Simulation question in EM mode for antenna

I just want to simulate an RFID antenna to compare with real one measured by VNA. Layout, which follows the real one sample, just like following with 2 ports. And due to de-embedding issue, these two ports can only setup as Internal Mode.

The result of this antenna is like following, it has huge difference between real sample.

The peak frequency should around 900MHz rather than over 1.1GHz.

Is anyone could give me a hint why I get this difference, I know it might have something wrong for my setup.

I try to modify the dimension slightly or offset for port 1/2, but it turn out same result, over 1.1GHz.

Here are some setup details as following,

I try to place port2 on the edge of conductor, but it shows an error msg, "port cannot be defined as partially on the perimeter of structure partially inside the structure.".

I'm confused by your design.

Do you really have this feed and radiator over a solid backside metalization, as modelled in your Momentum substrate?

What does your feed in hardware look like? Is that really two ports with reference at backside ground, or one port between these two points?

Hi volker_muehlhaus,

Base on your reply, it seems this simulation has two main problem, quantity of ports and position of feed.

1. The real case is that there is an IC chip between port 1 and port 2, so I placed two ports. But I wonder whether I should place each port if there is an "connection" from outside.

2. I had found that these two ports coming from backside through 3D viewing, it looks wired. And I tried to change the position of source, but the result keep same, sources are coming from backside. Does this would affect the result?

Thanks,

Hello,

unfortunately the answer "there is an IC chip between port 1 and port 2" does not tell us if the IC has two single ended outputs (Momentum: two ports to ground) or one differential output (Momentum: one differential port). That is a major difference.

Also, you have not answered by question on the backside ground which you have in Momentum, but does it exist in reality? This is a really strange structure, is it copied some some 3rd party design (but copied with mistakes)?

Hello Volker,

1. IC output are R+ and R-, so I think it should be two differential ports? I try to setup these two ports with diff mode, one is normal and one with reversed. But it shows error message while I setting associate port, like following picture. And the following link is the setup steps I was followed.

http://literature.cdn.keysight.com/litweb/pdf/ads2008/mom/ads2008/Ports_in_Momentum.html%23PortsinMomentum-1104695:Ports in Momentum

2. Actually, I would like to verify my simulation is correct before I make further research. Therefore, I bought some RFID test samples with RF-4 PCB on backside. Normally, it should apply polyester membrane or something similar material. But this is a test sample, I think seller place the antenna on RF-4 to make buyer easier to connect to SMA connector. I am not sure whether this is an existing antenna, but according to my measurement , it shows correct performance.

And I followed some instruction from internet to setup my substrate, please tell me if I am wrong.

Thanks for your help,

附图/附件

diff mode setup_1.png

Yes, this looks like one differential port. You are using a very old version of ADS, so I don't remember how differential ports are created there, but you need a differential port.

Regarding your antenna, if it works in hardware (measurement) that's fine of course. I never saw such a setup before.

Good luck!

Volker

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