In a DLL circuit between a phase comparator and a digital filter there is provided a signal switching portion preventing control signals UP and DOWN from being transmitted after a clock enable signal extCKE is activated and before a predetermined period of time elapses. Portions of the radar signal that are reflected by entities located beyond the second side of the wall are detected. Read and write pointers are provided to designate which of said frame buffers that are used to be readwrite accessed at each point in time. Hereby an antenna means, which can be made compact, and can operate in more than one frequency band is obtained.