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Where To Find This Example

AWR Version 14

Understanding AWR .emz Files

AWR Version 13

Understanding AWR .emz Files

Design Notes

Patch Antenna on Finite Substrate

Download

Simulating this project is time-consuming.  This example, with the datasets included, is available at:  http://kb.awr.com/display/Examples/Patch_Antenna_Finite_Substrate

Overview

This project demonstrates how to model a patch antenna on a finite substrate. Because the finite substrate is not an infinite planar structure, this structure can only be modeled using a 3D EM simulator such as Analyst. Furthermore, the effect of substrate size on antenna performance is examined.

Parameterized EM Layout

Edge Length modifiers are placed on the shapes representing the finite ground plane and finite dielectric in order to parameterize substrate size. In this example, the amount the substrate extends beyond the antenna edge is parameterized as a multiple (n) of substrate height (h).  A SWPVAR element is used in the EM Schematic to sweep the value of n, so the effects of a 2*h, 5*h, and 8*h substrate extension are compared.  The geometry for each sweep can be inspected by right click on “Patch” and selecting Preview Geometry.

Stackup

The antenna is modeled in the EM structure “Patch”.  This structure is defined with a three EM layers in the Stackup.  The height of the middle layer is set equal to the height of the substrate. The height of the bottom and top air layers are set large enough so that the boundary does not interact with the antenna. 

The substrate is modeled with a finite dielectric shape.  Finite dielectrics are created in the same manner as conductor shapes.  For this structure, a dielectric Material Definition “diel1” is added with corresponding Er and Tand.  This Material Definition is mapped to a Material “Sub1” with thickness h = 60 (mils).  Now that “Sub1” is defined, it can be associated with a Drawing Layer on the EM Layer Mapping table.  In this example, “Sub1” is associated with the Drawing Layer “Board”, which is mapped to EM layer 3 in the stackup.

In the EM Layout, any shape drawn on layer “Board” defines a finite dielectric region.  In a similar manner, the finite ground plane is defined by shapes drawn on “Copper_Gnd” layer.

Boundary Conditions

Because the antenna structure is symmetrical, an Electrical Symmetry boundary is used to reduce the computational problem size by half. Only half of the structure is drawn, and the Electrical Symmetry boundary is placed on the plane of symmetry. Symmetry Boundaries can only be used in cases where ports are bisected by the plane of symmetry. 

When modeling an antenna, all radiating boundaries must be defined with the Perfectly Matched Layer (PML) boundary condition. The PML boundary should be placed at least a quarter-wavelength away from the antenna. In this example, all boundaries except for the Symmetry boundary is defined as a PML.

More details about Boundary Conditions can be found by clicking on the HELP button in the Boundary Conditions properties window.

Measurements

The graphs in this project show the effects of increasing substrate extension from 2*h to 8*h on antenna input impedance, real and imaginary, and return loss. 

The effects of the different dielectric sizes can also be seen when looking at the antenna's radiation pattern.  This includes the main lobe beam width, the co-polarized field and the cross polarized field in both the E Plane and the H Plane.  By default the co-polarized and cross polarized fields in the E Plane and H Plane are set to plot a single sweep of the dielectric brick, n = 8.  To view these measurements at different dielectric brick sized double click on the measurement to open the Modify Measurement dialog box.  Then change the value of SWPVAR.SWP1 to the desired setting in the measurement dialog.

EM Structure - Patch

EM Structure 3D - Patch

Graph - Input Impedance Real

Graph - Beam Width

Graph - Input Return Loss