Proof I'm not an RF engineer

Back in 2013 I did a project with a Nordic Semiconductor nRF24LE1 chip. This is an 8051 compatible microprocessor with a built-in 2.4 GHz wireless transceiver. Conscious of how poor my knowledge of RF design is I followed the sample layout of the RF section exactly for the antenna. And by "exactly", I mean I overlaid the sample Gerber file onto my PCB layout and used that to position the components and route tracks. Without the proper tools to tune an inverted-F antenna like on the original, I used a commercial 2.45 GHz chip antenna with a 50 ohm impedance.

Everything seemed to work exactly as designed except the RF section. I could not get the board to talk to a commercial board using the same nRF24LE1 chip. Clearly I'd botched something.

I called a friend who is an Extra-class amateur radio operator and asked his advice. He reviewed my choice of passive components in the RF section and had me change out a couple which he deemed inappropriate for use at 2.45 GHz. This made them work when talking to each other, but they still wouldn't talk to the commercial boards and had significantly reduced range. Without the test equipment necessary to look at a 2.45 GHz signal, the project got shelved.

With the advent of inexpensive spectrum analyzers like the TinySA, and vector network analyzers like the NanoVNA, it's now possible for me to dig into this without spending thousands of dollars. There's no practical reason for me to do this, as the original purpose of this project is years past. But I hate unresolved questions.

While I learn to use my new toys... err... tools, I took another look at the board layout. The feed to the antenna is supposed to have a 50 ohm characteristic impedance. This board is 1.0 mm thick FR4, with a solid ground plane on the bottom excluding the area where the chip antenna is mounted. The calculator I used said a microstrip transmission line should have a width of 73 mils (1.85 mm), so that's what I used.

Now I realize that this configuration isn't a microstrip, it's a coplanar waveguide with a ground plane, which requires a completely different calculation. Plugging in a 73 mil trace and 7 mil spacing to the ground fills on the top, I get about 36 ohm impedance. Oops.

This seems bad, but the trace is only about 100 mils (2.54 mm) long, a tiny fraction of the 4.8 inch (122 mm) wavelength of this signal. Is this impedance mismatch enough to cause serious problems, or is there something else wrong? Perhaps there are other components in the matching network that are unhappy at 2.45 GHz?

I think what I'm going to do is build a test board like the one described by the antenna manufacturer in the chip antenna's data sheet. That will let me experiment with my VNA and something that should have known characteristics. This should help me understand if I'm reading the indications correctly.