Abstract of master's work "Doppler single-channel direction finder research for civil aviation"
Содержание
- Introduction
- 1. Theme urgency
- 2. Goal and tasks of the research
- 3. A brief overview of commonly used methods of direction-finding purposes
- 4. Description of the principles of Doppler and pseudo-Doppler direction finders
- Conclusion
- References
Introduction
Direction finding is the definition of the direction to an object, its angular coordinates. It can be optical, electronic, acoustic etc. Using radio direction-finding, ie determining the direction of the source of emission, is called direction finding. [1]
1. Theme urgency
The current stage
of development of aviation is characterized by quantitative and
qualitative
change of aircraft, increasing the intensity and speed of flight, which
requires increasing the efficiency of radio systems to ensure flight.
The development of
complex radio systems requires comparing different implementation for
the
optimal ones. [2]
While the bearing
of navigational purposes become less important because of the presence
of
satellite navigation systems, there is an increasing need to locate
sources of
emission as there is a rapid increase in the number and variety of
communications equipment in such areas as:
• 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
2. Goal and tasks of the research
Purpose of the work is to study single-channel Doppler direction finder. It's necessary to analyze existing methods of direction finding, discover the essence of the chosen method, to define the basic parameters and characteristics of the direction finder based on this method and bring its advantages and disadvantages. In conclusion it must be made a comprehensive analysis of the data and to evaluate the effectiveness of the method.
3. A brief overview of commonly used methods of direction-finding purposes
Amplitude DF
methods are based on the directional properties of antennas.
Finders based on the phase direction finding method, get the necessary information from the spatial arrangement of lines or surfaces of equal phases.
4. Description of the principles of Doppler and pseudo-Doppler direction finders
In recent years, widely baseline phase finders are successfully applied using the Doppler effect caused by the phase modulation occurring in a circular rotation of the receiving antenna .Essentity of Doppler
effect is that the relative (mutual) displacement transmitter and
receiver
alters the phase (and hence the frequency) of the received
oscillations. The
frequency of the received oscillations becomes different from the
frequency of
the emitted.
of
the
circumferential radius R in the field produced by a remote transmitter
frequency
electromagnetic waves.
Figure
7. The
nature of the phase increment in the direction finder using the Doppler
effect
Conditional antenna
rotation phase increment therein EMF induced in the negative period of
time
when the antenna is removed from the transmitter. In this case, the
projection
of the velocity of the antenna to the line OO' coincides with the
direction of
propagation of radio waves (Fig. 7). Positive phase increment when the
antenna
is close to the transmitter, and equals zero when the antenna moves
perpendicularly to the direction of propagation.
Phase emf induced
in the antenna is located in the center of the circle (point D) is
taken as
equal to the starting and is 
By rotating the
antenna the instantaneous phase induced electromotive force differs
from 
value on
ie,
the voltage in the antenna phase modulated frequency 
, and phase modulating
oscillation corresponds to the azimuth direction finding station.
To
identify the phase of these oscillations and consequently determine the
azimuth
of the transmitter are fed to the phase meter that compares the phase
of the
reference voltage.
In practice,
instead of applying the rotating antennas arranged circumferentially
fixed
antennas which by means of mechanical or electronic switches are
connected
alternately with a frequency appropriate to the receiver
input.
Figure 8 - Block
diagram of a single-channel Doppler finder
The use of the
Doppler effect and possibly with ILS systems which use a rotating
antenna or a
number of fixed antenna switched phase of the emitted signal is
modulated, and
the modulation parameters carry information about the bearing of the
opposite
object retrievable when the signal received by the receivers in the
facility.
In practice the
spacing between the individual elements of the antenna system is
typically
chosen equal to 1/3 of the minimum wavelength. If this condition is
met, the
antenna direction finder on the Doppler effect can meet the
requirements of
wide-aperture antenna systems at low cost:
• Provide high
security multi-path due to the spatial selection;
• To provide high
sensitivity.
The disadvantage is
the need of Doppler expenditures a certain period of time, because for
determining
bearing all elements of the antenna system should be scanned at least
once. So at
speed 170 Hz VHF / UHF bands one scan takes about 6 ms. But this
disadvantage
is not so significant when you consider the benefits of the method.
advantages:
- The presence of
only one channel
- Ease of
implementation (using a simple antenna and circuit-based)
- High accuracy
Conclusion
This master thesis is devoted
to the actual scientific and technical problem-finding study of systems
that
are applicable to civil aviation in niches days in which the main
requirements
are high accuracy and speed of measurement.
Remark. In
writing this essay master's work is not yet
complete. Final completion: December 2013. Full text of the work and
materials
on the topic can be obtained from the author or his supervisor after
that date.
References
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