Content

• Introduction.
• The purpose and objectives of the study.
• Overview of the Doppler direction finder with a rotating antenna.
• Conclusion.
• References.

Введение

Directional radio – radio engineering, the subject is to detect the direction of the various objects to determine their location and motion parameters. Direction – finding based on the reception of the reflected from various objects (targets) or their own radio radiation of objects. By the nature of the signal which is received, radar stations, divided into three types: active, with active and passive response [1].

In active radar signal is received, formed after the reflection from the target radiation (probe) signal.

In radar systems with active response to the radar site (RLN) is established the defendant – transceiver device that takes a probing signal, amplifies and re – emits it in the direction of the radar (SAR). This is done to increase the noise immunity or increase the range of the radar.

In passive radar probing signal is not emitted, and accepted only the intrinsic emission of radiation of the radar facility [4].

In this master work would be considered passive radar

The purpose and objectives of the study

The purpose of this master work – a comparative analysis of schemes Doppler direction finder, and the delimitation of their application.

The main objectives of the study:

1. Analysis methods of Doppler direction – finding equipment;
2. description of different variants of schemes Doppler direction finder;
3. Determination of advantages and disadvantages of each of the schemes;
4. Determination of applications under study methods.

Subject of research: Block diagrams of direction finders operating on the basis of the Doppler method for the determination of the coordinates.

Overview of the Doppler direction finder with a rotating antenna.

There is an option of building without a fixed Doppler direction finder antenna.

The principle of operation of the direction finder is as follows.

The receiving antenna is omnidirectional in the horizontal plane of the vibrator that moves in a circle of radius R, with an angular velocity equal to Ω.

When you receive signals in a rotating antenna will be induced electromotive force is modulated in phase with the frequency Ω. The phase modulated envelope fluctuations will be a continuous function of the azimuthal angle θ. After amplification, the signals received in the reception path as a result of detection can be allocated to the envelope. By comparing its phase to phase voltage reference, it is possible to determine the bearing to the source of radio emission [12].

The reference voltage used variations of the local oscillator with frequent Ω, consistent with the rotation of the antenna so that the zero phase of these oscillations will occur during the passage of the antenna through the northern direction of the meridian [10].

To highlight the difference between the phases, using the following method. By mixing the received signal in the second converter with a voltage crystal oscillator, the voltage obtained by the second intermediate frequency with the same law of phase modulation, as adopted by the oscillation. This voltage is delayed in the delay line. After that, the delayed signal and the first intermediate frequency signal is fed to the third inverter, which are distinguished from the fluctuations of the phase change the law, the law changes the phase difference of the envelope of the direct and delayed signals. The detector is allocated the value of the third intermediate frequency, the phase which corresponds to the azimuth direction finding station [12].

Voltage from the phase detector and the reference oscillator are fed to the light phase, from which the bearing is read.

Consider the principle of the Doppler direction finder with a rotating and a stationary antenna.

The motor rotates the movable antenna in a circle of radius R, and an angular velocity equal to Ω, on the same shaft with the motor to be the same reference voltage generator that generates vibrations, the phase shift is equal to zero at the passage of a rotating antenna northbound [10]. This tension feeds the indicator. Supporting non-directional antenna is used to convert the signal frequency to a stable frequency determined oscillator stabilized quartz. Stress from both antennas are fed to separate amplifiers and mixers, powered by the generator in common. The resulting intermediate frequency voltage separately amplified in the intermediate frequency amplifiers. The intermediate frequency channel of the auxiliary antenna is mixed in the second mixer with a quartz oscillator frequency voltage fkv. The conversion rate is obtained by f_if — f_qo. The voltage at this frequency is mixed in the second mixer IF amplifier with an output voltage of the main channel, forming a voltage of frequency f_if — (f_if — f_qo) = f_qo. Thus, the voltage at the output of the second mixer has a stable frequency that is equal to the frequency of the quartz oscillator and is independent of signal frequency and the frequency of the first local oscillator, and also on their possible changes. After further amplification the signal voltage amplitude is subjected to restriction and fed to the phase detector, both directly and through the filter time delay[11]. Where the signal is delayed by time τ, equivalent to a shift of the antenna at an angle β = Ωτ. This is achieved by reducing the index of phase modulation in the Doppler direction finder with a large base [10]. The phase detector selects the voltage switching frequency. The latter is compared in phase with the reference voltages in the indicator. Count on the indicator gives a direct bearing value.

Conclusion

The considered variants of the Doppler direction finder can solve the problem of reducing the errors of direction finding, arising out of - for the variability of the field phase of the transmitter due to modulation of both the nature and instability of the transmitter. The advantage of these finders is the possibility of direction &ndash finding stations operating with any type of modulation.

In the master work will be considered the advantages and disadvantages of each of the schemes and identify capabilities and limits of both.

In writing this abstract master work is not yet completed. Final completion: January 2013. The full text of the and materials on the topic can be obtained from the author or his head, Sorochan Anatoly, after that date.

References

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