TABLE OF CONTENTS Picking up on loose ends of radar lore
The radar line of sight
The ionosphere as absorber, refractor, reflector, and polarizer
The troposphere, complex but definable
Deriving the far field of an antenna, and a target
Some radar rules of thumb
Several other brief quantitative notions and a list of rules of thumb should be included in any set of radar fundamentals. Some are good for general day-to-day use; others are important to detailed radar design calculations. They are pulled together in this chapter without concern for their relevance to each other and only because they are valid radar lore.
Solving for the optical horizon at a given range is a simple problem in trigonometry, as shown in Figure 8.1. The range to the horizon is given in Equation (8.1). Radio frequency waves refract (bend) as they propagate through the many layers of the atmosphere [Meeks, 1982]. To account for refraction, we multiply the Earth s radius by a refraction factor, as given in Equation (8.2). Refraction factors that are constant as a function of altitude are often used. Common constant refraction factor values are 4/3 and 6/5. Refraction factors that are exponential with altitude are also used. Often, an approximation to the range to the horizon is used because 2 k r R E h >> h 2. This approximation is acceptable for the vast majority of ground-based and airborne radar geometries. This approximation is unacceptable
