JP4564407B2 - Antenna device - Google Patents

Description

  The present invention relates to an antenna device used in, for example, a radar system, and more particularly to a technique for removing mixing of signals other than desired signals.

  For example, Patent Document 1 discloses a radar signal processing device that employs a pulse compression method used in a radar device. This radar signal processing apparatus transmits a chirp signal (linear FM modulation signal) as a transmission signal toward a moving target that moves relatively, receives the reflected signal reflected by the moving target as a received signal, and then receives the received signal. The Doppler component resulting from the movement of the target is extracted, and the moving target is detected based on the extracted Doppler component.

  In the pulse compression method, a long pulse is transmitted as a modulated signal, and after reception, a short pulse signal with improved S / N is obtained via a pulse compression filter that matches the modulated pulse signal. It has been applied to many radars because of its advantages such as extending the detection distance by increasing energy, realizing high range resolution, and effective in suppressing interference and jamming waves.

The performance of such a conventional radar device (chirp radar device) is generally the waveform after pulse compression processing (output waveform), specifically, the main lobe pulse width (main lobe width) and the side lobe level (side (Lobe level) and the S / N loss at the peak value of the main lobe.
JP-A-4-357485

  By the way, as in the conventional radar device described above, it is strongly recommended that the antenna device itself removes radio wave interference and unwanted waves, rather than improving the performance of the radar device by processing the signal obtained from the antenna device. It has been demanded.

  However, since the conventional antenna device has a relatively high side lobe, it is inevitable to mix other signals. In order to suppress this side lobe, various window functions such as a hamming window are generally used for weighting. However, as the side lobe is suppressed, the antenna gain decreases and the sensitivity to the signal to be measured is impaired. There was a problem.

  Qualitatively, this tendency is unavoidable, but the window function known in the past does not guarantee that the filter has the least signal loss to achieve the sidelobe level to be realized, so it is realized. It was just a window function option that was guaranteed to be possible, so the critical performance was unknown.

  The present invention has been made in order to solve the above-described problems, and an object of the present invention is to provide an antenna device capable of realizing a side lobe free (zero side lobe) and obtaining a high antenna gain. is there.

In order to solve the above-described problems, the present invention provides an antenna device including a plurality of antenna elements, wherein the antenna pattern includes the antenna pattern with respect to the outer direction except for the central direction of the main lobe of the antenna pattern and a plurality of directions in the vicinity thereof. A weight calculation unit that calculates a weighting function that maximizes the antenna gain while setting the side lobe of the antenna pattern to zero, a weight calculation unit that calculates a weight vector using the weighting function, and a plurality of weight vectors calculated by the weight calculation unit, a plurality of multipliers for weighting each of the plurality of signals obtained from the antenna elements, e Bei a combiner for combining the outputs of the plurality of multipliers, the weight calculation unit, the weighting function

  According to the present invention, a window function to be applied to a spatial filter such as an antenna, which realizes sidelobe free (zero sidelobe) and at the same time, calculates a window function that theoretically maximizes the antenna gain, is calculated. By using the window function thus made as a weighting function of the antenna element, it is possible to realize a high-performance antenna device that can highly eliminate mixing of other signals that could not be realized in the past and obtain a high antenna gain.

  Hereinafter, an antenna device according to an embodiment of the present invention will be described in detail with reference to the drawings.

  First, an outline of a radar apparatus to which the antenna apparatus according to the first embodiment of the present invention is applied will be described with reference to the block diagram shown in FIG.

  The radar apparatus includes a transmission signal generator 10, a D / A conversion unit 11, a local oscillator 12, a transmission side mixer 13, a transmission signal amplifier 14, a circulator 15, an antenna 16, a reception signal amplifier 17, a reception side mixer 18, and an A / A. It comprises a D conversion unit 19, a pulse compression processing unit 20, a frequency analysis processing unit 21, and a target detection processing unit 22.

  The transmission signal generator 10 generates a transmission signal and sends it to the D / A converter 11. The D / A converter 11 converts the transmission signal from the transmission signal generator 10 into an analog signal and sends it to the transmission side mixer 13. The local oscillator 12 generates a local signal having a local frequency and sends it to the transmission side mixer 13 and the reception side mixer 18. The transmission-side mixer 13 converts the transmission signal into a high-frequency signal by mixing the transmission signal from the D / A converter 11 and the local signal from the local oscillator 12, and sends it to the transmission signal amplifier 14.

  The transmission signal amplifier 14 amplifies the high frequency signal from the transmission side mixer 13 to a predetermined level and sends it to the circulator 15. The circulator 15 switches between outputting a high-frequency signal from the transmission signal amplifier 14 to the antenna 16 or outputting a reception signal from the antenna 16 to the reception signal amplifier 17.

  The antenna 16 corresponds to the antenna device of the present invention, and is composed of an array antenna in which a plurality of antenna elements are arranged in a line. The antenna 16 transmits a high-frequency signal sent from the transmission signal amplifier 14 via the circulator 15 toward the target, receives a reflected wave from the target, and sends it to the circulator 15 as a received signal.

  The reception signal amplifier 17 amplifies the reception signal sent from the antenna 16 via the circulator 15 with low noise and sends it to the reception side mixer 18. The reception-side mixer 18 converts the reception signal from the reception signal amplifier 17 and the local signal from the local oscillator 12 to convert the reception signal into an intermediate frequency signal (IF signal) and sends it to the A / D conversion unit 19. . The A / D conversion unit 19 converts the IF signal from the reception-side mixer 18 into a digital signal and sends the digital signal to the pulse compression processing unit 20.

  The pulse compression processing unit 20 performs pulse compression processing on the digital signal from the A / D conversion unit 19. The result of the pulse compression processing in the pulse compression processing unit 20 is sent to the frequency analysis processing unit 21.

  The frequency analysis processing unit 21 performs frequency analysis processing on the signal from the pulse compression processing unit 20. Specifically, time domain data is converted to frequency domain data by Fourier transforming the signal from the pulse compression processing unit 20. That is, in order to detect the target relative speed, the received signal is decomposed into a Doppler component which is a target speed component. The Doppler component obtained in the frequency analysis processing unit 21 is sent to the target detection processing unit 22. The target detection processing unit 22 extracts the movement target by extracting the Doppler component from the frequency analysis processing unit 21.

  Next, details of the antenna device (corresponding to the antenna 16 in FIG. 1) according to the first embodiment of the present invention will be described.

  FIG. 2 is a block diagram showing a detailed configuration of the antenna 16. The antenna 16 includes a plurality of antenna elements 1, a weight calculation unit 2, a plurality of multipliers 3 and a combiner 4 provided corresponding to the plurality of antenna elements 1. As will be described in detail later, the weight calculation unit 2 calculates a weight vector Wm and sends it to a plurality of multipliers 3. The plurality of multipliers 3 multiply the signals sent from the plurality of antenna elements 1 by the weight vectors Wm sent from the weight calculation unit 2, and send the multiplication results to the synthesizer 4. The synthesizer 4 synthesizes the signals sent from the plurality of multipliers 3 and sends them to the circulator 15 (see FIG. 1).

  Hereinafter, the calculation method of the weight vector Wm in the weight calculation unit 2 will be described focusing on derivation of a window function that realizes sidelobe free and theoretically maximizes the antenna gain.

Here, a one-dimensional array antenna is assumed as the antenna device, and the next vector having N elements is defined as a weight vector W representing the amplitude / phase distribution of the antenna aperture plane.

Here, the total number N of weight vectors indicates the total number of elements on the antenna aperture. The antenna pattern output in response to this can be expressed as follows as a vector y having each angle direction on the angle axis as an element.

Here, d: element spacing λ: antenna pattern output (antenna gain) with respect to an angle θ that is a wavelength.

At this time, the following relationship is established between the weight vector W and the antenna pattern vector y.

  Using the definitions shown above, a method for calculating the antenna aperture plane distribution that is free of side lobes will be described below.

  In general, weighting by a window function is used to reduce the side lobe, but its shape makes the weight at the end of the opening lighter than the weight near the center of the opening. Therefore, it is known that, in order to reduce the side lobe, the 3 dB width is narrowed and the main beam width is widened as compared with the amplitude distribution 3 dB width of the opening surface. Considering the number of elements corresponding to this 3 dB width as the number of effective elements in the weighting, there is a strong correlation between the number of effective elements and the main beam width. Conversely, if the number of effective elements is constrained, the main beam width is widened, but the degree of freedom for controlling the side lobe can be obtained as shown below.

Here, for all the elements N on the antenna aperture, by setting the initial state as the number of effective elements for the central portion _Ne element as shown in FIG. 3, a sidelobe-free antenna aperture distribution can be derived. Indicates.

First, the antenna pattern output considering that the aperture corresponding to the effective element is rectangular in the center of the weight vector, that is, the weight is zero outside the effective aperture, is calculated using the following weight vector: it can.

For the antenna pattern vector y calculated by the above equation, only angle sample output up to ± N _x near the main lobe when the peak direction of the antenna pattern is K is allowed, and sample values in all other directions ( An antenna pattern vector with a constraint condition of 0 corresponding to a side lobe is defined as follows.

This antenna pattern vector indicates an antenna pattern in which all side lobes other than the main lobe are 0. If W _m satisfying the following equation is feasible, the W _m is a weight vector to be obtained. .

  Although the weight vector to be obtained (corresponding to the aperture distribution) is formulated, it is generally considered that such a window function with a constraint condition causes the aperture efficiency to be extremely deteriorated and the antenna gain to decrease. The antenna pattern formation principle for theoretically deriving a window function that maximizes the antenna gain under the sidelobe-free constraint condition is shown below.

First, the antenna aperture plane distribution that maximizes the antenna gain is the same as the condition that maximizes the output S / N for the incident signal from the peak direction of the main lobe, and this output S / N is defined as follows. it can.

Indicates. K is a design parameter that determines the peak direction of the antenna pattern. Therefore, the output S / N with respect to the incident signal from the peak direction can be expressed by the following equation.

  Since the maximum gain condition including the constraint condition cannot be directly calculated in this form, the following identity is newly defined.

First, it is necessary to satisfy the following conditional expression in order for Expression (9) to hold simultaneously under the condition of Expression (7).

Further, the following identity is introduced for the constraint on the number of effective elements assumed in the equation (7).

By using the identity shown above, equation (14) can be transformed into the following form.

At this time, the noise output of equation (10) can be modified as follows.

Similarly, the signal output of equation (11) can be expressed as follows.

  Here we apply the following Schwartz inequality:

About vectors F and G

Therefore, the following redefinition

The conditions for maximizing the output S / N can be derived as follows.

Note that the condition for establishing the equal sign that maximizes the output S / N, that is, the antenna gain is given by the following equation.

The condition under which the calculated antenna gain becomes maximum is the maximum condition in the constraint conditions shown in the previous section, and W calculated here corresponds to a conditional expression for satisfying the maximum gain. Therefore, the weight vector W _m corresponding to the actual aperture distribution can be converted to W _{m according} to Equation (18) using W calculated here, whereby the S / N maximum weight vector with zero side lobe can be calculated. The result is as follows.

Furthermore, since the equation (32) includes a steering vector indicating the peak direction, the shape H (excluding a constant term) of the window function, which is an aperture weight excluding the steering vector, can be expressed by the following equation. I understand.

  The weight vector obtained by the above derivation has a main beam width approximately equivalent to the number of initially set effective elements, is a sidelobe-free constraint condition, and an aperture distribution with maximum gain under this condition, and a convergence calculation It can be seen that it can be directly calculated regardless of the above.

In the above description, a case has been described in which only the angular sample output up to ± N _{x in the} vicinity of the main lobe of the antenna pattern is allowed and the sample values in all other directions are restricted to zero. It is also possible to easily constrain the sample values in some other directions to 0 while allowing only angle sample output up to ± N _x near the main lobe of the pattern.

  The antenna device according to the first embodiment described above is assumed to be a one-dimensional array antenna. For example, as shown in FIG. 4, the antenna elements 1 are arranged in the azimuth direction and the elevation direction. It can also be applied to a two-dimensional array antenna. In this case, the weight vector can be calculated for a plurality of antenna elements in the azimuth direction or a plurality of antenna elements in the elevation angle direction.

Further, the method described here is not limited to the case where the effective elements are continuous in the center. As shown in FIG. 5, the effective elements are distributed and arranged in the sub-antennas having a plurality of small apertures. The weighting function can also be calculated when a distributed array is configured or when the number of N _x is not equal on the left and right with respect to the main lobe peak direction.

  Further, after calculating the weight vector generated using the weight function obtained by the above-described method, the output of the combiner 4 calculated using the weight vector is used as the weight calculation unit 2 as shown in FIG. In the weight calculation unit 2, the antenna pattern is changed so as to further reduce the side lobe based on the data fed back from the combiner 4, and the weight vector is calculated again using the above-described weighting function. Can be configured to repeat. According to this configuration, the side lobe can be reduced to a desired level, and a high antenna gain can be obtained.

  The present invention is applicable to a radar apparatus or the like that employs a pulse compression method.

It is a block diagram which shows the structure of the radar apparatus with which the antenna apparatus which concerns on the 1st Embodiment of this invention was applied. It is a block diagram which shows the structure of the antenna as an antenna apparatus which concerns on the 1st Embodiment of this invention. In the antenna apparatus which concerns on the 1st Embodiment of this invention, it is a figure for demonstrating the number of effective elements with respect to the total number of elements on an antenna opening. It is a figure which shows the example in case a two-dimensional array antenna is used as an antenna apparatus which concerns on the 1st Embodiment of this invention. It is a figure for demonstrating the case where the antenna apparatus which concerns on the 1st Embodiment of this invention is made into the distributed array structure by the some subantenna. It is a block diagram which shows the structure of the antenna as an antenna apparatus which concerns on the modification of the 1st Embodiment of this invention.

Explanation of symbols

1 Multiple antenna elements 2 Weight calculation unit 3 Multiple multipliers 4 Synthesizer

Claims (5)

An antenna device including a plurality of antenna elements,
Except for the central direction of the main lobe of the antenna pattern and a plurality of directions in the vicinity thereof, a weighting function that maximizes the antenna gain at the same time as the side lobe of the antenna pattern with respect to the outer direction is calculated and used. A weight calculation unit for calculating a weight vector using
A plurality of multipliers each weighting a plurality of signals obtained from the plurality of antenna elements using the weight vector calculated by the weight calculation unit;
A combiner for combining the outputs of the plurality of multipliers;
Bei to give a,
The weight calculation unit includes the weighting function.

The plurality of antenna elements are composed of a plurality of antenna elements arranged in the azimuth direction and a plurality of antenna elements arranged in the elevation angle direction,
The plurality of multipliers are a plurality of signals obtained from a plurality of antenna elements arranged in the azimuth direction or a plurality of antennas arranged in the elevation angle direction using the weight vector calculated by the weight calculation unit. 2. The antenna device according to claim 1, wherein each of a plurality of signals obtained from the elements is weighted. An antenna device that constitutes a distributed array in which a plurality of sub-antennas each having a plurality of antenna elements are distributed and arranged,
  Each of the plurality of sub-antennas is
  Except for the central direction of the main lobe of the antenna pattern and a plurality of directions in the vicinity thereof, the weighting function is calculated by calculating the weighting function which makes the side lobe of the antenna pattern with respect to the outside direction zero and at the same time maximizes the antenna gain. A weight calculation unit for calculating a weight vector using
  A plurality of multipliers each weighting a plurality of signals obtained from the plurality of antenna elements using the weight vector calculated by the weight calculation unit;
  A combiner for combining the outputs of the plurality of multipliers;
With
  The weight calculation unit includes the weighting function.

The weight calculation unit changes an antenna pattern so as to further reduce the side lobe based on an output of the combiner, and recalculates a weight vector using the weighting function. The antenna device described. The plurality of antenna elements constituting the sub-antenna is composed of a plurality of antenna elements arranged in the azimuth direction and a plurality of antenna elements arranged in the elevation direction,
  The plurality of multipliers are a plurality of signals obtained from a plurality of antenna elements arranged in the azimuth direction, or a plurality of antennas arranged in the elevation angle direction, using the weight vector calculated by the weight calculation unit. 5. The antenna device according to claim 3, wherein each of a plurality of signals obtained from the elements is weighted.

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