The lumped port sheet seems somewhat... suboptimal. I would copy the whole structure, intersect it with a centered circle and then connect all the new corners by line elements and finally close the line.
Yes. I don't think your lumped port was completely unusable, but it should only be connected at two edges and yours touched the spiral on the side as well.
Yes, draw a circle, centered at the origin, so that when you intersect it with your antenna (which you of course copy before intersecting) gives you four corners, on which you can nicely draw a rectangle by just using the straight line tool and closing the line.
Okay, here's the fixed version of your RHP spiral - I only fixed the port, the total performance remained unfavorable. I don't think, it is so easy as just to subtract the normal log spiral from a rectangle and use it again as broadband antenna... otherwise, there would not be a Babinet's Principle.
Hmm... how did you feed it then, in the real case? And is the PCB thickness and material the same? How about the measurement environment - was the antenna really measured without any ground?
I think, there has to be a dominant discrepancy between your HFSS model an the real case... For example, I found that, when I build the test antenna with an SMA connector, I also have to include that in the model, at least in the last step.
So, there are quite a few differences between the model and the reality...
- How far away is the ground in practice? Generally, ground planes have a huge impact on the overall impedance and efficiency (since then generally most of the electric field is in between the antenna structure and the ground plane).
- If you use FR4 in practice, there really is no reason why you would use Rogers in HFSS.
- You can always use a SMA connector model to feed your antenna, if that's what you do in practice (I didn't quite get that from your description): draw two cylinders, one being the inner conductor with a radius of typically 0.65mm (1.3mm diameter is used by most SMA connectors like H&S, etc., but use the one you actually have, of course) and the outer cylinder with radius rInner*exp(5/6*sqrt(eps)) where eps is the relative permittivity of the isolation material of your connector (usually Teflon, eps=2.1). The inner cylinder of course should be PEC or copper, while the outer is made of the isolation material (Teflon). Subtract the inner from the outer (check the copying box). At one end the inner conductor should reach out to the structure you want to feed and at the other you apply a full solid PEC cylinder of the same radius as your isolation cylinder, with a thickness of, lets say 1mm. The whole connector sould be 3-5mm long. Press the "F" on the keyboard and mark the lateral surface of the isolation cylinder and apply PerfE boundary. Mark the inner top surface of the PEC end cylinder (or the adjoint surface of the isolation cylinder, with a whole in the middle) and apply a waveport excitation with the integral line reaching from the inner straight to the outer radius. You can use the deembed-function and deembed the whole connector length (the 3-5mm), to get zero phase offset.
I use the coax connector most of the time and got very good agreement with practice in general.
Do what? As you can imagine, I actually have to work and most certainly can not / won't do the work for you!
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