B737-800 First Officer reports TCAS RA during descent on the FLCON 3 arrival with evasive action taken. The target is co-located with the reporter's aircraft laterally and vertically. After further alerts the TCAS is selected to TA only.

Narrative

In the descent phase on the FLCON 3 RNAV arrival; level at 22;000 Feet; TCAS gave a TA but with no target on the navigation display (ND). A few seconds later this turned into an RA commanding a descent of approximately 1500 FPM. The Captain was flying and immediately initiated a descent and commanded me to advise ATC; which I did. ATC told us there was no known threat and cleared us to descend to 14;000 feet. In the descent we observed a TCAS RA target on the ND. It was indicating exactly on top of us; no separation; 0 feet altitude difference; and stationary (staying with us). We discussed this briefly and concluded that the RA was obviously a false alarm. We leveled at 14;000 feet and continued inbound; then received a descent to 12;000 feet and turn direct to DOEVR. We then received another TA followed immediately by an RA and began a second descent at 1400 FPM as commanded. I notified ATC at approximately 11;700 feet MSL and was told that there was no threat observed in our vicinity; but that traffic was climbing up below us and we should not descend below 11;000 feet. We observed again that the TCAS target was exactly on top of us with no separation and co-altitude. The commanded descent was a constant 1400 FPM. We leveled at 11;000 feet and ignored the RA. At DOEVR we turned westbound and I turned the TCAS to 'TA only.' We continued to receive more false alerts for the remainder of the descent. Following this event the Captain phoned the number provided by ATC and was informed that there was no loss of separation between aircraft.