If I were trying to detect cellphones by detecting their rf communication with cell towers I would need an antenna and an rf detector which connects to the antenna. Cell phones operate at a variety of frequencies, from 700MHz to upwards of 2600MHz (at least as I have seen from my limited research).
I am not very well versed in rf, but it seems that in order to be able to reasonably detect cell phones I would need an rf antenna that has a somewhat broad range. Maybe 800MHz to 1500MHz. Is this a reasonable antenna? Most of the small rf antennas for embedded devices seem to be specd for a single frequency, and have somewhat low gain for frequencies lower or higher than the set one.
Is it possible to even detect this range with a single antenna?
Sorry for my lack of rf experience.