Nine antenna elements
Five antenna elements
0.5
Diameter relative to wavelength D/λ
1
1.5
2.5
3.5
4.5
2
3
4
5
80
70
60
50
40
30
20
10
0
Improvement factor relative to
narrow-aperture DF systems
Four elements
Adcock/Watson-Watt
D/λ
= 0.2
Eight elements
Adcock/Watson-Watt
D/λ
= 1.0
Five elements
Correlative interferometer
D/λ
= 1.6
Nine elements
Correlative interferometer
D/λ
= 4.3
Rohde
&
Schwarz
Maximum permissible diameter of the DF antenna relative to the wavelength for unambiguous DF results
for up to 50
% environmental reflections
16
DF antennas using nine elements and the correlative inter-
ferometer DF method offer by far the widest aperture and
therefore enhanced accuracy and sensitivity (see top fig-
ure). As a result, they have a considerably greater improve-
ment factor (compared with small-base DF antennas) than
antennas containing only five elements, for example.
The considerably higher immunity to reflections offered by
DF antennas with nine elements (compared with five-ele-
ment DF antennas) can be mathematically proven by sim-
ulating the DF antennas in a two-wave field (direct wave
and reflected wave). First, the DF values that a DF antenna
in a two-wave field would produce are calculated one after
the other, the field strength of the direct wave being twice
as high as that of the reflected wave. Since the DF error
depends on the frequency, the angle of incidence and the
phase angle of the reflected wave, all possible combina-
tions of these parameters are simulated. Then the RMS
value is determined from the individual DF errors.
The table below shows that DF antennas with nine ele-
ments provide considerably higher DF accuracy than com-
mercially available five-element DF antennas. It is assumed
that the five-element DF antennas exhibit a system DF ac-
curacy of 1° RMS in a reflection-free environment. Since
the Rohde & Schwarz DF antennas use eight elements for
direction finding in the frequency range above 1.3 GHz, an
eight-element DF antenna is simulated in this frequency
Nine antenna elementsFive antenna elements0.5Diameter relative to wavelength D/λ11.52.53.54.5234580706050403020100Improvement factor relative tonarrow-aperture DF systemsFour elementsAdcock/Watson-WattD/λ= 0.2Eight elementsAdcock/Watson-WattD/λ= 1.0Five elementsCorrelative interferometerD/λ= 1.6Nine elementsCorrelative interferometerD/λ= 4.3Rohde&SchwarzMaximum permissible diameter of the DF antenna relative to the wavelength for unambiguous DF resultsfor up to 50% environmental reflections16DF antennas using nine elements and the correlative inter-ferometer DF method offer by far the widest aperture andtherefore enhanced accuracy and sensitivity (see top fig-ure). As a result, they have a considerably greater improve-ment factor (compared with small-base DF antennas) thanantennas containing only five elements, for example.The considerably higher immunity to reflections offered byDF antennas with nine elements (compared with five-ele-ment DF antennas) can be mathematically proven by sim-ulating the DF antennas in a two-wave field (direct waveand reflected wave). First, the DF values that a DF antennain a two-wave field would produce are calculated one afterthe other, the field strength of the direct wave being twiceas high as that of the reflected wave. Since the DF errordepends on the frequency, the angle of incidence and thephase angle of the reflected wave, all possible combina-tions of these parameters are simulated. Then the RMSvalue is determined from the individual DF errors.The table below shows that DF antennas with nine ele-ments provide considerably higher DF accuracy than com-mercially available five-element DF antennas. It is assumedthat the five-element DF antennas exhibit a system DF ac-curacy of 1° RMS in a reflection-free environment. Sincethe Rohde & Schwarz DF antennas use eight elements fordirection finding in the frequency range above 1.3 GHz, aneight-element DF antenna is simulated in this frequency
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