Antenna Design using HFSS

Hi, this is Mark with Ozen Engineering and in this video we'll show how to use ANSYS HFSS for antenna simulation and design. We'll use this circular patch antenna as an example.

We'll walk through four basic steps to create the model and then review the different types of results which show us the performance of the antenna. So the first step is to create the antenna geometry. HFSS makes this very easy using a draw menu across the top.

We have a lot of different 1D, 2D, and 3D objects that we can draw and we have boolean operations that we can use to create different types of geometries. For the circular patch we've done that with the draw ellipse command.

You can click and see the history for this command and this model is fully parameterized so we can see the radius of the patch, the size of the patch, the substrate, and the location of the patch. We can also see the size of the patch, the substrate, and the location of the patch.

All of these objects have been parameterized and this allows us to optimize them and do parameter sweeps later on and look at our design performance.

So if we want to we can also go to the modeler menu and use the import feature and this will allow us to import different objects in many different formats such as STEP, IGES files. We can also connect HFSS into other programs to pull directly from CAD for example.

By doing a bi-directional link into SOLIDWORKS. So there's a variety of ways to create the geometry and set the model up creating the 2D objects.

Many times where antennas and conductors at high frequencies will use 2D objects and then for 3D objects like feed points, feed locations, and substrates we can use 3D objects built right into the interface of HFSS.

So our next step is to assign the material properties to our objects, and boundary conditions to our 2D surfaces. So the material library in HFSS is pretty exhaustive and if we'd like to add materials to the database we can also do that very easily.

You can see that we have some materials already assigned for the substrate material. We've assigned that to be one of the high frequency substrates. This material is shown in the library. It's built in already.

It has the permittivity or the conductivity and the loss tangent which are typically used in antenna simulations. You can also make these frequency dependent. You can make them spatially dependent or thermally dependent. You can apply different types of dependencies to the material properties.

You can make them anisotropic as well. The material properties are assigned to each of the 3D objects. Then we also have boundary conditions that are assigned to the 2D objects.

So if I look at the boundary conditions in the binder manager window, for the antenna, I have assigned a calculation to assess the finite conductivity boundary. And this has a conductivity of copper. We can assign a surface roughness model to that as well, if desired.

And for antenna models in particular, we can use different types of boundaries for the outermost boundary, in this case, the air box.

We can see in this case, we have got a radiation boundary that's been assigned to make sure that we have a reflectionless surface on the outside of the solution space. And so the next step is to define the ports for the antenna structure. And this is where the power enters the antenna.

And so in this example, we have a coaxial transmission line that's connected to the patch antenna. And we have a port called a wave port that is placed on the surface, the bottom face of this transmission line.

So if I look at that port definition, wave port is set up so that it will solve for the propagation constant, the characteristic impedance of that line. And then it will do a 2D field solution that is impressed on the full 3D electromagnetic domain.

So we can set up post-processing if we would like to renormalize that from the derived impedance, calculated impedance, to a standardized impedance, such as 50 ohms. It's very common to do when comparing to measurements. And also de-embedding the phase reference.

We can see the blue arrow, which shows us that we've de-embedded the phase up to the location where the transmission line stops. And then we can see that the voltage is at the point where the transmission line stops.

And then we can see that the voltage is at the point where the transmission line stops. So the last step in our setup is to specify our solution parameters. And this is under the analysis section of the project tree. So if we insert a solution, in this case, we would go to Add Solution Setup.

We've selected an advanced setup. And this is where we specify the solution adaptive frequency, and we can do that at a single frequency, or we can specify that to be done at multiple frequencies or across a bandwidth.

So in this case, we have a frequency setting of 11.6 gigahertz for the adaptive solution and a maximum of 12 passes with the maximum change in the S parameters set at 1.5%. And this means that the solution will automatically converge until this specified setting is reached.

So we can also set the adaptivity. So we can also set the adaptivity. And this means that the adaptivity will also change the adaptivity. So we can also set the adaptivity. And this means that the adaptivity will also change the adaptivity. So we can also set a frequency sweep.

We've got a couple of frequency sweeps here. To look at the frequency response of the antenna, we can use an interpolating frequency sweep, which will give us the S parameter solution. And in this model, it's set from 8 gigahertz to 15 gigahertz with 701 points.

And this will solve as many frequency points as needed to have the S parameter behavior converge across that frequency band. So this model took about two minutes to solve on a normal desktop computer. We can look at the results of this using solution data on the results ribbon.

If we look at the matrix data, we can see the S parameter for the single port. We can look at the convergence tab to see that it took nine passes, 41,000 mesh elements, and it reached the convergence criteria within nine passes.

So often, the first results to look at from your antenna model would be your S parameters, your input impedance. This is how well the antenna is working from the input side of the antenna, how well it's matched to the feed line.

We can plot results under the results section of the project manager project tree by right clicking and click on modal solution data report rectangular plot. We can create different reports based on the S parameters or VSWR. Look at the port impedance, propagation constants, and so forth.

So in this case, we've looked at for this model, we've plotted the return loss, which is the S11 parameter plotted versus frequency across the 8 to 15 gigahertz band. We see a nice resonance at 11.59 gigahertz. We can also plot that on a Smith chart.

So we can create a Smith chart as well very easily in HFSS and look at the impedance. And this will plot the normalized reflection coefficient.

And the center of the chart is the S 1. And this is the S 1. And this is the S 2. And this is the S 3. And this is on the S&I lip こ ki And this is the circuit. And the chart is where it's well matched. We can look at the input of our antenna. We can also look at the output of our antenna.

Define a radiation setup, which we can do and spherical coordinate system defining the desired parameters for the phi and theta angles. The resolution for how to look at those, we can produce 3D and 2D far-field plots. So this is the far-field plot of the antenna. You right click. You can click on.

show in modeler window. And if we double click on the model, we can see how the antenna is actually radiating into the far field. So we have the direction propagation along the plus z axis. So it's very useful for showing in presentations. We can right click and unselect show in modeler window.

We can see the gain value, 7.8 dB. And then we can look at 2D pattern cuts as well. So we can look at different elevation cuts, looking at phi equals 0 and phi equals 90 or other planes that cut through the peak of the pattern. So we can also look at the field behavior inside of the solution domain.

We are doing a finite element solution, so we have all the fields inside of the solution domain, in this case, which is inside of our airbox region. We can plot these under the field overlay section. If we have our coordinate system set up, we can plot on the global.

So we can plot the different planes for the, say, the custom coordinate systems, the different planes or different faces of the model. And so in this case, for this patch antenna, we've plotted along the yz plane, the electromagnetic field. So this is the electric field.

And it's showing us that the antenna is radiating on the edges of the patch. So we can see the edges of the patch. We can plot this in different scales. We get to the scale. Instead of a logarithmic view, we can plot this in different scales.

And again, we can see then it's really accentuating where the antenna radiation is coming from. So the circular patch is radiating from the outer edge of the patch. We can also animate this. If we right click and say Animate, we can select versus phase.

So we're looking at the time harmonic solution. We can animate this versus phase angle of the phasor solution. So we can see how the antenna is radiating into the far field. And we can also do this in the same way as we would in a linear model.

So we can see how the antenna is radiating into the far field. And we can see that the antenna is radiating into the far field.

So this is a very useful tool for antenna models that have complicated structures or, say, multiple elements, where we want to examine mutual coupling or interactions with the nearby environment. Well, that's all for this video. And thank you very much for watching.

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