties

Length — Length of strip line

0.0202 (default) | positive scalar

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

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

Data Types: double

Width — Width of strip line

0.0027 (default) | positive scalar

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

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

Data Types: double

Height — Height of strip line

0.0016 (default) | positive scalar

Height of the strip line in meters, specified as a positive scalar.

Example: strip = stripLine('Height',0.0026)

Data Types: double

GroundPlaneWidth — Width of ground plane

0.0150 (default) | positive scalar

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

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

Data Types: double

Substrate — Type of dielectric material

'Teflon' (default) | dielectric object

Type of dielectric material used as a substrate, specified as a dielectric object. The values of the default dielectric material are: ('Name',{'Teflon'},'EpsilonR',2.1, 'LossTangent',0.0002,'Thickness',0.0060) For more information see dielectric.

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

Data Types: string | char

Conductor — Type of metal used for conducting layers

'PEC' (default) | metal object

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

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

Data Types: string | char

Object Functions

charge	Calculate and plot charge distribution
current	Calculate and plot current distribution
design	Design PCB component around particular frequency
feedCurrent	Calculate current at feed port
getZ0	Calculate characteristic impedance of transmission line
mesh	Change and view mesh properties of metal or dielectric in PCB component
show	Display PCB component structure or PCB shape
sparameters	Calculate S-parameters for RF PCB objects
propagationDelay	Compute propagation delay of transmission line
rlgc	Compute resistances, inductances, conductances, and capacitances

Examples

Default Strip Line Transmission Line

Create and view a transmission line in the form of a strip.

txstrip = stripLine

txstrip = 
  stripLine with properties:

              Length: 0.0202
               Width: 0.0027
              Height: 0.0016
    GroundPlaneWidth: 0.0150
           Substrate: [1×1 dielectric]
           Conductor: [1×1 metal]

show(txstrip)

Create Symmetric Stripline Transmission Line

Create, show and analyze a symmetric stripline transmission line

freq = linspace(1e9, 5e9, 41);
s1 = stripLine;
figure; show(s1);
title('Symmetric stripline');

sp1 = sparameters(s1, freq);
figure; rfplot(sp1, 1:2, 1);
title('Symmetric stripline');

Create Asymmetric Stripline Transmission Line

Create, show and analyze an asymmetric stripline transmission line

freq = linspace(1e9, 5e9, 41);
s2 = stripLine;
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 stripline');

sp2 = sparameters(s2, freq);
figure; rfplot(sp2, 1:2, 1)
title('Asymmetric stripline');

Create Suspended Stripline Transmission Line

Create, show and analyze a suspended stripline transmission line

freq = linspace(1e9, 5e9, 41);
s3 = stripLine;
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];
figure; show(s3)
title('Suspended stripline');

sp3 = sparameters(s3, freq);
figure; rfplot(sp3, 1:2, 1);
title('Suspended stripline')

More About

Parametric Analysis

• Decrease the dimensions of the line such as length and width to increase the operating frequency.

• Vary the width of the line to control the characteristic impedance of the line.

• FeedDiameter cannot be increased more than the width of the strip.

Version History

Introduced in R2024a