Can I use a 2.4 GHz antenna for 900 MHz signal?

Question

I have a 900MHz LoRa device that I want to attach a more directional antenna to. I have a 2.4GHz corner reflector sitting around. I was wondering if I can replace the current omnidirectional antenna with this one.

Is it safe to do so? I read in LoRa documentation that running without an antenna can damage the equipment.

Also I heard of something called impedance mismatch but can not determine if that affects me or not in this case.

If I replace the antenna do you expect that I see a performance improvement given the antenna is rated for 2.4GHz and not 900MHz? If not could I shorten or lengthen the wire in the middle of the corner reflector to a different length so it works for 900 MHz better?

As an aside, do routers that transmit on both 2.4 GHz and 5 GHz use the same antennas for both? Is it because the frequencies are close to 2x of each other?

Answer 1

The wavelength, and hence the antenna design for 2.4 GHz is ~12.5 cm, but the wavelength for 900 MHz is ~33 cm. There would be a number of issues, including poor impedance match and decreased radiation efficiency, with an unknown radiation pattern.

It would be easier to build your own antenna, just requiring some copper wire, and perhaps some insulators and reflectors (e.g. screening) depending on design.

• A Yagi antenna is a flat design, with little wind resistance.
• A "cantenna" uses a food container to make a directional antenna.
• An old satellite dish antenna can be rebuilt for 900 MHz.
• If you want a really high-gain, directional antenna, read J. M. Polard's Amateur Radio Astronomy.