PCB antenna - TI's DN038

SWRA416 | 2020-09-02, 04:13:00

In my earlier post, I talked about the transmission module without describing the on-board antenna.

I've copied this antenna at almost 1:1 scale from Texas Instruments' design note 38 (which they used to provide as a standalone gerber file *somewhere* on their website).

The conversion from gerber coordinates to object wasn't even near usable, a lot of lines need to be deleted, redrawn, realigned and the holes to be placed.

I simply assumed it wouldn't even work and, ironically, this is the third design or so that I've told myself that 'I'd test it' and I've expertly forgotten the impedance matching network it needs. So this time I've put this exact info in the description of the antenna in my library.

The DN038 antenna is really small, which makes it perfect for small boards (I think one of almost the same size goes inside a lot of remotes).

Well, without the matching impedance network it's kind of useless, but it works! Worst case would have been not working at all.

I've got -72dBm (self-reported by SX1276) by pointing two boards at each other at 30 cm, which is rather disappointing but the antenna isn't matched! Most of the power is wasted as reflections and heat.

Then I had the idea to use the dipole antenna as the transmitter (since the helical should be able to receive it) and I've got -49 dBm (self-reported) at the same distance (and I get between -20 and -30 for two dipole antennae at 30 cm distance) -- so I'm going to assume it has to do a lot with orientation, line of sight... maybe even the ground around the antenna.

Give it a try! The matching network is a 1pF capacitor in series with the transmission line and a 12nH inductor shunt placed in-between the capacitor and the antenna entry point. Make the path as short as possible (not like in my designs).

My library also includes the TI helical antenna for 433Mhz and the DN024 monopole.


Categories: antennae

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