DSB Doppler VOR has the advantage in reducing the siting effects and bearing errors as compared to conventional VOR and SSB Doppler VOR, and adoption of DSB Doppler VOR is being considered in Japan.

The performance test have been carried out on the course characteristics and the stability of the system utilizing the Antenna Test Tower in the Electronic Navigation Research Institute and at Choshi, east of Tokyo.

This paper describes an analytical study on some operational problems in DSB Doppler VOR and its performance test results.

The microwave landing system (MLS) is under development as a replacement for ILS. The time reference scanning beam system (TRSB) was selected as the preferred system for worldwide standardization by ICAO recently.

The most serious threat to an accurate angle measurement is multipath where signals arrive at the aircraft almost simultaneously from both direct and reflected propagation paths. The direct and reflected signals can illuminate the aircraft at slightly different times (out-of-beam multipath) or at the same time (in-beam multipath).

This paper presents the optimum gate width of time gate tracker which rejects out-of-beam multipath, and the error characteristics of in-beam multipath and its reduction.

The optimum gate width is analyzed considering sidelobe level of the scanning antenna, threshold level of receiver and tracking function of the gate. The optimum gate width is 2BW, where BW is beam width of the scanning antenna, and the required accuracy of the gate position is ±0.2BW. Also, it is necessary that sidelobe level of the scanning antenna is less than -15dB. Under these conditions, the gate rejects the out-of-beam multipath that is lower level than the direct signal by at least 1dB.

Effectiveness of reduction of in-beam multipath errors by motion averaging and staggering of the transmitter repetition period are examined with computer simulation and the experiments using the azimuth subsystem. Experimental values agree well with the simulation results, and reduction rate of 1/2∼1/3 is obtained

The performance of the ILS glide path is affected with the effects of multipath scattering and ground.

The M-array glide path system is used in place of the Null reference system in order to reduce the effects.

This paper describes a reduction factor of the multipath scattering effects of the M-array system compared with the Null reference system.

The ground effect is discussed on the M-array and Null Reference system by means of calculation of reflected waves. The result shows the ground near the glide path antenna has a greater effect to the M-array system than to the Null reference system on the performance. The ground far from the antenna has a relatively large effect to the Null reference system than the M-array system.