What is the resolution of airport ground radars?
For surface movement radars (SMR) operating in the 9 - 9,5 GHz band, the pulse length is typically in the order of 40ns. This is equivalent to 12 meters. That would bring the theoretical minimum range to 6 if we ignore transmitter / receiver switching overhead time. 

In practice there is no need for such a short range. Instead a pulse train is transmitted before the antenna is switched from the transmitter to the receiver. This allows the radar to increase the accuracy by averaging multiple reflections, at the price of an increase in minimum range. Typical minimal range will be in the order of 100 meters.

Other SMR systems use continuous wave radar and have a transmitter and receiver antenna in the radar head. These systems don't require to switch between transmitting and receiving and don't have a minimum range. 

The range resolution is in the order of 3 meters, equivalent to the pulse rise time of about 10ns.

The azimuth resolution of a typical SMR is in the order of 0.25 degrees, which is equivalent to 10 meters at 2 km distance. 



Apart from primary radar there are other classes of surveillance systems in use for airport surface detection. 


Secondary surveillance radar (SSR) lacks the accuracy of the SMR and
can only see transponders. But combined with the primary radar allows
for identification of aircraft on the airport surface (i.e. putting
identification labels on the aircraft's primary radar reflection).
Multilateration (MLAT) systems also rely on transponders but are more
accurate than SSR for surface monitoring. These systems require a large number of receivers and are susceptible for radio reflections from buildings.
ADS-B relies on the aircraft (or airport vehicle) transmitting its
position, speed and heading.