EM.Picasso Tutorial Lesson 7: Designing A Slot-Coupled Patch Antenna

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Tutorial Project: Designing A Slot-Coupled Patch Antenna
Picasso L7 Fig title.png

Objective: In this project, you will build a multilayer slot-coupled patch antenna and investigate its near-field and far-field characteristics.

Concepts/Features:

  • CubeCAD
  • Stack-up Manager
  • PEC Trace
  • Slot Trace
  • Electric Surface Current Distribution
  • Magnetic Surface Current Distribution
  • S-Parameters
  • Variables
  • Parametric Sweep

Minimum Version Required: All versions

'Download2x.png Download Link: EMPicasso_Lesson7

What You Will Learn

In this tutorial you will simulate multilayer planar structures that contain several metal and slot objects located on different trace planes. You will also learn how to set up a constrained parametric sweep that ties up different object parameters.

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The substrate layer configuration of the slot-coupled patch antenna.

Getting Started

Open the EM.Cube application and switch to EM.Picasso. Start a new project with the following parameters:

Starting Parameters
Name EMPicasso_Lesson7
Length Units Millimeters
Frequency Units GHz
Center Frequency 2.4GHz
Bandwidth 1GHz
Substrate Configuration
Number of Finite Layers 2
Top Half-Space Vacuum
Top Layer ROGER RO 4003C: εr = 3.38, σ = 0, thickness = 2mm
Bottom Layer ROGER RO 4003C: εr = 3.38, σ = 0, thickness = 0.787mm
Bottom Half-Space Vacuum

Creating the Slot-Coupled Patch Antenna Geometry

Click on the Slot-Coupled Patch Wizard SlotCoupledPatchWizardIcon.png button of the Wizard Toolbar or select the menu item Tools → Antenna Wizards → Slot-Coupled Patch Antenna.

EM.Picasso's wizard toolbar.

The wizard creates the geometry of the patch antenna in the project workspace.

The geometry of the slot-coupled patch antenna created by the wizard in the project workspace. The top patch object is shown in a mouse-over state.

Open the variables dialog and change the definition of the following variables:

Variable Name Original Definition New Definition
er_patch 2.2 3.38
h_patch 0.0015*to_meters 2
er_feed 2.2 3.38
h_feed 0.0015*to_meters 0.787
feed_len 0.1*to_meters 30
slot_len 0.025*to_meters 12
slot_wid 0.0025*to_meters 1.5

The variables list now looks like this:

The variables dialog showing the new values of some variables.

The wizard created three trace plane according to the table below:

Trace Label Trace Type Function Trace Location
PATCH_PEC PEC Trace Patch Plane Between Top Substrate Layer and Top Half-Space
SLOT Slot Trace Coupling Slot Plane Between Top Substrate Layer and Bottom Substrate Layer
FEED_PEC PEC Trace Microstrip Feed Plane Between Bottom Substrate Layer and Bottom Half-Space

Examining the Multilayer Substrate's Layer Hierarchy

Open EM.Picasso's stackup manager dialog and inspect the hierarchy of the substrate layers and interspersed trace planes.

The stackup settings dialog showing the substrate configuration of the slot-coupled patch antenna.

You can assign different colors to different substrate layers. In the stackup manager, select and highlight the dielectric layer called "Patch Substrate" and click the Edit button of the dialog to open the substrate layer dialog. Click on the Color button to open Windows' standard color palette and choose green for the color of this layer.

Changing the layer color in the substrate layer dialog.

Once you return to the project workspace, your physical structure will look like this:

The geometry of the slot-coupled patch antenna with the virtual domain box showing substrate layers of different colors. The top patch object is shown in a mouse-over state.

The wizard created the following set of geometric objects, which together constitute your slot-coupled patch antenna structure:

Label Object Type Trace Group Length Width
ANCHOR Rectangle Strip PATCH_PEC patch_len patch_len
slot Rectangle Strip SLOT slot_wid slot_len
Open_stub Rectangle Strip FEED_PEC stub_len feed_wid
Feed Rectangle Strip FEED_PEC feed_len feed_wid

Running a PMOM Analysis of the Multilayer Antenna

The wizard already defined a scattering wave port called "WP_1" and associated it with the "Feed" object. It also initiated a default far-field radiation pattern observable as well as three current distribution observables, one for each trace group.

Attention icon.png In EM.Picasso, each individual trace plane requires its own current distribution observable. PEC traces have electric surface current distribution plots in A/m, while slot traces have magnetic surface current distribution plots in V/m.

The wizard also set the mesh density of the antenna structure to 30 cells/λeff as shown in the figure below:

The planar mesh of the multilayer slot-coupled patch antenna structure.

Run a quick single-frequency PMOM analysis of your multilayer planar structure. At the end of the simulation, the following port characteristic values are reported in the output message window:

S11: -0.684217 +0.056196j

S11(dB): -3.266925

Z11: 9.308750 +1.978907j

Y11: 0.102781 -0.021850j

Visualize all the three current distributions on the patch, slot and feed planes. Notice the standing wave pattern on the microstrip feed line.

The electric surface current distribution on the top patch.
The magnetic surface current distribution on the coupling slot.
The electric surface current distribution on the feed line and open stub.

Visualize the 3D radiation pattern of your antenna. Note the portion of the radiation pattern in the lower half-space (90° ≤ θ ≤ 180°).

The 3D radiation pattern of the slot-coupled patch antenna.

Tuning the Patch's Resonant Length

In this part of the tutorial lesson, you will vary the size of the top patch to find the resonant length. Open the variables dialog and change the definition of two variables: "patch_len" and "stub_len" to numeric values of "32" and "20", respectively. This change turns both of them into independent variables that can be designated as sweep variables.

The variables dialog showing the modified definition of several variables.

Now run a parametric sweep of the variable "patch_len" according to the table below:

Sweep Variable Name patch_len
Sweep Variable Type Uniform
Start Value 31mm
Stop Value 33mm
Step Value 0.2mm

Plot the data file "S11_Sweep.CPX". You can see that the return loss is minimized for a value pf patch_len between 31.6mm and 31.8mm. Open the variables dialog and set the value of "patch_len" equal to 31.7mm for the next part of the lesson.

The graph of return loss S11 as a function of the variable "patch_len".

Tuning the Length of the Open Microstrip Stub

The length of the open stub is usually set to extend λg/4 beyond the location of the coupling slot, where λg is the guide wavelength of the microstrip line. In this part of the tutorial lesson, you will perform a parametric sweep of the variable "sub_length". Note that you already fixed the value of "patch_len" at its optimal value of 31.7mm. Use the following parameters for the sweep variable "stub_len":

Sweep Variable Name stub_len
Sweep Variable Type Uniform
Start Value 20mm
Stop Value 24mm
Step Value 0.25mm

Plot the data file "S11_Sweep.CPX". You will find that the return loss is minimized for a value pf "stub_len" around 23.5mm. Open the variables dialog and set the value of "stub_len" equal to 23.5mm for the next part of the lesson.

The graph of return loss S11 as a function of the variable "stub_len".

Verifying Your Optimized Slot-Coupled Patch Antenna

At this point, your slot-coupled patch antenna structure must have all the optimal values of the design variables.

The variables dialog showing the optimal values of the design variables.

Run a single-frequency analysis of your antenna to verify its return loss and the quality of the current distribution maps. At the end of the simulation, the following port characteristic values are reported in the output message window:

S11: 0.029379 -0.009350j

S11(dB): -30.220259

Z11: 53.017276 -0.992318j

Y11: 0.018855 +0.000353j

Visualize all the three current distributions on the patch, slot and feed planes. You can see from the current distribution on the microstrip feed line that the standing wave pattern you saw earlier is gone. A more uniform current distribution on the feed line is now observed, which is an indication of a good impedance match.

The electric surface current distribution on the top patch in the optimized design.
The magnetic surface current distribution on the coupling slot in the optimized design.
The electric surface current distribution on the feed line and open stub in the optimized design.

Running a Frequency Sweep of the Optimized Slot-Coupled Patch Antenna

To examine the resonant behavior and bandwidth of your slot-coupled patch antenna, run an adaptive frequency sweep with the following parameters:

Start Frequency 2GHz
End Frequency 3GHz
Min. Number of Frequency Samples 5
Max. Number of Frequency Samples 15
Convergence Criterion 0.02

After the completion of the frequency sweep simulation, plot the data file "S11_RationalFit.CPX". The return loss (|S11|) graph has a minimum of about -32dB at 2.4GHz with a 10-dB bandwidth of about 35MHz.

The plot of the magnitude and phase of the S11 parameter of the optimized slot-coupled patch antenna.

 

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