To escape from a bear, you don't necessarily have to run first; the main thing is not to be last. This is the basic principle of lightning protection. It is obvious that an antenna will not survive a direct lightning strike, no matter how well it is protected. Therefore, it is important for the antenna to withstand the induced effects of distant lightning strikes. That is, it is best to install the antenna so that the lightning strikes not it or very close to it, but rather a lightning rod located further away.
But what is needed for the antenna to survive a distant lightning strike? Where does the trouble come to the antenna? The trouble comes through the coaxial cable that connects the antenna to the receiver. And, by the way, this trouble also comes to the receiver on the other side of this cable, and it also needs protection.
What is the complexity of protecting antenna inputs and high-frequency circuits in general? Telephone lines are protected - varistor assemblies, large spark gaps are installed, and we usually do not hear stories about a phone burning out due to a thunderstorm. But there is a complexity here.
A telephone line is a low-frequency device; you can install large protective elements that can absorb many joules of energy without interfering with signal transmission. However, a GNSS signal is high-frequency, and every picofarad of capacitance of the protective element counts and weakens the signal. No, antenna inputs can also be protected. There are protective TVS diodes with capacitance in fractions of a picofarad. And there are special assemblies of serially connected regular fast diodes with low capacitance and more powerful protective TVS diodes, and these assemblies have both low capacitance and can absorb the necessary impulse energy.
However, in this armor and projectile competition, one has to be lenient about the fact that the armor is not very thick, and corresponding standards for resistance to high-energy pulses grant some concessions to antenna inputs.
There are antennas with some lightning protection, especially among timing ones. Just understand that this protection is usually relative, guaranteed for 5-6 times, no more. And it is the last line of defense against lightning, not the first. The first and main line of defense is a lightning rod located further away from the antenna and higher than it.
© Eltehs SIA 2023
