  Generally, in the application of subspace migration for detecting locations
of small inhomogeneities, one begins reconstruction procedure with a priori
information of applied frequency. However, mathematical theory of subspace
migration has not been developed satisfactorily when applied frequency is
unknown. In this paper, we identify mathematical structure of subspace
migration imaging function for finding locations of small inhomogeneities in
two-dimensional homogeneous space by establishing a relationship with Bessel
functions of integer order zero and one of the first kind. This expression
indicates the reason behind the appearance of inaccurate locations. Numerical
simulations are performed to support our analysis.
