- Thu Apr 02, 2015 2:19 pm
#13298
I just went through this for the design of my Arachnio (obligatory plug: now on Kickstarter
https://www.kickstarter.com/projects/lo ... o/arachnio), and it worked out pretty well.
This is extra-easy for the ESP8266, since the antenna pin is a single-ended 50 ohm line. Therefore, the only matching network you really need is a single blocking cap of 5.6 pF. Make sure it's an RF capacitor with a self-resonant frequency well above 2.4 GHz. It will cost more than you are used to paying for a chip capacitor, but not too much.
The cheapest way to do the antenna (at least on a per board basis -- this is more work) is to slavishly copy someone else's printed antenna design. This is what I did for the Arachnio. If you have a microscope set up for measuring or a set of gerbers, you could directly copy the antenna from an existing ESP module. They mostly seem to be pretty good. Another possibility is copying one of the designs from another company's app note. Both TI and Freescale have published excellent app notes discussing different antenna designs. If you use them, treat all dimensions as critical, especially ground spacing and PCB thickness/material and copper weight. Those things really do matter to get the antenna performance the designer intended.
If you are willing to spend more money per board in exchange for doing less work, there are a variety of chip antennas available. My favorite by far is this one from Molex (
http://www.digikey.com/product-detail/e ... ND/2683663), because it's got relatively good performance and is admirably unfussy about where it's installed, so it gives you lots of design flexibility. It also costs almost as much as the ESP8266 itself does, so you may not want it. Regular chip antennas tend to be a little bit fussy about how they are installed. Read the manufacturer's data sheets and app notes and unless you are experienced with antenna design, follow them without question.
