B757 captain reported autopilot intercepted false localizer on approach.

Attributes
ACN	1602111
Time
Date	201812
Local Time Of Day	0001-0600
Place
Locale Reference	TUL.Airport
State Reference	OK
Environment
Flight Conditions	VMC
Aircraft 1
Make Model Name	B757-200
Operating Under FAR Part	Part 121
Flight Phase	Initial Approach
Flight Plan	IFR
Component
Aircraft Component	Approach Coupler
Person 1
Function	Captain Pilot Flying
Qualification	Flight Crew Air Transport Pilot (ATP) Flight Crew Instrument Flight Crew Multiengine
Events
Anomaly	Aircraft Equipment Problem Less Severe Deviation - Altitude Excursion From Assigned Altitude Deviation - Procedural Clearance Deviation - Track / Heading All Types

Narrative:

Descending to tul. Heading to the marker for the approach to [runway] 18L; approximately 2 miles before the localizer; the aircraft intercepted something like a false localizer and started turning to a heading parallel to the actual final course. We were caught by surprise. I kicked off the autopilot and turned back towards the marker as we were on the visual. But after all the turns; it took a bit to figure out again where we were. We may have gotten lower than normal during this time; but we reestablished a normal approach to landing.my question is; what happened? Why did the aircraft turn. I've seen it before; but not often enough to expect it.

Original NASA ASRS Text

Title: B757 Captain reported autopilot intercepted false localizer on approach.

Narrative: Descending to TUL. Heading to the marker for the approach to [Runway] 18L; approximately 2 miles before the localizer; the aircraft intercepted something like a false localizer and started turning to a heading parallel to the actual final course. We were caught by surprise. I kicked off the autopilot and turned back towards the marker as we were on the visual. But after all the turns; it took a bit to figure out again where we were. We may have gotten lower than normal during this time; but we reestablished a normal approach to landing.My question is; WHAT happened? Why did the aircraft turn. I've seen it before; but not often enough to expect it.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.