JPH0368354B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an improvement of a Doppler direction finder intended to reduce azimuth measurement errors due to wavefront fluctuations.

[Technical background of the invention]

An example of a conventional Doppler direction finder is shown in FIG. In FIG. 1, the outputs of a plurality of antennas 1-1 to 1-8 (eight antennas are shown as an example in FIG. 1) arranged at equal intervals on the circumference are led to a scanner 2. The scanner 2 has a rotor that is coupled to at least two or more antennas at the same time, and the rotor rotates at a constant speed R times/second to sequentially scan the antennas at a constant speed.

The rotor output of the scanner 2 appears as if one antenna is rotating at a constant speed on the circumference of the array circle, and is therefore subjected to a Doppler shift. The shift frequency Δ is based on the following formula.

Δ= _-0・2πrR/C・sin(2πRt-θ) =−2πrR/λ・sin(2πRt-θ) ……(1) where Δ: Shift frequency (Hz) r: Radius of antenna array circle (m) R: Number of rotations of the scanner (times/second) C: Speed of light (m/second) ₀ : Frequency of the arriving wave (Hz) λ: Wavelength of the arriving wave (m) θ: Azimuth of the arriving wave (radians) This scan A receiver 5 selects and extracts a desired signal from the output signal 3 of the receiver 2, and after passing the intermediate frequency output signal of the receiver 5 through a limiter 6 to remove amplitude modulation components, a frequency discriminator 7 performs frequency discrimination. By doing so, an output voltage proportional to the shift frequency Δ due to the Doppler shift can be obtained.

The output of the frequency discriminator 7 is passed through a narrowband filter 8 to remove components other than the scanning period of the scanner 2, and then full-wave rectified by a rectifier 9, and further passed through an amplitude limiter 1.
0 clamp and supply it to the indicator 11, and the scanner 2
The azimuth angle signal 4 obtained separately from the azimuth angle signal 4 is displayed as the direction of arrival of the radio waves.

[Problems with background technology]

If the wavefront of the radio waves arriving at the antennas 1-1 to 1-8 is an ideal plane wave, no matter how the signal processing is performed, there will always be no azimuth measurement error. However, especially in the short wave band, propagation occurs in the ionosphere, and the wavefront of the radio waves arriving at the antenna always fluctuates. For this reason, the shift frequency has an element of azimuth measurement error Δθ
(t) is entered, and the following equation (2) is obtained with θ ₀ as the true direction of arrival.

Δ=−2πrR／λ・sin [2πRt−{θ ₀ +Δθ(t)}
〓−2πrR／λ・sin(2πRt−θ ₀ )＋2πrR／λ・Δθ(t
)・cos(2πRt-θ ₀ )
...(2) However, |Δθ(t)|〓| In this equation (2), the first term is a component related to the true direction of arrival. The second term is a component related to the direction measurement error caused by wavefront fluctuations, and this term is
It cannot be removed unless it is passed through an infinitely narrow filter that allows only the rotational speed R (Hz) of the scanner 2 to pass.

In practice, a filter with an infinitely narrow band is not used because it takes an infinitely long time for the signal to rise. Therefore, since a band filter with a finite width has to be used, the second term, which is related to the azimuth measurement error, remains to some extent. In particular, if the main frequency of the azimuth measurement error Δθ(t) is less than the rotational speed of the scanner, it will remain almost unchanged.

In the conventional Doppler direction finder shown in FIG. 1, in order to make the displayed waveform on the indicator 11 more sensitive, the demodulator output is full-wave rectified and then clamped, so that only the vicinity of the zero cross of the demodulator output is detected. We are using. Since 2πRt−θ ₀ =0 or π near the zero cross in equation (2), the second term in equation (2), which is related to the azimuth measurement error, appears at the value at the maximum amplitude.

Figure 2 shows a model for analyzing azimuth measurement errors near the zero cross. That is, it is assumed that radio waves arrive from the direction connecting the centers of the i-th and i+1-th antennas to the center of the antenna array among the N antennas arranged on the circumference of a radius r. Therefore, the ideal wavefront A of radio waves is antenna i and antenna i
It becomes parallel to the straight line connecting +1.

Here, we will consider a case where wavefront fluctuation occurs and a phase advance θ ₁ of α radians occurs on the antenna i+1 side, as shown by the solid line (actual wavefront) in FIG. 2. The shift frequency Δ' due to fluctuation is the amount of phase change (radian)/(2π·time), and is expressed as follows.

Therefore, the direction measurement error Δθ(t) is 2πRt in equation (2).
-θ ₀ =0, and it is determined as follows.

Δθ(t)Nλ/4π ² r・α ……(4) On the other hand, in the case of the Adkotsk type direction finder, the distance between the opposing antennas is equal to the distance between adjacent antennas of the Doppler type direction finder, The orientation measurement error Δθ _a (t) for the model is expressed by the following equation (5).

Δθ _a (t)λ/2πD・α ...(5) Now, taking into consideration the relationship of D2πr/N and finding the ratio of equation (4) to equation (5), we get the following equation (6). become that way.

Δθ(t)/Δθ _a (t)Nλ/4π ² r・α/λ/2π
・N/2πr・α=Nλ/4π ² r・α/Nλ/4π ² r・α=1
...(6) As a result, it can be seen that the Doppler direction finder azimuth measurement error by the conventional Doppler direction finder is the same as that of the Adkotsu direction finder in which the distance between adjacent antennas is the diameter of the array circle.

[Purpose of the invention]

The present invention has been made to eliminate the above-mentioned conventional drawbacks, and an object of the present invention is to provide a Doppler type direction finder that can reduce azimuth measurement errors caused by wavefront fluctuations as much as possible.

[Summary of the invention]

The Doppler direction finder of the present invention uses a scanner to sequentially scan the outputs of multiple antennas arranged at equal intervals on the circumference at a constant speed, and a receiver selects a predetermined signal from the output signals of the scanner. After the amplitude modulation component of the intermediate frequency output signal is removed by a limiter, the Doppler shift is detected by a frequency discriminator, and the sine and cosine signals are generated by a sine-cosine generator based on the azimuth signal generated by the scanner. The sine signal, cosine signal, and the output of the frequency discriminator are multiplied by a multiplier, and the scanning period components of the scanner included in the output of this multiplier are removed by a low-pass filter. The display means displays the DC voltage component corresponding to the arrival method.

[Embodiments of the invention]

Embodiments of the Doppler direction finder of the present invention will be described below with reference to the drawings. FIG. 3 is a block diagram showing the configuration of one embodiment. This third
In the figure, the same parts as in FIG. 1 are given the same reference numerals and described. In this embodiment as well, the number of antennas will be described as eight, similar to FIG.

Eight antennas 1-1 to 1- at equal intervals on the circumference
8 are arranged, and these antennas 1-1 to 1-
The output of 8 is guided to a scanner 2, which has a rotor coupled to at least two or more antennas at the same time. The rotor rotates at a constant speed R times/second and scans the antenna sequentially at a constant speed. The output of this rotor, ie the output 3 of the scanning base 2, is applied to a receiver 5. The intermediate frequency output signal obtained by this receiver 5 is sent to a frequency discriminator 7 through a limiter 6. The output of this frequency discriminator 7 is supplied to multipliers 12-1 and 12-2.

The scanner 2 also outputs an azimuth signal 4, and this azimuth signal 4 is sent to the sine-cosine generator 1.
3. This sine cosine generator 13
sine signal 14 and cosine signal 15 from
are supplied to multipliers 12-1 and 12-2, respectively, and multiplied by the output of frequency discriminator 7, respectively.

The output of the multiplier 12-1 is sent to the low-pass filter 16-1.
The signal is sent to the multiplier 17-1 through the multiplier 17-1. Similarly, the output of multiplier 12-2 is transmitted to low-pass filter 16-2.
2 to the multiplier 17-2. The multipliers 17-1 and 17-2 each have an oscillator 18
The output of is also supplied.

Therefore, multipliers 17-1 and 17-2 output the output of oscillator 18 and low-pass filters 16-1 and 17-2, respectively.
Multiply the output of 16-2 and send the multiplication result to XT.
Output to scope 19. XT Scope 19 X
The output of the multiplier 17-2 is added to the axis, and the output of the multiplier 17-1 is added to the Y-axis of the XT scope 19.

Next, the operation of the Doppler type direction finder of the present invention configured as above will be explained. In explaining the operation, the operation of the system from the antennas 1-1 to 1-8 to the frequency discriminator 7 is the same as that shown in FIG. 1, and the explanation thereof will be omitted here.

The frequency discriminator 7 inputting the output of the limiter 6 divides the output proportional to the shift frequency Δ shown in equation (1) above into two and outputs the divided output to the multipliers 12-1 and 12-2.

On the other hand, the azimuth signal 4 obtained from the scanner 2 is input to a sine/cosine generator 13, which outputs a sine signal 14 and a cosine signal 15. Sine signal 14 is sent to multiplier 12-1, and cosine signal 15 is sent to multiplier 12-2.

In the multiplier 12-1, the output of the frequency discriminator 7 and -
Multiply by sin(2πRt), and multiplier 12
-2 multiplies the output of the frequency discriminator 7 by cos(2πRt). The sine signal 14 and cosine signal 15 used here are generated by a sine-cosine generator 13 based on the azimuth signal 4 obtained from the scanner 2.
Output V ₁ of multiplier 12-1 and multiplier 12-2
The output V ₂ of is calculated as follows using equation (1).

V ₁ =K・Δ・{−sin(2πRt)}=KπrR/λ
・{cos(θ)−cos(4πRt−θ)}……(7) V ₂ =K・Δ・cos(2πRt)=KπrR/λ・{si
n(θ)−sin(4πRt−θ)}……(8) where K: proportional constant The output of multipliers 12-1 and 12-2 is filtered by a low-pass filter 1 with a cutoff below the frequency R (Hz).
By passing through 6-1 and 16-2, the above (7)
The second term in { } of Equations and Equations (8), that is, the component related to the scanning period of the scanner 2, disappears, and only the first term, that is, the DC voltage component related to the direction of arrival θ of the radio wave, remains. By supplying this to the XY scope 19, the radio wave arrival direction can be displayed as one bright spot. The outputs of the low-pass filters 16-1 and 16-2 are approximately direct current signals, and are suitable as signals for supplying azimuth measurement results to multiple devices.

In the embodiment shown in FIG. 3, the radio wave arrival direction is displayed as a straight line extending from the center of the display surface of the XY scope 19, and the low-pass filters 16-1 and 1
The output of the oscillator 6-2 is multiplied by a signal obtained from the oscillator 18, for example, A=2/1 {1+cos(ωt)} (9) by the multipliers 17-1 and 17-2. If the outputs of the low-pass filters 16-1 and 16-2 are multiplied by the output of the oscillator 18 in this way, compared to the case where the output of the frequency discriminator 7 is multiplied by the oscillator 18, the output frequency of the low-pass filter will depend on the output frequency of the oscillator. The cutoff frequencies of 16-1 and 16-2 are not limited, and an increase in azimuth measurement errors can be avoided.

However, the demodulator output signal containing the azimuth measurement error due to wavefront fluctuation is already shown in equation (2). Therefore, in this case, the outputs V ₁ and V ₂ of the multipliers 12-1 and 12-2 are as follows.

V ₁ =KΔ{−sin(2πRt)}〓KπrR／λ{cos(
θ ₀ )−Δθ(t)sin(θ ₀ )} −KπrR／λ{cos(4πRt−θ ₀ )+Δθ(t)s
in(4πRt−θ ₀ )}……(10) V ₂ =KΔcos(2πRt)〓KπrR／λ{sin(θ ₀ )
−Δθ(t)cos(θ ₀ )} −KπrR／λ{sin(4πRt−θ ₀ )+Δθ(t)c
os(4πRt−θ ₀ )}……(11) The outputs V ₃ and V ₄ of the low-pass filters 16-1 and 16-2 for this signal are as follows: The second terms of equations (10) and (11) disappear, Equivalent integration over the time of one rotation of the scanner 2 is performed by the rise characteristic of the low-pass filter, and the following is obtained.

V ₃ KπrR／λ1/1/R∫ ^1/R ₀ {cos(θ ₀ )
−Δθ(t) sin(θ ₀ )}dt……(12) V ₄ KπrR／λ1/1/R∫ ^1/R ₀ {sin(θ ₀ )
−Δθ(t) cos(θ ₀ )}dt...(13) Up until now, the effect of scanner 2 has been equivalent to 1
It was assumed that the book antenna rotates on the circumference of the array at R times/second, but when examining the effect of wavefront fluctuation, the phase difference for each antenna becomes a problem. , the above-mentioned integration with respect to time is inappropriate and should be considered as a sum for each antenna. Therefore, the following representation is appropriate.

V ₃ KπrR/λ1/N _N 〓 ⁱ⁼¹ {cos(θ ₀ )−Δθ(ti)・sin(θ ₀ )} =KπrR/λ{cos(θ ₀ )−sin(θ ₀ )1/
N _N 〓 ⁱ⁼¹ Δθ(ti)} ...(14) V ₄ KπrR／λ1/N _N 〓 ⁱ⁼¹ {sin(θ ₀ )＋Δθ(ti)cos(θ ₀ )} =KπrR／λ{sin (θ ₀ )+cos(θ ₀ )1/
N _N 〓 ⁱ⁼¹ Δθ(ti)} ...(15) The display orientation φ on the XY scope 19 obtained from these two signals is φ=θ ₀ +1/N _N 〓 ⁱ⁼¹ Δθ(ti)... …(16) becomes. Assuming that the deviation from the true bearing, that is, the element of bearing measurement error Δθ(t), is normally distributed with a standard deviation of Δθ, the standard deviation Δφ of the displayed bearing error shown in equation (10) is as follows. .

Δφ=1/N√ Δθ=Δθ/√N (17) Whereas the standard deviation of the display orientation error in conventional signal processing is Δθ, in this invention it is 1/
has decreased to √. This is due to the effect of utilizing all of the antennas.

〔Effect of the invention〕

As described above, according to the Doppler type direction finder of the present invention, the outputs of a plurality of antennas arranged at equal intervals on the circumference are sequentially scanned by a scanner at a constant speed, and the output signals of the scanner are After selecting a predetermined signal with a receiver and removing the amplitude variation component of the intermediate frequency output signal with a limiter, the Doppler shift is detected with a frequency discriminator and a sine signal is generated based on the azimuth signal generated with a scanner. A sine-cosine generator generates a cosine signal, and a multiplier multiplies the sine signal, cosine signal, and the output of the frequency discriminator, respectively, and the scanning period component of the scanner included in the output of this multiplier is calculated separately. After removing it with a reduction filter, the DC voltage component relative to the radio wave arrival direction is displayed on the display means, so all the signals of the scanner output are effectively used to average the direction measurement error over the entire circumference. , the direction measurement error caused by wavefront fluctuation is reduced to 1/1 compared to conventional methods.
It can be reduced to √(N: number of antennas). If the number of antennas is 8, it is 1/2.83.
In the case of 24 units, the improvement to 1/4.90 is enormous.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an example of a conventional Doppler type direction finder, Fig. 2 is a diagram showing an analytical model for the direction measurement error of the Doppler type direction finder shown in Fig. 1, and Fig. 3
The figure is a block diagram showing one embodiment of the Doppler type direction finder of the present invention. 1-1 to 1-8... antenna, 2... scanner,
5... Receiver, 6... Limiter, 7... Frequency discriminator, 12-1, 12-2, 17-1, 17-2
... Multiplier, 13 ... Sine cosine generator, 1
6-1, 16-2...low-pass filter, 18...oscillator, 19...XY scope.

Claims (1)

[Claims] 1. A plurality of antennas arranged at equal intervals on the circumference, a scanner that sequentially scans the output of these antennas at a constant speed, a receiver that selects a desired signal from the output signals of this scanner, and this receiver. a limiter that removes the amplitude modulation component of the intermediate frequency output signal of the scanner, a frequency discriminator that receives the output of this limiter and detects the frequency deviation due to Doppler shift, and a sine signal and a a sine cosine generator that generates a cosine signal; a first multiplier that multiplies the sine signal by the output of the frequency discriminator; and a second multiplier that multiplies the cosine signal and the output of the frequency discriminator. , a low-pass filter that is connected to each of the first and second multipliers and removes a scanning period component of the scanner included in the output of the multiplier; and an output direction of the radio wave is displayed by the output of the low-pass filter. A Doppler direction finder consisting of means and means.