A system for minimizing the effect of null zones in an interrogation zone of a marker detection system. The system includes a reference antenna system configured to produce a first reference electromagnetic field during a first time period. The antenna system also includes a phase canceling antenna system configured to produce a second electromagnetic field substantially in phase with the reference electromagnetic field during the first time period and a third electromagnetic field substantially out of phase with the reference electromagnetic field during the first time period. The phasing of the first field or the second and third fields may be continuously switched while the phase of the other is held constant. A method of spatially shifting null zones in an interrogation zone of a marker detection system is also provided.