Analysis of DME Signal Strength in Approach Direction under Two-Ray Model

Starting from the theory of phase superposition of radio wave specular reflection, the causes of DME signal intensity depression in the mid-long distance, which is common in flight inspection of GP DME, are deeply analyzed and studied. The variable conditional path gain Equation is derived by using the double line model and Snell's Law. By establishing the mathematical simulation model of Matlab and comparing with the actual flight inspection results, Finally, it is found that the phase superposition of the direct signal of the gliding DME antenna and the ground reflected signal at a specific position in the air is the main reason for the depression of the GP DME signal strength at the mid-long distance, and an effective solution to eliminating the signal strength out of tolerance at a specific position is proposed.