The mismatch between the Circuit and HFSS Model

[qiank10]

Hello,

I want to design the reconfigurable reflect patch antenna with a diode controlling the impedance of the transmission line. So I try to simulate the impedance of the stub, as shown in the following figure:

The corresponding circuit model is:

However, they give very different simulation results.
Below is the phase of the S11 vs. the length of the second part of the transmission line:

Attached please find the Ansys project.
Do I miss some factors in the circuit simulation? Is there any way to identify the cause?

Thank you!

 

[PlanarMetamaterials]

Welcome, qiank10.

It's a bit hard to evaluate your proposed model without knowing what it is you are trying to do, but there seem to be a few discrepancies. The parallel RC tank you have in the HFSS simulation is connected to your ground plane, whereas you are not modelling this with your circuit. The two line lengths of 1mm do not seem correct given the HFSS setup which has two sections of 1mm and 2mm.

 

[BigBoss]

That Equivalent Circuit cannot represent an Antenna since you don't know the Boundary Conditions.
In additional to this, an Antenna is pretty complex structure and there are many factors that influence its equivalent electrical circuit such as Radiation, Polarization,Scattering, etc.Simplified solutions will not work.
Therefore we simulate the Antennas in EM 3D Simulators.

 

[qiank10]

Welcome, qiank10.

It's a bit hard to evaluate your proposed model without knowing what it is you are trying to do, but there seem to be a few discrepancies. The parallel RC tank you have in the HFSS simulation is connected to your ground plane, whereas you are not modelling this with your circuit. The two line lengths of 1mm do not seem correct given the HFSS setup which has two sections of 1mm and 2mm.

Hi PlanarMetamaterials:

Thank you!

I read a paper titled "60-GHz Electrically Reconfigurable Reflectarray Using p-i-n Diode" and want to adapt their reflect patch antenna to 28 GHz:

I tried to model the patch and the stub separately and the HFSS project is for the stub part. It consists of a line, a diode represented by two lumped RLC, a second line, and a lumped RLC representing the via. The last lumped RLC connects the ground plane and is set to have an inductance of 75 pH, which equals the inductance of the last inductor in the circuit project.

The 2nd line in both the HFSS and the circuit project is parameterized and has the same range from 0.1 mm to 2.5 mm.

 

[qiank10]

That Equivalent Circuit cannot represent an Antenna since you don't know the Boundary Conditions.
In additional to this, an Antenna is pretty complex structure and there are many factors that influence its equivalent electrical circuit such as Radiation, Polarization,Scattering, etc.Simplified solutions will not work.
Therefore we simulate the Antennas in EM 3D Simulators.

Hi BigBoss,

Thank you for your reply.

I'd like to find an approximate model to get an initial estimation of the parameters for this design, e.g., the length and width of the lines, the inset length of the patch. Then, I can search around the initial estimation to fine-tuning the parameters. But since there is a large difference between the circuit model and the HFSS model, I guess I have to search through the whole parametric space.