I have a question. Imagine that I need to have a 50 ohms impedance in a PCB trace. For simple cases it's just applying the formula found all over the internet or use one of the online calculators
While looking for this information online I came across an article where a guy created a low cost electric field probe and a low cost magnetic field probe and then proceeded to perform tests on different configurations of microstrips on a dual layer board. His goal was just that, measure magnetic field and electric field with a near-field probe, with a low cost set up, so that small companies can perform their own tests before spending lots of money certifying the end product.
The configurations were as follows:
- L-shape: One side all ground, not corroded. The other side just had a line trace in the shape of an L.
- H-shape: One side all ground, not corroded. The other side had traces forming an H, and the middle of the H had a line going to the edge of the board (the other traces, parallel with this one didn't go to the edge of the board).
- Radius-shape: This one was one sided.ç It was connected to the edge of the board on one side, it made a loop and the end connector was just beside the entry point.
It was necessary for the measures that the impedance on those lines were 50ohms. I honestly can't see how he calculated the impedance for those odd shapes, and I can't find any material on the web concerning how he was able to assure 50ohms on those lines.
Can someone point me in the right direction?
Did he just add termination resistors in specific places? Maybe in the H-shaped one he simply added 4 200 ohms resistors one each of the "legs" of the H? Does this guarantee 50 ohms? Then how did he do it to the radius-shaped one?
Original article: Analysis of Electromagnetic Emission from PCB by using a Near-Field Probe