A flight experiment and calculations were conducted to examine the effects of an obstacle on a prototype monopulse SSR. The obstacle was located at a distance around the SSR antenna, and has dimensions of 40m width and 10m height. The experimental results and the calculations both show that the azimuth accuracy of the monopulse SSR is degraded by the obstacle. The azimuth accuracy is more degraded when the obstacle is located in a diffractive region than when it is located in a reflective region. The standard deviation of the azimuth accuracy with the obstacle in the diffractive region is 1.7 times of that without the obstacle, while that with the obstacle in the reflective region is 1.1 times. And the replies from the target are deviated in azimuth by the obstacle. The azimuth deviation of the replies causes split targets in the monopulse SSR. This report also shows that an antenna with a sharp cutoff radiation pattern is effective to suppress such effects caused by the obstacle.

To maintain the safety of air traffic, radio facilities, such as RCAG, NDB, VOR/DME etc., have to operate at high availability. Therefore, for the sites at which maintenance personnel are not permanently stationed, they always monitor the status of these equipment at the maintenance center by a remote control system, and travel to sites for periodic maintenance and failure correction. But a limited number of remote monitoring parameters of the existing remote control system sometimes hinders a good understanding of the status of site facilities.

To improve the existing system for RCAG, an advanced remote control system using a minicomputer is developed here. This system is composed of two subsystems; one is data acquisition and transmission equipment in the facility site, the other is data processing and display equipment in the maintenance center.

The former equipment was made on an experimental basis. The tests have been conducted to evaluate performance of this equipment and good results have been obtained.