Antenna Matching using ANSYS Smith Chart Tool

Hello, this is Ibrahim Nassar with Ozen Engineering, and this demo will show you how to create a dynamic link between HFSS design and the circuit design, and how to use the circuit design with the Smith tool that is integrated to design a matching circuit, and then be able to push back the excitation into HFSS and see the impact of matching on the far-field data.

We will start this demo by having this antenna geometry, which is a log-periodic antenna that is designed to operate at 10 GHz and simulated from 8 to 11 GHz. Let's plot the S-parameters to see the data before the match.

So, let's create a rectangular plot of the S11, and as you see, the antenna is not matched, and we can also look at it in the Smith chart plot, and as you see, here is where the S-parameter is located in the Smith chart.

Let's also plot the far-field data to see how, after the match, the far-field data will be updated. So, let's create an antenna parameter report and select data table, and let's plot the peak directivity and the peak gain, the peak realized gain, and the peak system gain.

The reason I plotted all this quantity is because the peak gain is calculated based on the accepted power, so the mismatch loss does not impact the gain value.

The peak realized gain does include the mismatch loss, and the peak system gain gives you the gain of the total system when you have a dynamic link with a circuit. And this is basically the quantity that will be updated when we push back the excitation into HFSS. So, let's create the report.

So, we see that the peak gain is 5.37 dB, and because of the mismatch, the gain is lower by 2 dB, and we see also that the peak realized gain and peak system gain here - here, since it's the same power, input power is identical.

So, to create a circuit design, we can go to Project, Insert Circuit Design. Here, we can select the material definition if we want to have that, but in this case, we've just designed ideal matching circuit elements. So, let's keep it to none and hit OK.

So, now, in a circuit design is inserted, let's rename it to call it Antenna. Now, to link the HFSS design into circuit, we basically just drag it and drop it into circuit, and now, as you see, it will show up as a circuit component, and under the circuit design.

To simulate it, we can add the port, interface port, so let's click here, click here, and now we have a port. We can, in circuit, run linear network analysis. To do that, we can add an ExSim solution setup and linear network analysis, and here we can define a frequency sweep. So, let's hit OK.

So, it's already defined here from 8 to 11 GHz with a step of 0. 01. This is simulated by right-clicking on the linear frequency and clicking on Analyze. So, as you see, it's a quick simulation. Now, we can look at the parameters here.

So, by right-clicking on results and selecting create standard report rectangular plot S11 in dB. So, we see these results are identical to what we have seen in HFSS design, since both they use the same source of 50 ohm. Okay, so now, how do we match this antenna?

In the circuit, there is a Smith tool that we can use it here, or we can add just ideal circuit elements and run optimization and tuning manually. To use the Smith tool, we can go to circuit, Smith tool, and let's change first the frequency to 10 GHz, where we want to design the matching network.

Let's make this a little bit larger. Okay, the first step to design it is to add a data marker at 10 GHz. So, let's see where is the 10 GHz. Okay, okay, it's very close. Then, we right-click and say exit the marker mode.

So, now, we determined this is the point that we were trying to match to 50 ohms. So, to match it, we need to create a conjugate match. So, we would need to determine the conjugate point in the Smith tool before we add the matching elements.

To do that, we click on conjugate, and we select that data marker point. So, this is the matching conjugate match point in the Smith tool. Now, to design the matching element, we click on the matching tool. Now, we can right-click again and analyze the results and look at the Smith tool.

So, now, we see the antenna is nearly matched, so we can add a marker point and see where's the 10 GHz point now. So, the 10 GHz is almost at the center of the Smith chart. And we can also look at the rectangular plots, so we see now there's a good match at these points.

Okay, now, to be able to push the excitations, we need to modify the port. By double-clicking on the port here, we need to use a microwave port, and we need to edit this source by adding a power sinusoidal signal to this source.

So, we click here, and let's add one volt, and we keep all the other settings to be the same. Hit OK, and we hit OK, and we hit OK here. Now, we can re-simulate. Okay, so let's go back a little bit to HFSS, and to look at the added sources.

So, this is how the source magnitude and phase were defined in HFSS when we plotted the far-field data. So, now, we're going to push the excitation, to see the impact on the far field, we will see how the magnitude and phase are updated at the source. The system gain is 3.1 dB.

To push the excitation, select the circuit component, right-click, and select Push Excitation, and we will push the linear frequency data, and hit OK.

So, now, these results were pushed, so we go now into HFSS, we see if the sources got updated, so I click on Field Overlay, select Edit Sources, and now you see that the magnitude and phase are brought into HFSS design as a data set to have different magnitudes and phases over frequency.

And you see now, now that HFSS is automatically selected to use the system power, which is here in this case 0.0025, calculated from the circuit. And this box is checked to include the post-processing effect. So, hit OK. Now, we should see that the far-field data got updated.

So, now, you see that the system gain is now 5.357, which is very close to the peak gain. So, that indicates that the far-field data got updated, and the match got improved.

We can also notice here that the S-parameters did not change, because again, it's still calculated based on the analysis ran in HFSS. So, what only gets updated here in this dynamic link is the field quantities and the far-fields. That's all for this demo, and thank you for watching.

Thank you for following this video tutorial.