models.rf.sma connectorized gcpw

7/22/2019 Models.rf.Sma Connectorized Gcpw

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Solved with COMSOL Multiphysics 4.4

1 | S M A C O N N E C T O R O N A G R O U N D E D C O P L A N A R W A V E G U I D E

SMA Conn e c t o r on a G r ound ed

Cop l a n a r Wave gu i d e

Introduction

SMA connectors are popularly used on printed circuit boards (PCB) for testing. This

model shows how to excite an SMA connector on a microwave substrate and how to

terminate a grounded coplanar waveguide (GCPW) with 50 using a lumped portand an air-bridge.

Coaxial lumped port

Metalized vias

Air-bridge

SMA connector

60 mil substrate with a ground plane

Figure 1: An SMA connector is soldered onto a GCPW line. The other end of the GCPWline is terminated with 50 ohms using a lumped port.

Model Definition

The purpose of this model is to show how to excite a grounded coplanar waveguide

with the signal from a coaxial cable through an SMA connector. The model also

illustrates a particular 50 passive termination constructed with an air-bridge.


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The signal in the coaxial cable is carried by the TEM mode at 1 GHz. Inside the cable,

the electric field of the TEM mode points radially between the inner and outer

conductors. (In the cross-section of the cable, the electric field is the same as theelectrostatic field with a DC voltage between the conductors.) This field passes

through the SMA connector and excites a symmetric mode of the coplanar waveguide.

The symmetric electric field in the coplanar waveguide points from the center

conductor outwards to the conductors on either side, or depending on the phase,

inwards from the outer conductors towards the center conductor.

The ground plane on the bottom of the PCB with r= 3.38 is connected to the outer

conductors of the CPW with metalized vias to prevent unwanted surface waves.

The domain between the inner and outer conductor of the SMA connector is filled

with Teflon and all metal parts including the SMA connector, CPW, metalized vias and

air-bridge are modeled as perfect electric conductor. The entire modeling domain is

bounded by scattering boundaries that represent an open space except the ground

plane.

Horizontal configurationVertical configurationusing an air-bridge

Figure 2: Two ways to add a port on a CPW

This example evaluates the passive 50 termination on the GCPW in two ways

(Figure 2). One is extending the lumped port horizontally from the center conductor

to the outer conductor of the GCPW. The other is using an air-bridge which extends

above the substrate and connects the outer conductors while maintaining an air gap

between itself and the center conductor. In this case, the lumped port extends

vertically from the center conductor to the air-bridge.

All domains are meshed by a tetrahedral mesh with maximum element size of five

elements per wavelength so that the wave is well-resolved. The parts in SMA connector

and vias are meshed more finely to provide good resolution of the curved surfaces.


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Results and Discussion

The norm of electric fields is plotted in Figure 3. The plot setting is modified to showthe fields on xy-plane confined between the center conductor and outer conductor

(ground plane) of the GCPW. The evaluated S-parameters for both passive termination

methods are approximately -24 dB.

Figure 3: The plotted electric field distribution is symmetric due to the geometry set up.

Model Library path: RF_Module/Transmission_Lines_and_Waveguides/

sma_connectorized_gcpw


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Modeling Instructions

From the Filemenu, choose New.

N E W

1 In the Newwindow, click the Model Wizardbutton.

M O D E L W I Z A R D

1 In the Model Wizardwindow, click the 3Dbutton.

2 In the Select physicstree, select Radio Frequency>Electromagnetic Waves, Frequency

Domain (emw).

3 Click the Addbutton.

4 Click the Studybutton.

5 In the tree, select Preset Studies>Frequency Domain.

6 Click the Donebutton.

G E O M E T R Y 1

1 In the Model Builderwindow, under Component 1click Geometry 1.

2 In the Geometrysettings window, locate the Unitssection.

3 From the Length unitlist, choose mm.

G L O B A L D E F I N I T I O N S

Parameters

1 On the Hometoolbar, click Parameters.

2 In the Parameterssettings window, locate the Parameterssection.


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3 In the table, enter the following settings:

Here, c_constis a predefined COMSOL constant for the speed of light in vacuum.

G E O M E T R Y 1

Block 1

1 On the Geometrytoolbar, click Block.

2 In the Blocksettings window, locate the Sizesection.

3 In the Widthedit field, type 60.

4 In the Depthedit field, type 40.

5 In the Heightedit field, type 20.

6 Locate the Positionsection. In the yedit field, type -5.

7 Click the Wireframe Renderingbutton on the Graphics toolbar.

Block 2




4 In the Depthedit field, type 30.

5 In the Heightedit field, type 1.524.

6 Click the Build Selectedbutton.

Work Plane 1

1 On the Geometrytoolbar, click Work Plane.

2 In the Work Planesettings window, locate the Plane Definitionsection.

NAME EXPRESSION VALUE DESCRIPTION

r_inner 0.635[mm] 6.3500E-4 m Coax, inner radius

r_outer 2.05[mm] 0.0020500 m Coax, outer radius

l_sma 8[mm] 0.0080000 m SMA, pin length

w_c 2.8[mm] 0.0028000 m CPW, center conductorwidth

w_s 5.8[mm] 0.0058000 m CPW, center conductorand slot width

f0 1[GHz] 1.0000E9 Hz Frequency

lda0 c_const/f0 0.29979 m Wavelength


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3 From the Plane typelist, choose Face parallel.

4 Select the object blk2only.

5 Click the Activebutton next to the Planar faceselection list.

6 On the object blk2, select Boundary 4 only.

Rectangle 1

1 In the Model Builderwindow, under Component 1>Geometry 1>Work Plane 1

right-click Plane Geometryand choose Rectangle.

2 In the Rectanglesettings window, locate the Sizesection.


4 In the Heightedit field, type w_c.

5 Locate the Positionsection. In the xwedit field, type -30.

6 In the ywedit field, type -w_c/2.

Rectangle 2

1 Right-click Plane Geometryand choose Rectangle.



4 In the Heightedit field, type w_s.


6 In the ywedit field, type -w_s/2.

Rectangle 31 Right-click Plane Geometryand choose Rectangle.





6 In the ywedit field, type -w_s/2.

Rectangle 4



3 In the Heightedit field, type w_c.



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5 In the ywedit field, type -w_c/2.

Difference 1

1 On the Work planetoolbar, click Difference.

2 Select the object r1only.

3 In the Differencesettings window, locate the Differencesection.

4 Click the Activebutton next to the Objects to subtractselection list.


6 Select the Keep input objectscheck box.

Union 1

1 On the Work planetoolbar, click Union.

2 Select the objects r3, r1, and dif1only.

Cylinder 1

1 On the Geometrytoolbar, click Cylinder.

2In the

Cylindersettings window, locate the

Size and Shapesection.

3 In the Radiusedit field, type r_inner.

4 In the Heightedit field, type l_sma+3.

5 Locate the Positionsection. In the xedit field, type -l_sma.

6 In the yedit field, type 15.

7 In the zedit field, type 1.524+r_inner.

8 Locate the Axissection. From the Axis typelist, choose x-axis.

Cylinder 2


2 In the Cylindersettings window, locate the Size and Shapesection.

3 In the Radiusedit field, type r_outer.

4 In the Heightedit field, type l_sma.

5 Locate the Positionsection. In the xedit field, type -l_sma.6 In the yedit field, type 15.



Cylinder 3



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3 In the Radiusedit field, type r_outer+0.6.

4 In the Heightedit field, type l_sma.

5 Locate the Positionsection. In the xedit field, type -l_sma.




Difference 11 On the Geometrytoolbar, click Difference.

2 Select the object cyl3only.




6 Select the Keep input objectscheck box.

Block 3




4 In the Depthedit field, type r_inner*2.

5In the

Heightedit field, type

r_inner.

6 Locate the Positionsection. In the yedit field, type 15-r_inner.

7 In the zedit field, type 1.524.

Work Plane 2



3 From the Plane typelist, choose Face parallel.4 Click the Activebutton next to the Planar face selection list.

5 On the object dif1, select Boundary 10 only.

Square 1


right-click Plane Geometryand choose Square.


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2 In the Squaresettings window, locate the Sizesection.

3 In the Side lengthedit field, type 12.7.

4 Locate the Positionsection. From the Baselist, choose Center.

Circle 1

1 Right-click Plane Geometryand choose Circle.

2 In the Circlesettings window, locate the Size and Shapesection.

3 In the Radiusedit field, type 1.3.

4 Locate the Positionsection. In the xwedit field, type -4.3.

5 In the ywedit field, type -4.3.

Array 1

1 On the Work planetoolbar, click Array.

2 Select the object c1only.

3 In the Arraysettings window, locate the Sizesection.

4 In the xw sizeedit field, type 2.

5 In the yw sizeedit field, type 2.

6 Locate the Displacementsection. In the xwedit field, type 8.6.

7 In the ywedit field, type 8.6.

Chamfer 1

1 On the Work planetoolbar, click Chamfer.

2 On the object sq1, select Points 14 only.3 In the Chamfersettings window, locate the Distancesection.

4 In the Distance from vertexedit field, type 1.

Circle 2

1 Right-click Plane Geometryand choose Circle.

2 In the Circlesettings window, locate the Size and Shapesection.

3 In the Radiusedit field, type 2.05.

Extrude 1

1 On the Geometrytoolbar, click Extrude.

2 In the Extrudesettings window, locate the Distances from Planesection.


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4 Click the Build Selectedbutton.

Delete Entities 1

1 In the Model Builderwindow, right-click Geometry 1and choose Delete Entities.

2 In the Delete Entitiessettings window, locate the Entities or Objects to Deletesection.

3 From the Geometric entity levellist, choose Domain.4 On the object ext1, select Domains 26 only.

Union 1

1 On the Geometrytoolbar, click Union.

2 Select the objects dif1, cyl1, del1, and blk3only.

3 In the Unionsettings window, locate the Unionsection.

4 Clear the Keep interior boundariescheck box.

Cylinder 4




4 Locate the Positionsection. In the xedit field, type 5.


Array 1

1 On the Geometrytoolbar, click Array.


3 In the Arraysettings window, locate the Sizesection.

4 In the x sizeedit field, type 11.

5 In the y sizeedit field, type 2.

6 Locate the Displacementsection. In the xedit field, type 5.


Work Plane 3


DISTANCES (MM)

-1.65


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3 From the Planelist, choose zy-plane.

4 In the x-coordinateedit field, type 54.

Rectangle 1


right-click Plane Geometryand choose Rectangle.



4 Locate the Positionsection. In the xwedit field, type 1.524.


Rectangle 2



3 In the Widthedit field, type 1.6.




Difference 1

1 On the Work planetoolbar, click Difference.





Rectangle 3







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6 On the Hometoolbar, click Build All.

The finished geometry should look like this.

The inside metal body of the SMA connector and vias are not part of the model

domain. By removing from the model domain, the exterior boundaries of those parts

are set to PEC by default.

E L E C T R O M A G N E T I C W A V E S , F R E Q U E N C Y D O M A I N

1 In the Model Builderwindow, under Component 1click Electromagnetic Waves,Frequency Domain.

2 In the Electromagnetic Waves, Frequency Domainsettings window, locate the Domain

Selectionsection.

3 Click Clear Selection.

4 Select Domains 2, 5, and 6 only.

Perfect Electric Conductor 21 On the Physicstoolbar, click Boundariesand choose Perfect Electric Conductor.

2 In the Perfect Electric Conductorsettings window, locate the Boundary Selection

section.

3 Click Paste Selection.

4 Go to the Paste Selectiondialog box.


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5 In the Selectionedit field, type 55, 56, 67, 79, 213, 222, 223, 224.

6 Click the OKbutton.

Lumped Port 1

1 On the Physicstoolbar, click Boundariesand choose Lumped Port.

2 Select Boundary 4 only.

3 In the Lumped Portsettings window, locate the Lumped Port Propertiessection.

4 From the Type of portlist, choose Coaxial.

5 From the Wave excitation at this portlist, choose On.

Lumped Port 2

1 On the Physicstoolbar, click Boundariesand choose Lumped Port.


Scattering Boundary Condition 1

1 On the Physicstoolbar, click Boundariesand choose Scattering Boundary Condition.

2 Select Boundaries 49, 50, 52, 53, 81, 84, 227, and 228 only.

M A T E R I A L S

Mater ial 1

1 In the Model Builderwindow, under Component 1right-click Materialsand choose

New Material.

2 In the Materialsettings window, locate the Material Contentssection.


Mater ial 2

1 In the Model Builderwindow, right-click Materialsand choose New Material.

2 Select Domain 2 only.


PROPERTY NAME VALUE UNIT PROPERTY GROUP

Relative permittivity epsilonr 1 1 Basic

Relative permeability mur 1 1 Basic

Electrical conductivity sigma 0 S/m Basic


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Mater ial 3

1 Right-click Materialsand choose New Material.




M E S H 1

Size 1

1 In the Model Builderwindow, under Component 1right-click Mesh 1and choose Size.

2 In the Sizesettings window, locate the Element Sizesection.

3 Click the Custombutton.

4 Locate the Element Size Parameterssection. Select the Maximum element sizecheck

box.

5 In the associated edit field, type lda0/5.

Size 2

1 In the Model Builderwindow, right-click Mesh 1and choose Size.

2 In the Sizesettings window, locate the Geometric Entity Selectionsection.

3 From the Geometric entity levellist, choose Domain.


5 Locate the Element Sizesection. Click the Custombutton.

6 Locate the Element Size Parameterssection. Select the Maximum element sizecheck

box.


Relative permittivity epsilonr 2.1 1 Basic




Relative permittivity epsilonr 3.38 1 Basic




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7 In the associated edit field, type lda0/5/sqrt(3.38).

Size 3

1 Right-click Mesh 1and choose Size.


3 From the Geometric entity levellist, choose Domain.

4 Select Domains 13 and 7 only.

5 Locate the Element Sizesection. From the Predefinedlist, choose Fine.

Size 4

1 Right-click Mesh 1and choose Size.


3 From the Geometric entity levellist, choose Boundary.

4 Select Boundaries 61, 67, 77, and 213215 only.

5 Locate the Element Sizesection. From the Predefinedlist, choose Extremely fine.

Free Tetrahedral 11 Right-click Mesh 1and choose Free Tetrahedral.

2 In the Model Builderwindow, under Component 1>Mesh 1right-click Free Tetrahedral

1and choose Build All.

D E F I N I T I O N S

View 1

1 In the Model Builderwindow, under Component 1>Definitionsright-click View 1andchoose Hide Geometric Entities.

2 In the Hide Geometric Entitiessettings window, locate the Geometric Entity Selection

section.

3 From the Geometric entity levellist, choose Boundary.

4 Select Boundaries 49, 50, 52, 84, and 227 only.


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M E S H 1

S T U D Y 1

Step 1: Frequency Domain

1 In the Model Builderwindow, under Study 1click Step 1: Frequency Domain.

2 In the Frequency Domainsettings window, locate the Study Settingssection.3 In the Frequenciesedit field, type 1[GHz].

4 On the Hometoolbar, click Compute.

R E S U L T S

Electric Field (emw)

1 In the Multislicesettings window, locate the Multiplane Datasection.

2 Find the x-planessubsection. In the Planesedit field, type 0.

3 Find the y-planessubsection. In the Planesedit field, type 0.

4 Find the z-planessubsection. From the Entry methodlist, choose Coordinates.

5 In the Coordinatesedit field, type 1.524.

6 Click to expand the Rangesection. Select the Manual color rangecheck box.


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7 In the Maximumedit field, type 1500.

8 On the Electric Field (emw) toolbar, click Plot.

Derived Values

1 On the Resultstoolbar, click Global Evaluation.

2 In the Global Evaluationsettings window, click Replace Expressionin the upper-right

corner of the Expressionsection. From the menu, choose Electromagnetic Waves,

Frequency Domain>Ports>S-parameter, dB (emw.S11dB).

3 Click the Evaluatebutton.

Place the listener port between the CPW center conductor and air-bridge. Compute

again.

E L E C T R O M A G N E T I C W A V E S , F R E Q U E N C Y D O M A I N

Lumped Port 2

1 In the Model Builderwindow, under Component 1>Electromagnetic Waves, Frequency

Domainclick Lumped Port 2.

2 In the Lumped Portsettings window, locate the Boundary Selectionsection.

3 Click Clear Selection.


S T U D Y 1

On the Hometoolbar, click Compute.

R E S U L T S

Derived Values

1 On the Resultstoolbar, click Global Evaluation.

2 In the Global Evaluationsettings window, click Replace Expressionin the upper-right

corner of the Expressionsection. From the menu, choose Electromagnetic Waves,

Frequency Domain>Ports>S-parameter, dB (emw.S11dB).

3 Click the Evaluatebutton.


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models.rf.sma connectorized gcpw

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