Introduction into Theory of Direction Finding

Introduction
Applications of direction finding
While direction finding for navigation purposes (referred to as cooperative direction finding) is becoming less important due to the availability of satellite navigation systems, there is a growing requirement for determining the location of emitters as the mobility of communications equipment increases:
. In radiomonitoring in line with ITU guidelines
Searching for sources of interference ;
; Localization of non-authorized transmitters
. In security services
Reconnaissance of radiocommunications of criminal ;
organizations
. In military intelligence [1]
; Detecting activities of potential enemies
Gaining information on enemy‘s communications order ;
of battle
. In intelligent communications systems
Space division multiple access (SDMA) requiring ;
knowledge of the direction of incident waves [2]
. In research
; Radioastronomy
; Earth remote sensing
Another reason for the importance of direction finding lies
in the fact that spread-spectrum techniques are increasingly
used for wireless communications. This means that
the spectral components can only be allocated to a specific
emitter if the direction is known. Direction finding is
therefore an indispensable first step in radiodetection, particularly
since reading the contents of such emissions is
usually impossible.
The localization of emitters is often done in a multistage
process. Direction finders distributed across a country
allow an emitter to be located to within a few kilometers
(typ. 1% to 3% of the DF distances) by means of triangulation.
The emitter location can more precisely be determined
with the aid of direction finders installed in vehicles.
Portable direction finders moreover allow searching within
the last 100 m, for instance in buildings…….( Read Full Article in .pdf )

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