And welcome!
And welcome to this Ansys video course
on designing
microwave passive components
using the Ansys Electronics Desktop
AEDT for short
and in this video we're going to discuss
how to analyze a T junction power divider
using Ansys HFSS in AEDT.
Before we proceed let us discuss
what a power divider is?
Power divider is commonly referred to as
a power splitter because it's used to
distribute the power of the signal input
to two or more outputs.
It can also be used to combine
two or more inputs to a single output.
It is a passive device
because it doesn't require any additional
source or excitation.
Now a power divider or combiner
it can be used with oscillators,
it can be used in an antenna feedback network
or arrays, radio measurements
and many other applications as well.
Power dividers are
available in many configurations.
The T junction power divider is
one of the types.
It has two microstrip arms
with an impedance of a hundred ohms.
There is one input port and two output ports
and the signal flows from the
input port to the output port.
At the junction where the signal is split
the signal is divided into equal
or some ratio depending on the application.
For example,
if you're feeding a uniform phased array
then you need an equal power division
If it's a non-uniform phase array then
you need an unequal split of the power
and there are many reference textbooks
on electromagnetic theory
or microwave components
and here's a textbook example
from one of these references.
A T junction power divider example problem
from the chapter
Power dividers and directional couplers
in the textbook
Microwave Engineering by David M. Pozar.
Now let's simulate the power divider
with unequal power division using
Ansys HFSS inside of AEDT.
If you're new to Ansys HFSS please watch
our other course Intro to Ansys HFSS
to learn more about the user interface
as well as geometry creation,
assigning boundaries and excitations.
So here is our model geometry.
For this model we use the default units
which is millimeters and in the history
tree window all the objects
of the simulation model are visible.
The top and the bottom conductors
are assigned to copper
and the widths of the
microstrip traces are designed for
characteristic impedance of 50 ohms
75 ohms and 150 ohms
at the frequency of 3.6 GHz
and based on the impedances the
power division would be about two to one
between the branches or the output arms.
FR4 epoxy is used as a substrate material
and the air space above the trace is
also assigned.
The microstrip line widths
were designed using the
transmission line model the TRL
wizard available inside of Ansys circuit.
We just showed how to use this TRL
wizard in the branchline quadrature hybrid video
part of this course.
Now the impedance of the microstrip
line depends on the substrate material
as well as its thickness
and to parameterize the substrate material
property for the dielectric permittivity
we'll need to use a project variable.
In the project manager window
go ahead and right mouse click on the
project name and select project variables.
In the properties dialog box click on add
another dialog box appears.
In the name field enter epsilon_r
and in the value put 4.4 click ok
and you can see a project variable is created
and note that a $ sign is prefixed
to the project variable name.
That's to differentiate a project variable
from a local design variable.
Click on ok to accept the changes
and go to the history tree window
under solids right mouse click on FR4 epoxy
for material and select properties.
The material property dialog box appears
and as you can see the relative permittivity
of the FR4 epoxy is given
as 4.4
and the manufacturing limits for
FR4 relative permittivity can vary from
say 3.3 to 4.8 pretty big
and this will affect your device output
performance and to see what this
material variation can affect
let's use simulation
a parametric simulation at that.
Go ahead and clone the existing
FR4 epoxy material by clicking on
clone material option
and that's the quickest way for you
to create a new material.
We can also add
a custom material by clicking on
add material option
and then edit all the
required material properties.
In both cases we will use the project variable
created earlier
to define the relative permittivity
of this new material.
For this video let's create the new material
by using the existing FR4 epoxy material.
In that pop-up box
enter
a new name some name to distinguish
it from the existing material
perhaps FR4_2.
Then in the relative permittivity cell
under the value enter
$epsilon_r
and click ok
and you see a custom material
with the given name is created.
Click ok to assign this to the model
and in the project manager window
expand excitations category and you see
one lumped port is assigned to each of the
arms of the power divider
and they are labeled for easy identification.
Double click on each of these ports to
see their properties.
Make sure that normalize impedance is
not checked.
Right mouse click on the excitation
category and select edit sources.
A new window pops up
and in this window we can excite
one of the ports by
using the magnitude and our phase field.
By default the input port is excited with
one volt of magnitude and zero phase.
Keep all other defaults and close the window.
Expand the analysis category and
double-click on setup1 to open the
solution setup dialog box.
The solution setup is defined with 3.6 GHz
as the solution frequency.
Expand the setup 1 and double click on sweep.
Interpolating sweep type is selected.
The frequency range is from 1 to 6 GHz
with 401 linear points.
Go ahead save the fields
by checking the check box.
Click ok to close the dialog box.
The analysis is all set.
So, let's go ahead and
validate the design before analysis
and after analysis is done
go ahead and view the results.
In the project manager window
right mouse click on the results category
select create terminal solution data report
rectangular plot
under the category select S parameters.
In that drop down menu go ahead
next to that select the quantity
only self terms
select all as shown.
Under function
select dB, select the new report, close
and here you see the reflection coefficient
at all the port.
You can also add X markers
to see the values at a
particular frequency
and similarly you can
just also plot the S parameters
from port 2 to 1
and from port 3 to 1.
You can also plot the characteristic
impedance of all the ports.
Once again
right mouse click on the results category
select create terminal solution data report
rectangular plot
and under the category select terminal port Z0.
Select the self terms for the quantity
and select all.
Click on the new report and close
and notice
all the port impedances are as defined.
Let's look at the field plots.
in the history tree window
select the top of the substrate
right mouse click
select the plot fields > E > MagE.
Keep all the defaults
in the next window and click on done.
and here's the magnitude of the electric field
on the surface of the FR4.
Let's go ahead and enhance
the color of the magnitude plot
by using the log scale.
Double click on the legend
select the scale tab and choose log
and click close to close the dialog box.
To animate the phase
right mouse click on the electric field plot
select animate and click ok
and here's the animation
showing the E field
splitting into the
two arms at the junction.
Go ahead close
the animation dialog box.
Now let's visualize the field interaction during
power coupling.
Go ahead do this by
editing the source
using the edit source option.
Change the magnitudes
on the ports as shown to combine the signals
from port 2 and 3.
Click on done
and you can see how the fields
for the ports 2 and 3 are summed up
and driven out to port 1.
Thank you for watching this video
on the T-junction setup
and in the next video we'll see
how to set up a parametric
for the substrate property
and also look at
another configuration of the T-junction
power divider with equal power division.
Thank you for watching this video
on the T-junction setup
for more information on our
Ansys electronic tools
or any of our Ansys simulation tools
please go to
ansys.com/courses today.
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