The Role of Propagation Effects in Airborne RF Communication Systems Design

Abstract

Recent years have seen the emergence of Unmanned propagation including ducting and sea clutter [3]- [8]. With Aerial Systems performing roles that use various Radio the recent advent of UAS, large and small, high altitude and Frequency (RF) systems. Thus, there is a need to use accurate low altitude, Air Force designers must now consider signal and broadly capable signal propagation models to capture propagation in many of their RF system designs. While there multi-path effects as well as atmospheric effects in system are a number of papers proposing and outlining the use of requirements analysis. One such model, the Variable Terrain UAS as communication relay links [9]- [13], there are few Electromagnetic Parabolic Equation (VTRPE) model, enables papers analyzing the propagation effects of terrain the required analysis for a wide range of applications. The work environments on the UAS communication link [14], [15].presented in this paper uses VTRPE to analyze signal propagation in multi-path environments and places the results There are a number of empirically derived multi-path and in a system design context drawing conclusions to aid in atmospheric fading models that can be used to analyze the airborne RF systems design.terrain environment [16]- [19]; however, most of these models are best suited to specific conditions and require significant I. INTRODUCTION effort and expertise from the user. Airborne Radio Frequency (RF) systems are generallyThis paper demonstrates the importance of including comprised of some combination of antenna, receiver, signal propagation effects for airborne RF functions. The transmitter, and processing subsystems, and have numerous particular case considered here is communication link, but the military applications. These include radar, communication analysis can be extended to other functions such as radar. It radio relay, and signal collection among many others. The considers sea and land environments as well as ducting and design of a given airborne RF system depends on system standard atmospheres. For the land environment, both functions and the operational environment.ground-to-air and air-to-ground communication links areThe emergence of Unmanned Aerial Systems (UAS) has considered. Calculated figures of merit include received naturally led to proposals for fitting them with RF payloads. power and signal to noise ratio. The latter is discussed in terms of bit error probability and communication link margin.Most of the parameters in the presented communication link subset of RF applications proposed for UAS. Unlike air-to-air returs is scenarios are given assumed values with the exception of the functions, where the number of multi-path signal returns propagation factor which is modeled by the Navy developed small, the air-to-ground and ground-to-air functions are VTRPE (Variable Terrain Electromagnetic Parabolic susceptible to multi-path return. Multi-path signals arrive at Equation) code. VTRPE provides a simple user interface and the airborne receiver delayed in time with re...