Difference between revisions of "Application Note 3: Designing A Slot-Coupled Patch Antenna Array With A Corporate Feed Network Using EM.Picasso"

From Emagtech Wiki
Jump to: navigation, search
Line 15: Line 15:
 
== Designing the Patch Radiating Element ==
 
== Designing the Patch Radiating Element ==
  
−
Open the [[EM.Cube]] application and switch to [[Planar Module]]. Start a new project with the following attributes:
+
The operating frequency of the patch array is f = 2.4GHz. At this frequency, the free-space wavelength is &lambda;<sub>0</sub> = 125mm. The patch radiators will be spaced at half free-space wavelength: S<sub>x</sub> =  S<sub>y</sub> =  &lambda;<sub>0</sub>/2 = 62.5mm. The design of the slot-coupled patch antenna is described in detail in [[EM.Picasso Tutorial Lesson 7: Designing A Slot-Coupled Patch Antenna]]. The substrate consists of two finite-thickness layers of Roger 4003C separated by a perfect electric conductor (PEC) ground plane of infinite lateral extents. The table below summarizes the substrate stackup's layer hierarchy:
  
−
#Name: EMPicasso_Tutorial_9
+
{| class="wikitable"
−
#Length Units: mm
+
−
#Frequency Units: GHz
+
−
#Center Frequency: 2.4GHz
+
−
#Bandwidth: 1GHz
+
−
#Number of Finite Substrate Layers: 2
+
−
#Layer Stack-up:
+
−
#Top Half-Space: Vacuum
+
−
#Top Layer: ROGER RT/Duroid 5880, &epsilon;<sub>r</sub> = 2.2, &mu;<sub>r</sub> = 1, &sigma; = &sigma;<sub>m</sub> = 0, thickness = 2mm
+
−
#Bottom Layer: ROGER RT/Duroid 5880, &epsilon;<sub>r</sub> = 2.2, &mu;<sub>r</sub> = 1, &sigma; = &sigma;<sub>m</sub> = 0, thickness = 0.787mm
+
−
#Bottom Half-Space: Vacuum
+
−
 
+
−
 
+
−
In this tutorial lesson, you will build a 4&times;1 linear array of the slot-coupled patch antenna elements you already designed in Tutorial Lesson 8. The patch radiators are spaced at half free-space wavelength at the operational frequency of 2.4GHz, which is &lambda;<sub>0</sub>/2 = 62.5mm. You will also build a 1:4 power splitter network on the back of the substrate utilizing three Wilkinson power dividers identical to the one you built earlier in Tutorial Lesson 7.
+
−
 
+
−
For this tutorial lesson, you can build the project structure from the ground up, or you may simply download the project files from our website and starting running simulations immediately.
+
−
 
+
−
==Building the Multilayer Substrate Stack-up==
+
−
 
+
−
The substrate structure of this tutorial lesson is identical to that of Tutorial Lesson 8. Using the table below, build the substrate stack-up of array structure in [[EM.Cube]]'s [[Planar Module]]:   
+
−
 
+
−
{| border="0"
+
−
|-
+
−
| valign="top"|
+
−
| valign="bottom"|
+
−
{| class="wikitable" style="text-align: center;"
+
 
|-
 
|-
 
! scope="col"| Substrate Object Label
 
! scope="col"| Substrate Object Label
Line 50: Line 25:
 
! scope="col"| Thickness
 
! scope="col"| Thickness
 
|-
 
|-
−
! scope="row"| Top Half-Space
+
| Top Half-Space
 
| Half-Space Medium
 
| Half-Space Medium
 
| Top Substrate Termination
 
| Top Substrate Termination
Line 56: Line 31:
 
| Infinite
 
| Infinite
 
|-
 
|-
−
! scope="row"| PEC_1
+
| PEC_1
 
| PEC Trace
 
| PEC Trace
 
| Patch Plane
 
| Patch Plane
Line 62: Line 37:
 
| 0
 
| 0
 
|-
 
|-
−
! scope="row"| Layer 1
+
| Patch Layer
 
| Substrate Layer
 
| Substrate Layer
 
| Patch Substrate
 
| Patch Substrate
Line 68: Line 43:
 
| 2mm
 
| 2mm
 
|-
 
|-
−
! scope="row"| PMC_1
+
| Ground Plane
−
| PMC Trace
+
| Slot (PMC) Trace
 
| Slot Plane
 
| Slot Plane
 
| PMC
 
| PMC
 
| 0
 
| 0
 
|-
 
|-
−
! scope="row"| Layer 2
+
| Layer 2
 
| Substrate Layer
 
| Substrate Layer
 
| Feed Substrate
 
| Feed Substrate
Line 80: Line 55:
 
| 0.787mm
 
| 0.787mm
 
|-
 
|-
−
! scope="row"| PEC_2
+
| PEC_2
 
| PEC Trace
 
| PEC Trace
 
| Microstrip Feed Plane
 
| Microstrip Feed Plane
Line 86: Line 61:
 
| 0
 
| 0
 
|-
 
|-
−
! scope="row"| Bottom Half-Space
+
| Bottom Half-Space
 
| Half-Space Medium
 
| Half-Space Medium
 
| Bottom Substrate Termination
 
| Bottom Substrate Termination

Revision as of 23:22, 16 October 2016

Tutorial Project: Designing A Slot-Coupled Patch Antenna Array With A Corporate Feed Network Using EM.Picasso
PMOM372.png

Objective: In this project, we will build and analyze a 16-element slot-based patch antenna array with a microstrip corporate feed network.

Concepts/Features:

  • CubeCAD
  • PEC Traces
  • SlotTraces
  • Mesh Density
  • Scattering Wave Port
  • Lumped Element
  • Radiation Pattern

Minimum Version Required: All versions

'Download2x.png Download Link: None

Introduction

EM.Picasso can be used to analyze large and fairly complex multilayer planar structures. In this application note, we will show how to use EM.Picasso to design a 4 × 4 slot-coupled patch antenna array with a microstrip corporate feed network. The design process involves three steps: design of the slot-couple patch element, design of the power divider, and finally, construction of the 16-element array. The first two steps are the subject of two of EM.Picasso's tutorial lessons.

Designing the Patch Radiating Element

The operating frequency of the patch array is f = 2.4GHz. At this frequency, the free-space wavelength is λ0 = 125mm. The patch radiators will be spaced at half free-space wavelength: Sx = Sy = λ0/2 = 62.5mm. The design of the slot-coupled patch antenna is described in detail in EM.Picasso Tutorial Lesson 7: Designing A Slot-Coupled Patch Antenna. The substrate consists of two finite-thickness layers of Roger 4003C separated by a perfect electric conductor (PEC) ground plane of infinite lateral extents. The table below summarizes the substrate stackup's layer hierarchy:

Substrate Object Label Substrate Object Type Function Material Thickness
Top Half-Space Half-Space Medium Top Substrate Termination Vacuum Infinite
PEC_1 PEC Trace Patch Plane PEC 0
Patch Layer Substrate Layer Patch Substrate ROGER RT 5880 2mm
Ground Plane Slot (PMC) Trace Slot Plane PMC 0
Layer 2 Substrate Layer Feed Substrate ROGER RT 5880 0.787mm
PEC_2 PEC Trace Microstrip Feed Plane PEC 0
Bottom Half-Space Half-Space Medium Bottom Substrate Termination Vacuum Infinite

Building the Array Structure

The corporate feed network on the microstrip trace plane (PEC_1) consists entirely of rectangle and circle strip objects. For the Wilkinson power dividers, circle strips with unequal outer and inner radii and incomplete start and end angles are used just as you saw in Tutorial Lesson 7. A 50Ω microstrip line on the lower thin substrate has a width of 2.4mm. Small circle strips of (outer) radius 2.4mm are used to provide a round bend junctions between two perpendicular microstrip line segments. Rather than a quarter-circle, a 3/4-circle shape is used to have some good overlap area over the conjoining line objects. This helps with a smoother and more consistent mesh in such junction areas.

Draw the following 9 circle strip objects, all on PEC_2 trace plane, with the given coordinates and dimensions:

Label Host Trace Object Type Function LCS Origin LCS Rotation Angles Outer Radius Inner Radius Start Angle End Angle
Circle_Strip_1 PEC_2 Circle Strip Wilkinson Power Divider 1 (-17mm, 0, 0) (0°, 0°, 0°) 9.65mm 8.25mm 20° 340°
Circle_Strip_2 PEC_2 Circle Strip Wilkinson Power Divider 2 (10mm, 62.5mm, 0) (0°, 0°, 0°) 9.65mm 8.25mm 20° 340°
Circle_Strip_3 PEC_2 Circle Strip Wilkinson Power Divider 3 (10mm, -62.5mm, 0) (0°, 0°, 0°) 9.65mm 8.25mm 20° 340°
Circle_Strip_4 PEC_2 Circle Strip Round Bend Junction (-6.75mm, 61.3mm, 0) (0°, 0°, 0°) 2.4mm 0mm 0° 270°
Circle_Strip_5 PEC_2 Circle Strip Round Bend Junction (-6.75mm, -61.3mm, 0) (0°, 0°, 0°) 2.4mm 0mm 90° 360°
Circle_Strip_6 PEC_2 Circle Strip Round Bend Junction (20.25mm, 92.55mm, 0) (0°, 0°, 0°) 2.4mm 0mm 0° 270°
Circle_Strip_7 PEC_2 Circle Strip Round Bend Junction (20.25mm, -92.55mm, 0) (0°, 0°, 0°) 2.4mm 0mm 90° 360°
Circle_Strip_8 PEC_2 Circle Strip Round Bend Junction (20.25mm, 32.45mm, 0) (0°, 0°, 0°) 2.4mm 0mm 90° 360°
Circle_Strip_9 PEC_2 Circle Strip Round Bend Junction (20.25mm, -32.45mm, 0) (0°, 0°, 0°) 2.4mm 0mm 0° 270°


Rectangle strip objects are used for microstrip line segments. Draw the following 16 rectangle strip objects, all on PEC_2 trace plane, with the given coordinates and dimensions:

Label Host Trace Object Type Function LCS Origin LCS Rotation Angles X Dimension Y Dimension
Rect_Strip_1 PEC_2 Rectangle Strip 50Ω Input Microstrip Feed Line (-38mm, 0, 0) (0°, 0°, 0°) 8mm 2.4mm
Rect_Strip_2 PEC_2 Rectangle Strip 50Ω Input Line for Wilkinson Power Divider 1 (-30mm, 0, 0) (0°, 0°, 0°) 8mm 2.4mm
Rect_Strip_3 PEC_2 Rectangle Strip 50Ω Output Line for Wilkinson Power Divider 1 (-7.95mm, 32.06mm, 0) (0°, 0°, 0°) 2.4mm 58.48mm
Rect_Strip_4 PEC_2 Rectangle Strip 50Ω Output Line for Wilkinson Power Divider 1 (-7.95mm, -32.06mm, 0) (0°, 0°, 0°) 2.4mm 58.48mm
Rect_Strip_5 PEC_2 Rectangle Strip 50Ω Input Line for Wilkinson Power Divider 2 (-2.75mm, 62.5mm, 0) (0°, 0°, 0°) 8mm 2.4mm
Rect_Strip_6 PEC_2 Rectangle Strip 50Ω Input Line for Wilkinson Power Divider 3 (-2.75mm, -62.5mm, 0) (0°, 0°, 0°) 8mm 2.4mm
Rect_Strip_7 PEC_2 Rectangle Strip 50Ω Output Line for Wilkinson Power Divider 2 (19.05mm, 78.935mm, 0) (0°, 0°, 0°) 2.4mm 27.23mm
Rect_Strip_8 PEC_2 Rectangle Strip 50Ω Output Line for Wilkinson Power Divider 3 (19.05mm, -78.935mm, 0) (0°, 0°, 0°) 2.4mm 27.23mm
Rect_Strip_9 PEC_2 Rectangle Strip 50Ω Output Line for Wilkinson Power Divider 2 (19.05mm, 46.065mm, 0) (0°, 0°, 0°) 2.4mm 27.23mm
Rect_Strip_10 PEC_2 Rectangle Strip 50Ω Output Line for Wilkinson Power Divider 3 (19.05mm, -46.065mm, 0) (0°, 0°, 0°) 2.4mm 27.23mm
Rect_Strip_11 PEC_2 Rectangle Strip 50Ω Slot Feed Line (30.125mm, 93.75mm, 0) (0°, 0°, 0°) 19.75mm 2.4mm
Rect_Strip_12 PEC_2 Rectangle Strip 50Ω Slot Feed Line (30.125mm, -93.75mm, 0) (0°, 0°, 0°) 19.75mm 2.4mm
Rect_Strip_13 PEC_2 Rectangle Strip 50Ω Slot Feed Line (30.125mm, 31.25mm, 0) (0°, 0°, 0°) 19.75mm 2.4mm
Rect_Strip_14 PEC_2 Rectangle Strip 50Ω Slot Feed Line (30.125mm, -31.25mm, 0) (0°, 0°, 0°) 19.75mm 2.4mm
Rect_Strip_15 PEC_2 Rectangle Strip Resistor Line for Wilkinson Power Divider 1 (-7.95mm, 0, 0) (0°, 0°, 90°) 5.64mm 1mm
Rect_Strip_16 PEC_2 Rectangle Strip Resistor Line for Wilkinson Power Divider 2 (19.05mm, 62.5mm, 0) (0°, 0°, 90°) 5.64mm 1mm
Rect_Strip_17 PEC_2 Rectangle Strip Resistor Line for Wilkinson Power Divider 3 (19.05mm, -62.5mm, 0) (0°, 0°, 90°) 5.64mm 1mm


You will use array objects to represent the repetitive pattern of slot-coupled patch radiators. Specifically, you will build three array objects for the patch element on the top PEC_1 trace plane, the coupling slot on the middle ground plane PMC_1, and the microstrip open stub underneath the slot on the bottom trace plane PEC_2. The table below shows the coordinate and dimensions of the primitive or "parent" objects for each of these arrays. First, you have to draw these objects on the respective planes:

Label Host Trace Object Type Function LCS Origin LCS Rotation Angles X Dimension Y Dimension
Rect_Strip_18 PEC_2 Rectangle Strip Microstrip Open Stub (51.5mm, -93.75mm, 0) (0°, 0°, 0°) 23mm 2.4mm
Rect_Strip_19 PMC_1 Rectangle Strip Coupling Slot (45mm, -93.75mm, 0.787mm) (0°, 0°, 0°) 1.5mm 12mm
Rect_Strip_20 PEC_1 Rectangle Strip Radiating Patch (45mm, -93.75mm, 2.787mm) (0°, 0°, 0°) 31.6mm 31.6mm


Now, select each of the above primitive objects and use EM.Cube's Array Tool to create a 1×4 Y-directed linear array of that object on the proper plane. Make sure that right trace group on the Navigation Tree is activated before creation of each array object. Use the table below for element count and spacing along the three principal directions.


Attention icon.png Once you create an array object, the array's local coordinate system (LCS) takes over the parent object's LCS. The array's LCS rotation angles are independent of the parent object's rotation angles.
Label Host Trace Primitive Object Array LCS Origin Array LCS Rotation Angles X Count Y Count Z Count X Spacing Y Spacing Z Spacing
Rect_Strip_18 PEC_2 Rect_Strip_18 (51.5mm, -93.75mm, 0) (0°, 0°, 0°) 1 4 1 0 62.5mm 0
Rect_Strip_19 PMC_1 Rect_Strip_19 (45mm, -93.75mm, 0) (0°, 0°, 0°) 1 4 1 0 62.5mm 0
Rect_Strip_20 PEC_1 Rect_Strip_20 (45mm, -93.75mm, 0) (0°, 0°, 0°) 1 4 1 0 62.5mm 0


The geometry of the 4-element slot-coupled patch antenna array with a corporate feed network.


Next, define three lumped elements of "Resistor" type with a 100Ω value and place them in the middle of the line segments Rect_Strip_15, Rect_Strip_16 and Rect_Strip_17. Also define a default +X-directed de-embedded source on the line object Rect_Strip_1 and assign a default Port Definition observable to it. Define three Current Distribution observables for the PEC_1, PEC_2 and PMC_1 traces. Define a Far Fields Radiation Pattern observable with a 3° Angle Increment for both Theta and Phi, and check its Front-to-Back Ratio (FBR) checkbox. Your antenna array is complete at this point.


The Planar MoM Mesh Settings dialog.

Examining the Mesh of the Planar Array

Similar to Tutorial Lessons 7 and 8, set the mesh density to 40 cells per effective wavelength. Open the Mesh Settings dialog and increase the minimum angle of defective triangular cells to 20°. Also, check the checkbox labeled " Refine Mesh at Gap Locations". This is due to the presence of three lumped elements on very narrow line objects. In EM.Cube's Planar Module, lumped elements behave very similar to gap sources.

Generate and view the planar MoM mesh of your array structure on all three PEC_1, PMC_1 and PEC_2 planes. The mesh of the corporate feed network is the most complicated one and requires special attention. In particular, closely inspect the mesh at the junctions of microstrip line segments with the Wilkinson circular rings and the around the round corner bend junctions. Also examine the connections to the open stub array. Connections to array objects might sometime be tricky in complicated configurations.


Attention icon.png If your planar structure involves a large number of interconnected objects, individual objects with curved shapes, many overlap regions and several gap sources or lumped elements, EM.Cube's mesh generator may fail with low mesh density values. You may be asked to increase the mesh density.


The Planar MoM mesh of the 4-element slot-coupled patch antenna array with a corporate feed network.
Details of the planar mesh around the Wilkinson power divider.
Details of the planar mesh around the round corner bend junctions.

Running a Planar MoM Analysis of the Antenna Array

Run a quick planar MoM analysis of your slot-couple patch array structure. The size of the linear system in this case is N = 3,546. At the end of the simulation, the following port characteristic values are reported in the Output Message Window:

S11: -0.197431 - 0.916521j

S11(dB): -0.560162

Z11: 2.660904 - 40.306972j

Y11: 0.001631 + 0.024702j

Note that input match of the array has been seriously degraded compared to that of the single slot-coupled patch antenna you built in Tutorial Lesson 8. Visualize all three current distributions on the PEC_1, PEC_2 and PMC_1 trace planes. You may have to change the limits of the current plot for the feed network due to the presence of a few very hot spots around the line discontinuities.


The surface electric current distribution on the microstrip feed network of the array after limiting the plot values to 99% confidence interval.
The surface electric current distribution on the top patches of the array.
The surface magnetic current distribution on the coupling slots of the array.

Also visualize the 3D radiation pattern of your patch antenna array and plot the 2D Cartesian and polar graphs in EM.Grid. Note the portion of the radiation pattern in the lower half-space (90° ≤ θ ≤ 180°). This is due to the radiation from the feed network. Open the Data Manager and view the contents of the data file "FBR.DAT". You will see a value of 2.304221e-002 for the front-to-back ratio of the slot-coupled patch array. But it important to note that the computed FBR value is ratio of the total far field value at θ = 180° to the total far field value at θ = 0°. A close inspection of the patterns in the lower half-space reveals that the back lobes peak at θ = 130°, not at θ = 180°. The directivity of the antenna array is found to be 11.15 (or 10.47dB).


The 3D radiation pattern of the slot-coupled patch antenna array with a corporate feed network.
The 2D Cartesian graph of the YZ-plane radiation pattern of the slot-coupled patch antenna array.
The 2D Cartesian graph of the ZX-plane radiation pattern of the slot-coupled patch antenna array.
The 2D polar graph of the YZ-plane radiation pattern of the slot-coupled patch antenna array.
The 2D polar graph of the ZX-plane radiation pattern of the slot-coupled patch antenna array.


The 3D radiation pattern of a single stand-alone slot-coupled patch antenna multiplied by a 4×1 array factor.

Comparison with Array Factor Method

In Tutorial Lesson 8, you could have defined a linear array factor in the Radiation Pattern dialog of the slot-couple patch antenna. Had you done that, the computed radiation pattern would have corresponded to an array of slot-coupled patch antennas rather than the single stand-alone radiator appearing your project workspace. However, the array pattern computed in this manner does not account for the inter-element coupling effects. The figures below have been obtained by multiplying the radiation pattern of the single slot-coupled patch antenna by a 1×4 Y-directed array factor with an element spacing of 62.5mm. The directivity of the array is calculated to be 12.15 (or 10.89dB), which is fairly close to the directivity of the array with the corporate feed network. Comparing the two sets of radiation pattern plots, you can see that even the side lobe and nulls are very similar in both cases. The main difference, however, is in the back lobe characteristics.


The 2D Cartesian graph of the YZ-plane radiation pattern of a single stand-alone slot-coupled patch antenna multiplied by a 4×1 array factor.
The 2D Cartesian graph of the ZX-plane radiation pattern of a single stand-alone slot-coupled patch antenna multiplied by a 4×1 array factor.
The 2D polar graph of the YZ-plane radiation pattern of a single stand-alone slot-coupled patch antenna multiplied by a 4×1 array factor.
The 2D polar graph of the ZX-plane radiation pattern of a single stand-alone slot-coupled patch antenna multiplied by a 4×1 array factor.





PMOM372.png EM.Picasso Tutorials :


Back to EM.Cube Wiki Main Page

Retrieved from "http://www.emagtech.com/wiki/index.php?title=Application_Note_3:_Designing_A_Slot-Coupled_Patch_Antenna_Array_With_A_Corporate_Feed_Network_Using_EM.Picasso&oldid=32466"