The LOH-4 is a traveling wave antenna used in instrument landing system localizer systems to provide azimuthal guidance to aircraft for accurate alignment with runway centerline during approach and landing of aircraft under instrument flight rules.
The most common configuration is an eight-element system, but a fourteen-element system is available for difficult runway configurations with many obstructions. A conversion unit to change an eight-element into a fourteen-element system is available if site conditions are altered over the years of service.
The primary advantages of the LOH-4 traveling wave antenna over the other localizer antennas are an integral monitoring system, high radiation efficiency, and a very directive pattern with vertical radiation lobes that are heavily suppressed. These combined features are unique to the LOH-4.
Each system consists of antenna elements, supports, cable troughs, obstruction lights, distribution cables, monitor cables, distribution unit, monitor combining unit, two detectors, phaser, variable attenuator, fixed attenuator, phase sampler, and mechanical misalignment monitor.