Simple Antenna Makes For Better ESP32-C3 WiFi

We’ve seen tons of projects lately using the ESP32-C3, and for good reason. The microcontroller has a lot to offer, and the current crop of tiny dev boards sporting it make adding a lot of compute power to even the smallest projects dead easy. Not so nice, though, is the poor WiFi performance of some of these boards, which [Peter Neufeld] addresses with this quick and easy antenna.

There are currently a lot of variations of the ESP32-C3 out there, sometimes available for a buck a piece from the usual suspects. Designs vary, but a lot of them seem to sport a CA-C03 ceramic chip antenna at one end of the board to save space. Unfortunately, the lack of free space around the antenna makes for poor RF performance. [Peter]’s solution is a simple antenna made from a 31-mm length of silver wire. One end of the wire is formed into a loop by wrapping it around a 5-mm drill bit and bending it perpendicular to the remaining tail. The loop is then opened up a bit so it can bridge the length of the ceramic chip antenna and then soldered across it. That’s all it takes to vastly improve performance as measured by [Peter]’s custom RSSI logger — anywhere from 6 to 10 dBm better. You don’t even need to remove the OEM antenna.

The video below, by [Circuit Helper], picks up on [Peter]’s work and puts several antenna variants to further testing. He gets similarly dramatic results, with 20 dBm improvement in some cases. He does note that the size of the antenna can be a detriment to a project that needs a really compact MCU and tries coiling up the antenna, with limited success. He also did a little testing to come up with an optimal length of 34 mm for the main element of the antenna.

There seems to be a lot of room for experimentation here. We wonder how mounting the antenna with the loop perpendicular to the board and the main element sticking out lengthwise would work. We’d love to hear about your experiments, so make sure to ping us with your findings.

21 thoughts on “Simple Antenna Makes For Better ESP32-C3 WiFi

    1. The way I understand it, yes. If you remember the old PCB antennas, they would be as far isolated from the main PCB as the SMD antenna in the first board example. The same conclusion the article arrives at. The “minified at any cost” boards are simply “too busy”.

      1. I worked for a testlab and the funny thing was we discovered at one time that the actual “antenna” was an ordinary zero-ohm resistor. Turned out that in the aplication note the recommended layout was the real antenna. Nice upcharge from 0.1 cents to a couple of bucks selling these.

  1. Is it legal though? In most countries, you don’t need to have a radio operator license to operate and buy these kind of modules because they’re pre-tested for EMI compliance, radio spectrum and transmission power limits. If you modify them, they’re no longer in spec and you can fall foul with whatever radio regulations you have.

    1. The ones from AliExpress with the faulty antenna are not the tested compliant units you’re thinking off.

      Ordering these unknown parts from AliExpress makes you the importer and responsible for ensuring compliance.

    2. The low price super mini is not approved.
      There is a version of super mini with CE FCC with shield can and the seperate flex antenna much like the regular wrover module.

      Cost $23 typically

    3. You can always certify yourself ($$$), but in the US, to have the benefit of modular approval, you should only use the ones with a metallic shield (if you want to sell these products.)
      For the EU you have to stick to the certified antenna gain to reuse module reports, otherwise you again need to certify yourself.

      I do not understand why they keep the original antenna on. If you are going to use a quarter wave antenna, better just remove the original completely. The extra loop is not really needed, but is good for mechanical support and ESD protection, also filters some of the low-band spurious products.
      Also claims of incredible gains should always be taken with a grain of salt. Although you can loose a couple of dB’s with wrong placement, you really have to try hard loosing 10 dB. In the end it is mainly mismatch loss that causes loss of energy.
      The actual gain(directivity) of the antenna can also not be increased with a small antenna. To achieve gain you need a physically large antenna. And even then, antenna gain is only beneficial is one specific direction. All other directions will have lower performance. Think of it as a balloon. If you squeeze it in one direction, other directions will increase. It all boils down to conservation of energy. In specific these chip antenna’s are optimized to show isotropic performance. At least better than a dipole.

      1. The point is that the SMD antennas on these mini boards are not positioned according to the datasheet. The mismatch is so significant that it causes the chip to heat up.
        The new antenna wire forms a quarter-wave antenna, with the loop and straight part ensuring an omnidirectional radiation pattern. The original blog post is cautious about claiming gains of more than 6 dB, but the measured improvement compares a modified module to an original one mounted next to each other, both connected to a distant access point at the same time.

  2. I didn’t spend a whole 22mins of my life on that talking head video, but it appears that he would benefit from learning a little bit of antenna theory and practice. Capacitive and inductive loaded antennas are always interesting.

    I’d look at either any of the ARRL yearbooks, or at Thomas Lee’s Planar Microwave Engineering. The latter has a similar flavour to TAoE, including some delightfully droll observations.

    1. In fact 20 dBm would sounds more believable, based on nominal 20 dBm output power (100 mW), than 20 dBm more (+100 mW) would in fact be 3 dB more (2 x). It is way more believable than 20 dB more (100x).
      Besides that, I would not be surprised that a this difference in power is due to polarization effects. The polarization is also rotated 90 degrees.

    1. 34 or 31 mm is all the same for the antenna radiating performance itself. The main thing is that you tweak the mismatch loss/VSWR interaction. (absolute gain vs realized gain). By making the antenna slightly shorter/longer it becomes slightly more inductive/capacitive, compensating the output impedance of the board. Also the antenna does not have a well defined groundplane, so will not be perfectly 75 ohms. I did not look it up, but the output impedance is probably more like 50 ohms.

  3. does xaio esp32 os use debian?

    AI Overview.

    No, the XIAO ESP32 (and other ESP32-based boards) do not use Debian
    as their operating system. They typically run a real-time operating system (RTOS)
    called ESP-IDF (Espressif IoT Development Framework).

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