Cell Towers Can Double as Cheap Radar Systems for Ports and Harbors (2014)

No? It's significantly smarter and easier to use AIS.

AIS, like ADSB, is secondary surveillance - not radar. It's a mechanism for cooperative targets with functioning electronics to identify themselves and provide operational information. However, it does not detect uncooperative entities or those not equipped with the electric transponders. For example, AIS won't show you an enemy's invading fleet, and ADSB won't show incoming missiles. Those needs are fulfilled by primary surveillance radar, like the passive solution from this article.

If you're honestly worried about being bombed then you need to buy radar.

With your logic all I have to do is take the additional step of disabling your cellular infrastructure before I steam up to your port.

This is not a tactical solution. It can only be for convenience or cost savings. In that realm, AIS is the obvious answer.