The interference suppression antenna for the near‐field monitor of category III ILS

It is well known that the ILS Localizer (LLZ) course may be deviated by aircraft passing above the LLZ antenna. The course deviation is observed not only by other aircraft approaching to a runway but also by the ILS monitor. This phenomenon may cause an alarm in the ILS monitor and halt category III LLZ operation, because the tolerance for unexplained course deviation and its duration is tighter in category III LLZ than in other categories. In this paper, a new antenna (the interference suppression antenna) for the near field monitor (NFM) is proposed that can suppress unnecessary alarms generated by this phenomenon. First, the LLZ course deviation and its duration as observed by the NFM due to passing aircraft above the LLZ are analyzed. Next, the course deviation is calculated when the interference suppression antenna, which consists of an end-fire array antenna and a broadside array, is used. The relationship between the aircraft location, the course deviation, and its duration period as received by the NFM is determined. When this new antenna is used, the course deviation at the NFM and its duration can be reduced substantially from those obtained by the conventional antenna. © 1997 Scripta Technica, Inc. Electron Comm Jpn Pt 1, 80(7): 51–60, 1997