Continue to Site

Welcome to

Welcome to our site! is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

coax waveport size and airbox size for microstrip patch antenna in HFSS

Not open for further replies.


Full Member level 4
Oct 13, 2006
Reaction score
Trophy points
Activity points
I am simulating a patch antenna in HFSS with a probe feed. The probe is excited by waveport on a coax similar to the HFSS example. My coax height is just 2mm and radius is 1.6mm. Coax pin is 1mm radius. My bandwidth frequencies are 2-2.8 GHz. I am using the Driven Terminal solution. I am not sure if the size of the waveport radius of 1.6mm is correct. Is their a relationship between it and the impedance of the port? Also, I am renormalizing the port to 50 ohm impedance. What should the coax and waveport size be?

Also, the airbox size should be λ/4 away. Should it be λ/4 away from bottom or top of substrate? The HFSS example is from bottom, however the substrate thickness there is only 3mm. My substrate thickness is 15mm.

Also, I tried using a λ/2 away airbox and the S-parameter results are different. I even went to 1λ to see what results I will get, and they, too, where different.

Your help is sincerely appreciated.

If you have found the answer, kindly share the same.

Hi imkochar,

A driven modal solution setup should be used, the coax dimensions can be optimized by observing the return loss. The port should be a lumped port with a value of 50 Ohms, for an appropriate setup.

The air box (radiation boundary) needs to be lambda/4 away from the nearest radiating surface in order to work properly. Most likely in kae_jolie's case, the simulation was not adequately converged.

The coax dimension is required to deliver a characteristic impedance of 50 ohm. Refer to the characteristic-impedance formula of the coax.

Not open for further replies.

Part and Inventory Search

Welcome to