When measured and simulated results do not match?

Most engineers at some stage get that sinking feeling when their measured and simulated data do not match, especially after they’ve tried and tested everything to find the root of the problem. Some engineers just give up and write off the discrepancies due to cable/connector loss or some phase shift that is not accounted for in the simulation.

One of our engineers recently had a similar occurrence with the validation of the Yagi-Uda Monopole Array with Folded Feed antenna soon to be implemented in the Antenna Magus database. He manufactured the reference design in order to have a trusted measurement to use in the validation process. Unfortunately the impedance measurements and simulated results had some differences especially around the resonant frequency. After examining and comparing the parameters of the manufactured antenna with the simulation model using a vernier he found that the brazing rods weren’t exactly 3.2mm as specified and the thickness varied as well. Not expecting these differences to have a huge effect, the simulation model was modified to take these into account and surprisingly the new simulated results almost matched the measurements. Later one of the other engineers confessed that the rods fell off his motorcycle three times on his way back to the office.

So next time before blaming the computer or the network analyser have a closer look at the built model – you might be simulating something that doesn’t exist.

Simulation model and manufactured model of the antenna before any modifications.

Simulation model (a) and manufactured model (b) of the Monopole Yagi with folded feed array antenna before any modifications.

Comparison of S11 for measured vs original and new simulated results.

Comparison of S11 for the measured vs old and new simulation models.

Author: Robert Kellerman

Leave a Reply

Your email address will not be published. Required fields are marked *