Radiolocation with Multiple Directional Antennas

Abstract

All radiolocation methods are concerned with the same problem: determining the direction of the Poynting vector of a radio wave at the point of observation. In this chapter, we will delve into our chosen method of amplitude-based radiolocation, but let us first draw some useful analogies with optical detectors and optical image formation.

A radiolocation method that relies on the amplitude, or power measurements, must involve at least one directional detector. Sensitivity of the detector has a maximum in a known direction, relative to the instrument, and if a maximum reading is obtained, the instrument’s maximum must be aligned with the direction of the wave. This implies that we must measure the power in a number of directions in the vicinity of the putative maximum.

In the approximation of geometrical optics, where the diffraction phenomena are neglected, formation of an image can be viewed as just such a many-directional measurement of amplitude. For every direction within its field of vision, a telescope, or even a pinhole camera, has a preferentially sensitive spot in its image plane. When a wave arrives from that direction, it causes an infinitely narrow maximum readout at the right place in the image plane. We know that it is a maximum, because the adjacent directions are also measured, and yield zero intensity: what we see (what the film or the CCD array sees) is a bright spot, the image of a distant point source.