I do a lot of work in the sub-GHz ISM band and there are a lot of antenna vendors whose quality varies broadly. Consider the case of two antennae: The first was purchased from AliExpress vendor CS Family. These were sold as 915MHz antennae with 3dBi gain (this).

It’s centered at 910MHz and its best-case SWR is 1.34:1. At the band edges, it offers 1.57:1 at 902MHz and 1.77:1 at 928MHz. This is acceptable; I consider anything better than 2:1 acceptable for a cheap antenna and this meets its spec across the band. The impedance is 75 -j47. It’s not pretty, but it will do the job.

However, compare it to one of my favorite compact antennae from TE/Linx: the ANT-916-CW-HWR-RPS (datasheet) claims 1.2dBi and better than 2:1 VSWR.

This antenna is nicely centered in the band and offers an amazing 1:08 SWR at 915MHz, 1.57:1 at 902MHz and 1.40:1 at 928MHz. Impedance is 46.59 +j0.70. Now that’s pretty!

In fairness, both antennae meet their spec (better than 2:1) and the AliExpress antenna cost only $2.16 whereas the Linx antenna cost $13.50…so I cut the AliExpress guys some slack 🙂

Measurements taken using a NanoVNA SAA-2N with VNA Qt software. I might break out a nicer VNA some time and repeat these tests, but for quick measurements, I’ve found the NanoVNA2 to be remarkably accurate; it’s insane what $110 can buy these days. Note: if you have a NanoVNA2 SAA-2N, the firmware, manual, schematic, and a version of VNA Qt that works with it can be found here. The 1.3.07 firmware (Aug 30, 2022) offers many important features and if you’re running older firmware, you probably want to update (instructions are in the manual). The only thing I couldn’t find a way to do using the LCD UI was port extension, but it’s easy with VNA Qt.