dc resistance of 50 ohm antenna

Hi, all:

As we know RF components (for example RF load/terminator) has high frequency impedance of 50Ohm (telecommunication), most of them also have DC resistance of 50 Ohm. Why and how do they get 50Ω DC resistance?

How about antennas? Do all of them have 50Ω DC resistance? For example antenna of GSM radio base station.

Thanks.

Except for ver y special cases (e.g. a terminated travelling wave antenna), no antenna has 50 ohm DC resistance, zero or infinite can be expected.

Terminators or attenuators simple use real frequency independant resistors.

How about antenna of GSM/CDMA radio base station? Zero or open? Which one is more common?

Added after 24 minutes:

I checked some technical notes about antenna of GSM macro radio base station, many of them are DC grounded for lighting protection.
Is there any commercial DC open antenna for GSM macro radio base station?