What frequencies can a GNSS (Global Navigation Satellite System) antenna pick up?

Question

Am sure that a GNSS antenna can pick up other frequencies than GNSS ones, so is there anyone who tested that theory?

Answer 1

It of course is very important for a GNSS antenna to reject out-of-band radiation (because the signal you want to detect is very weak, you will be utterly deafened if signals from adjacent bands are present at the output of your receive antenna).

So, as a prior:

Am sure that gnss antenna can pick up other frequencies than gnss ones,

that's true for any antenna to a lesser or larger extent; there's no perfectl band-limiting of any system in this universe. But: GNSS antennas will be among the more narrow ones you will meet in the wild.

So, your certainty expressed by "sure" sounds a bit overconfident here!

is there anyone who tested that theory?

Yes, the people building that antenna. Any reasonable antenna you can buy has a datasheet with data that will show its efficiency for a range of frequencies. There's little guesswork involved for electronics systems manufacturers – you just wouldn't build anything involving an antenna that doesn't state over which frequencies it works well.

Now, for GNSS antennas, things are usually a bit more extreme: SNR in GNSS reception is very low – in fact, usually, GNSS is weaker than the thermal noise in your receiver.

To not lose the remaining signal quality to cable losses, it makes sense to have an amplifier close to the actual antenna (see: Friis noise formula). Such antenna-amplifier combinations are often called active antenna.

The thing with amplifiers is that you want them to behave linearly to avoid harmonics and unwanted intermodulation products with other signals; you can only achieve that through very high power consumption and expensive parts, or by filtering to remove all the frequencies you don't want from your amplifier in- and output. So, another front where the assumption that GNSS antennas will be good for much but GNSS bands seems to be built on treacherous grounds.

---

TL;DR: no, to the extent that you mean, commercial GNSS antennas will be pretty restricted to GNSS bands.

Answer 2

Your question seems to display a fundamental misapprehension of a core aspect of antenna theory: resonance.

Antennas operate most efficiently at their designed frequency of resonance, which is largely (but not only) a function of their physical size. As a signal's frequency deviates (higher OR lower) from the antenna's design frequency, the efficiency of the signal capture (for lack of a better term) decreases.

For any particular antenna, you can define it's effective bandwidth by 1) first defining minimum acceptable efficiency in transferring power from the antenna to the feed-line or radio and then 2) understanding how the antenna's performance aligns with that requirement.

I think you'll find that the answer at Calculating bandwidth of antenna? may get you pointed on the right track, and give you some additional terms to read up on.

The short answer to your original question is technically yes but effectively no. Other frequencies outside of the design of your GNSS antenna will impart non-zero energy, but most everything will be on the same order (or LESS) as the same excitation of the local noise floor; meaning that any signal possibly delivered from, say a broadcast FM radio station or a 30GHz source will be substantially less than that of background static and undetectable as a result.