And are the assumptions on the substrate (1.5mm FR4) correct for this example? The link to the PDF is broken.
paper:
**broken link removed**
lufer17 uses CST MWS, and his youtube video shows that software somehow calculated port impedance of 115.7 Ohms. And all confusion comes from the fact that port impedance is not set manually.
I took dimensions from paper and run some simulations, here is the result:
View attachment 157955
red curve: 60 Ohm lumped port - 60 Ohm transmission line - circular patch
blue curve: 115 Ohm lumped port - 60 Ohm transmission line - circular patch
both S11 looks well because antenna is very wideband, and with 115Ohm port impedance is "swirling" on the left part, crossing 115 Ohm point several times.
Maybe CST MWS took impedance from center frequency, and used real part as port impedance.
To obtain results similar to the paper port impedance must be manually set to 62 Ohm, or maybe:
1. Use 2.9mm wide line (50 Ohm)
2. Manually set port impedance to 50 Ohm
3. Add quarterwave transformer or linear taper to transform 50 Ohm (2.9mm) to 62 Ohm (2mm)