JPH02248880A - Radio wave incoming direction detector - Google Patents

Abstract

PURPOSE:To detect a radio wave incoming direction by extracting a Doppler frequency signal component of a radio wave with an antenna mounted at a point other than the center of rotation on a turntable to remove a carrier component after a limiting of amplitude and a DC conversion. CONSTITUTION:A turntable 2 having a non-directive antenna 1 mounted at a circumferential part is rotated to receive an AM modulation radio wave. A received signal from the antenna 1 is passed through a BPF 3. The Doppler frequency varies with the rotation of the antenna 1 and an amplitude is limited constantly with a limiter 4. A frequency variation component, namely, a Doppler frequency variation component as output of the limiter 4 is converted with an FM demodulator into a DC signal and a carrier component is removed from the DC signal with an LPF 6, an output of which is recorded with a recorder 7 synchronizing the rotation of the turntable 2. From the results of the recording, an incoming direction of the AM modulation radio wave can be determined.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an apparatus for detecting the direction of arrival of radio waves, and particularly to an apparatus for detecting the direction of arrival of AM and FM modulated radio waves using an omnidirectional antenna.

[Summary of the invention] An antenna is rotated in a circular orbit, a Doppler frequency signal component is extracted from radio waves received by the antenna, and a DC signal is obtained in which the carrier component is removed in response to the frequency fluctuation component of the signal component. This device detects the direction of arrival of radio waves from this DC signal.

[Prior Art] Conventionally, in order to detect the direction of arrival of radio waves, a directional antenna has been used, and the direction of arrival has been detected from the intensity of the radio waves received by this antenna.

[Problems to be Solved by the Invention] However, in order to accurately determine the arrival direction of radio waves using the conventional method described above, a special antenna with sharp directivity is required. In this way, with conventional methods, the strength of the received signal and the receiving sensitivity of the antenna must be taken into account, and it is difficult to prepare a directional antenna that is suitable for the radio waves to be detected, and is therefore impractical. was.

[Object of the Invention] Accordingly, an object of the present invention is to provide a device that can easily and accurately detect the direction of arrival of AM and FM modulated radio waves using an omnidirectional antenna by utilizing the Doppler effect.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a first antenna mounted on a turntable other than the center of rotation, and a Doppler frequency signal component of radio waves received by the first antenna. a first Doppler frequency signal component extracting means for extracting a Doppler frequency signal component; a first amplitude limiting means for limiting the amplitude of the extracted Doppler frequency signal component; and a first amplitude limiting means for converting the frequency fluctuation component of the amplitude limited Doppler frequency signal component into a direct current. The gist of the present invention is to include a first converting means for converting the DC signal, and a first carrier component removing means for removing a carrier component from the signal converted to DC.

In addition to the above-mentioned means, the present invention also provides a second antenna installed at the rotation center position of the turntable;
FM modulation component extracting means for extracting an FM modulation component of radio waves received by the antenna; second amplitude limiting means for limiting the amplitude of the extracted FM modulation component; a second converting means for converting, a second carrier component removing means for removing a carrier component from the DC signal converted by the second converting means, and both outputs of the first and second carrier component removing means; and a comparison means for comparing.

[Operation] In the present invention, when the turntable is rotated, a Doppler effect occurs in the direction of arrival of radio waves, and a frequency shift occurs by the Doppler frequency ±fD. Therefore, the output DC signal of the first carrier component removing means or the comparing means fluctuates in the positive and negative directions according to the frequency shift, fo=o.
The rotational position becomes the direction in which the radio waves arrive.

[Examples] The present invention will be described below with reference to examples shown in the drawings.
FIG. 1 shows an embodiment of a device for detecting the arrival direction of AM modulated radio waves according to the present invention.

In the figure, 1 is an omnidirectional antenna, 2 is a turntable, 3 is a band pass filter (BPF), 4 is a limiter, 5 is an FM demodulator, and 6 is a low pass filter (LPF).
), 7 is a recorder, and 8 is a motor. The omnidirectional antenna 1 is attached to a portion other than the center of the turntable 2, which is rotated counterclockwise by a motor 8, for example, to a circumferential portion thereof.

Further, the recorder 9 records the output of the filter 6 in synchronization with the rotation of the turntable 2.

Next, the operation of the embodiment shown in FIG. 1 will be explained with reference to FIGS. 2 and 3.

AM modulated radio waves are received by rotating a turntable 2 having an omnidirectional antenna l attached to its circumference. Here, when the turntable 2 is rotated as shown in Fig. 2, the Doppler effect occurs as the antenna 1 approaches or moves away from the arrival of radio waves, and the Doppler frequency ±f
A frequency shift occurs by D. When radio waves arrive from the left as shown in Figure 2, if the antenna position is changed from ■ to ■, the deviation of fD becomes as shown in Figure 3, and the fundamental frequency f0
On the other hand, it fluctuates by ±fD in a period of 2π. The arrival direction of the radio wave is detected from this Doppler frequency shift.

The direction of arrival of the radio waves is within one rotation of the turntable 2.
Antenna 1 approaches the direction of arrival (+fo).

It exists until it moves away (fo). In other words, the location where the Doppler frequency becomes 0 during this period is the arrival direction of the radio wave, and is a position delayed by 90 degrees from the location where +fD is maximum. In Figures 2 and 3.

When the antenna position is rotated from ■→■→■, fD
It can be seen that the position of ■ where =O is the arrival direction of the radio wave.

As a method for detecting this position, for example, as shown in FIG.
3, the Doppler frequency fluctuates as the antenna 1 rotates, and the limiter 4 limits the amplitude to a constant level, and the FM demodulator 5 converts the frequency fluctuation component, which is the output of the limiter 4, that is, the Doppler frequency fluctuation. The component is converted into a DC signal, and the carrier component is removed from this DC signal by LPF6. The output of the LPF 6 is recorded by a recorder 7 in synchronization with the rotation of the turntable 2. Recorder 7
Referring to the record of , as is clear from Figure 3, the positions where fD = o while the Doppler frequency fD changes from 0 to - are ■, ■, ■, and therefore, AM modulated radio waves arrive from these positions. You can easily know the direction.

Although FIG. 2 shows the rotation in the counterclockwise direction, the same applies to the case of clockwise rotation.

In the method of the above-described embodiment, the direction of arrival of radio waves is detected using the shift of the Doppler frequency.
The measurement antenna may be non-directional, and measurements can be made satisfactorily even with an antenna that does not have particularly high sensitivity.

However, the larger the Doppler frequency shift, the easier it is to detect. The Doppler frequency fD is.

■ It is given by fD = -coSφ λ and is proportional to the speed, so it is desirable that the rotation speed of turntable 2 be faster.Also, as shown in Figure 2, even at the same rotation speed, the movement deviation of antenna 1 It is better to have a larger diameter of the turntable so that The figure shows another embodiment of the present invention for detecting the arrival direction of FM radio waves.

In the same figure, the same reference numerals as in FIG. Fix it in the center. The antenna 1' is sequentially equipped with a second band pass filter 3' (BPF), a limiter 4', an FM demodulator 5', and a low pass filter 6'.
(LPF) are connected to each other, the output of the LPF 6.6' is given to a comparator 8, and the comparison output is recorded by a recorder 9 in synchronization with the rotation of the turntable 2.

Next, the operation of the above embodiment will be explained with reference to FIGS. 5, 6, and 7.

In FIG. 4, the antenna 1' is fixed, and the antenna 1 rotates on its circumference together with the turntable 2 to receive FM radio waves.

Receive signals from antennas 1 and 1', respectively, with BPF 3.3'
The desired frequency component is taken out by the limiters 4, 4', and the amplitude is limited to a constant value, and then the FM demodulator 5,
5' converts the frequency fluctuation components output from each limiter into a DC signal, and LPF 6.6' removes the carrier component from each DC signal. LPF6.6
The outputs of ' are compared by the comparator 8, and the fluctuation of the difference between the respective outputs is recorded by the recorder 1 in synchronization with the rotation of the turntable 2.

First, consider a state in which both antennas 1 and 1' are stationary. Here, since there is a distance difference between antennas 1 and 11, a time difference of Δt occurs during reception. But F.M.
When the modulation frequency is fa, the time Δt of one cycle is Δt
” 1 / f a and Δta) Δt, then
The time difference between antennas 1 and 1' is negligible. Therefore, when antennas 1 and 1' are both stationary, the waveforms received by both antennas are the same regardless of the antenna position on the circumference of turntable 2, and the difference output from comparator 9 is 0. be.

Next, when the turntable 2 rotates (when the antenna 1 rotates), the Doppler effect occurs as the antenna 1 approaches or moves away from the arrival direction of the radio waves, producing a Doppler frequency fD. Therefore, the frequency fluctuation component of antenna 1 is, with respect to that of antenna 1',
The Doppler frequency fD is increased or decreased.

In Fig. 5, when the antenna 1 moves from ■ to ■,
fD gradually increases and reaches its maximum at the position of ■. ■From■
As you move to , fD gradually decreases, and at the position of ■
D=o. When moving from ■ to ■, fD increases to the negative side and reaches the maximum at ■. Further, when moving from ■ to ■, fD approaches O, and fo becomes o again at ■.

If this is expressed as a waveform, it will look like Figure 6 (actually,
Relative to the FM modulation frequency, the Doppler frequency is low enough that the variation of antenna 1 relative to antenna 1 is more gradual).

If the waveform signal obtained in FIG. 6 is converted into a DC signal, compared by the comparator 9, and the difference is taken, this is the fluctuation component of the Doppler frequency.

As can be seen from Figures 5 and 6, the direction of arrival of the radio wave is at the position (■) where fo increases to the + side and then decreases to zero. If the fluctuation component of this Doppler frequency is recorded on the recorder 9 in synchronization with the rotation of the turntable, the result will be as shown in Fig. 7, (2).

Since fD=0 in (1) and (2), the direction of arrival of the radio waves can be known from this.

In the embodiment described above, the direction of arrival of radio waves is detected by using the deviation of the Doppler frequency, so the measurement antennas 1 and 1' may be omnidirectional and do not have particularly high sensitivity. Measurement is also possible with an antenna.

However, if the FM modulation shift of the received wave is too large, it becomes difficult to detect the Doppler frequency.

It is desirable to have a large Doppler frequency shift to facilitate detection.

The Doppler frequency fD is.

■ It is given by f O = -cosφ λ and is proportional to the speed, so it is desirable that the rotation speed of the turntable 2 be faster.Also, even at the same rotation speed, the turn table 2 should be rotated so that the movement deviation of the antenna 1 becomes large. It is better if the diameter of table 2 is also larger.

In the embodiments shown in FIGS. 1 and 4, the turntable 2 is placed on a horizontal surface and only the table surface on which the antenna 1 and/or 1' is installed is rotated to receive radio waves.
The direction of arrival of radio waves coming in from the horizontal direction is detected.

In contrast, as shown in FIGS. 8 and 9.

By making it possible to change the angle of the turntable itself, it becomes possible to detect the direction of arrival (elevation angle) of reflected waves, etc. coming from diagonal directions in addition to the horizontal direction.

Further, the recorder is just an example, and any recorder may be used as long as it can determine that fD = 0.

[Effects of the Invention] As explained above, according to the present invention, since the arrival direction of radio waves is detected by frequency shift using the Doppler effect, the above detection can be easily and accurately performed even when an omnidirectional antenna is used. becomes. Moreover, there is no need to take into account the strength of the received signal or the reception sensitivity of the antenna; all you need to do is simply receive the signal, so it can be used even if the antenna's omnidirectional characteristics are poor to some extent. It is true.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing the relationship between the direction of arrival of radio waves and the antenna in the embodiment of FIG. 1, and FIG. 3 shows the deviation of the Doppler frequency fD. FIG. 4 is a diagram showing another embodiment of the present invention, and FIG. 5 is a diagram showing the relationship between the arrival direction of radio waves and the antenna in the embodiment of FIG. 4. FIG. 6 is a diagram showing frequency fluctuations of received radio waves at antennas 1 and 1', FIG. 7 is a diagram showing changes in Doppler frequency (output waveform of comparator 9), and FIGS.
FIG. 5 is a diagram showing a modification of the embodiment shown in FIGS. 1.1'・・・・・・Omnidirectional antenna, 2...
・・・・・・Turntable, 3.3' ・・・・・・
...BPF, 4,4'...Limiter, 5,5'...FM demodulator, 6゜6'...
・・・・・・・・・LPF, 7・・・・・・Recorder, 8・・・・・・Motor, 9・・・・・・・・・
・Comparator. Patent Applicant Clarion Co., Ltd. Agent Patent Attorney Nagai 1) Takeshi Part 2 Figure 1 Figure 3 Figure 8 Figure 9 One angle change

Claims (2)

[Claims] (1) A first antenna attached to a location other than the center of rotation on the turntable; and a first Doppler frequency signal component extraction means for extracting a Doppler frequency signal component of a radio wave received by the first antenna; a first amplitude limiting means for limiting the amplitude of the Doppler frequency signal component whose amplitude has been limited; a first converting means for converting the frequency fluctuation component of the amplitude limited Doppler frequency signal component into a direct current; A radio wave arrival direction detection device comprising: first carrier component removal means for removing a carrier component. (2) a first antenna attached to a location other than the center of rotation on the turntable; and a first Doppler frequency signal component extraction means for extracting a Doppler frequency signal component of a radio wave received by the first antenna; a first amplitude limiting means for limiting the amplitude of the Doppler frequency signal component whose amplitude has been limited; a first converting means for converting the frequency fluctuation component of the amplitude limited Doppler frequency signal component into a direct current; a first carrier component removal means for removing a carrier component; a second antenna installed at the rotation center position of the turntable; and FM modulation for extracting an FM modulation component of radio waves received by the second antenna. a component extracting means, a second amplitude limiting means for limiting the amplitude of the extracted FM modulated component, a second converting means for converting the amplitude limited FM modulated component into a direct current, and the second converting means. A radio wave characterized by comprising: second carrier component removal means for removing a carrier component from the converted DC signal; and comparison means for comparing both outputs of the first and second carrier component removal means. Arrival direction detection device.