Overview
This blog shows how to use the ANSYS circuit smith tool to match an antenna designed and simulated with HFSS 3D. ANSYS HFSS designs can be dynamically linked into ANSYS circuit tool to accelerate the design process and increase the design flow power and flexibility. Below is a brief illustration of the workflow and a full demonstration is provided in the video link.
1) HFSS 3D simulation of the antenna
In this example we will simulate a log periodic antenna in HFSS 3D and plot s-parameters and far fields.
The below figure shows the initial simulation of the s-parameters before any matching is introduced and the below table shows the antenna Directivity, gain, Realized gain, and system gain. The realized gain and system gain shows a ~2.1 dB mismatch loss.
2) Dynamic link with Circuit
In ANSYS Electronic Desktop (AEDT) we can add a circuit design and link the HFSS design to it. The HFSS antenna design can also be linked into a schematic from a different project. To link the HFSS design into circuit, we can drag and drop the HFSS design into the circuit design and then the HFSS design will be a component in the circuit design. This link enables the users to add circuit element including active circuitry and run different types of analyses.
To simulate the antenna, a microwave port should be added with a sinusoidal AC source.
To perform linear network analyses, the user can add Nexxim Solution Setup and define a frequency sweep.
The S parameters can be plotted as seen below. This results is identical to the S-parameter plot created in HFSS Design. In this case, we are exciting the HFSS design using a 50 ohm port, which is the same impedance as the port used in HFSS.
3) Using the smith tool
To start the smith tool, select menu item Circuit >> Smith Tool
To start the matching process, we first add a marker at the frequency point of interest which is in this case 10 GHz. To match the 50 ohm source to this marker point, click on conjugate to determine the conjugate point on the smith tool.
After the conjugate point is determined, we can start the matching. In this example, the antenna is matched to 50 ohm source with a series capacitor and a shunt inductor.
The below figure shows the matching sub circuit that we inserted.
After the matching circuit is inserted we can re simulate and see the updated S parameter plot. As seen below, the 50 ohm match point right at 10 GHz.
3) Push excitation
To see the impact of matching on the far field data and obtain a realistic far field results based on the actual magnitudes and phases presented to the antenna input port, we can push the excitation from the circuit design to the HFSS design. This step will update the HFSS source magnitude and phase information, as seen below.
With the improved matching at 10 GHz, more energy is accepted by the antenna from the port, and stronger electric field can be radiated. Looking at the updated far field data below, we can see that the system gain is now very similar to the peak gain.
Similarly, we can see that the system efficiency is very similar to the radiation efficiency at 10 GHz
Definitions:
Peak Gain: Gain is 4π times the ratio of an antenna's radiation intensity in a given direction to the total
power accepted by the antenna.
Peak Realized Gain: Realized gain is 4π times the ratio of an antenna's radiation intensity in a given direction to the total power incident upon the antenna port(s).
Peal System Gain: System gain is 4π times the ratio of an antenna's radiation intensity in a given direction to the user specified power.
Radiation Efficiency: is the ratio of the radiated power to the accepted power.
Total Efficiency: is Radiated Power over Incident Power.
System Efficiency: is Radiated Power over System Power.
A complete demonstration is provided in the video link below: