Realized Gain greater than Gain in HFSS. How is it possible?

gcaricatogcaricato Member
edited December 2020 in Electronics

Hi all,

I'm simulating a printed meandered dipole working at ETSI UHF Rfid band in HFSS 2019 R1. I noticed a strange thing: for some frequencies I got a Realized Gain greater than Gain (both evaluated in dB and for same Theta and Phi). I'll show you some plots to be more clear.

This is S(1,1) plot.

This is Gain and Realized Gain VS Frequency plot at Theta=Phi=90°.

This is Gain and Realized Gain VS Theta at Freq=867MHz and Phi=90°.

Can someone explain how this is possible? I'll give you more infos if needed.


  • VivekKVivekK Pune, IndiaForum Coordinator

    Hello @gcaricato,

    Please understand HFSS calculates realized gain and peak gain with a different formula, Please refer HFSS help document to get a better understanding.

    Gain and realized gain are very close to each other when the antenna is matched. However, for designs with a multi-port antenna, gain and realized gain can be different if incident and accepted power are different. There can be a small reflection at the ports and accepted power may still be small if energy injected in one port exits the model through a different port. A review of the S-matrix can show this to be the case. This does not happen in a single port antenna, which is what most users base their expectations on. When global material environment is a lossy material, antenna parameters such as gain and radiated power are no longer unique because the radiated power depends on the location of the radiation surface since power is lost as the wave travels in the background material.

    I am attaching some screenshots from the help document for your reference.

    I hope this will help to resolve your concern



  • Hi @VivekK, thanks for reply. Sure, I'm aware of the differences between Realized Gain and Gain and that's why I created this discussion, A Realized Gain higher than Gain is physically meaningless. So I was wondering why I got these results, if there is something wrong with my approach to simulation. Discussing the problem with other users, I realized that probably this strange behavior is due to the use of Lumped Port with complex impedance. Indeed, I'm simulating a printed meandered dipole working at ETSI UHF RFID band and I am using a Lumped Port with impedance 23.3+i*145, this to obtain a conjugate impedance matching (chip's impedance is 23.3-i*145). I see this approach is the most popular for simulating RFID antennas (at least, that's what I learned from documetations and scientific papers).


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