Study on the Loaded Line Type Electronic Modulator for ILS Glide Path Equipment

Abstract

Mechanical device has been used for almost 30 years in modulation circuit of ILS. This has resulted in comparatively low reliability and performance. Therefore electronic modulators have been developed to get over the degradation of ILS integrity.

Existing electronic modulators with switched line phase shifters, however, seem to be inadequate for high performance. The electronic modulator with loaded line phase shifter has been developed to overcome several difficulties in the existing electronic modulator.

This paper describes the design approach of the loaded line phase shifter and it's monitor, and some characteristics of the electronic modulator and the monitor circuit for the new type of the electronic modulator.

Quantom noise proper to electronic modulator is supressed above 30kHz, so that the interference of adjacent channels above 600kHz is not appeared at the test results. The sensitivity of trouble detection of the monitor circuit is so high that the deviation currect less than ±2.5μA could be detected. The total MTBF of the electronic modulator is estimated by 3.5 times longer than the existing electronic modulator.