JP2008003078A - Transmission signal generator and radar transmission device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transmission signal generator that suppresses a spurious component and makes the signal level of center frequency maximum. <P>SOLUTION: A transmission signal generator 10 has a window function calculator 31 for generating a window function that makes all frequencies on its outside without a center frequency of an input signal and its adjacent frequencies zero and makes the signal to output S/N of the center frequency maximum, and a transmission signal generator 32 for generating a transmission signal whose amplitude is modulated in a shape of an envelope curve based on the window function generated by the window function calculator 31. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a transmission signal generator that generates a transmission signal and a radar transmission device using the transmission signal generator.

  In recent years, with the use of radio waves increasing, it is strongly required to narrow the radar band in order to efficiently use frequencies with other devices.

  At the same time, suppressing the spurious component of the radar as much as possible is an international issue. As described above, if the radar can be operated with a narrower frequency bandwidth by developing a technology for narrowing the bandwidth of the radar and reducing the spurious component, it is possible to contribute to eliminating the tightness of the frequency resources.

  One solution to these problems is the practical application of low-power pulse compression radar.

  Patent Document 1 discloses a radar signal processing apparatus that employs a pulse compression method. 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 such a pulse compression method, a signal modulated in a long pulse is transmitted, and after reception, the S / N ratio (Signal to Noise Ratio: hereinafter, SNR) is improved through a pulse compression filter suitable for the modulated signal in the pulse. It is applied to many radars because of its advantages such as extending the detection distance, realizing high distance resolution, and effective in suppressing interference / jamming waves.
JP-A-4-357485

  In the above pulse compression radar apparatus, a chirp signal, a phase code modulation signal, or the like is used as a transmission signal. These signals have low side lobes after pulse compression, but have a wide spectrum and spurious components. There are also many.

  In order to reduce the spurious component, it has been studied to taper the edge portion of the waveform of the transmission signal. However, as the spurious component is suppressed, the fundamental characteristics of the radar such as range resolution are impaired, and the signal level is reduced. It will decline.

  Although such a trade-off relationship cannot be completely eliminated, it seems possible to show the limit of narrowing that can be achieved while maintaining the signal level with respect to the spurious level to be realized. However, there is no conventional method that shows this, and the performance limit that can be realized is unknown.

  An object of the present invention is to provide a transmission signal generator capable of suppressing spurious components of a transmission signal and maximizing the signal level of the center frequency of the transmission signal, and a radar transmitter using the transmission signal generator.

  In order to solve the above-mentioned problem, the transmission signal generator of the present invention sets the frequency outside the center of the input signal to zero except for the center frequency and some frequencies in the vicinity thereof, and at the same time, the center frequency. A window function calculation unit that generates a window function that maximizes the SNR with respect to and a transmission signal generation unit that generates a transmission signal that is amplitude-modulated based on the window function generated by the window function calculation unit It is characterized by that.

  According to the transmission signal generator of the present invention, the window function is such that all the frequencies outside the center frequency and a part of the frequency in the vicinity thereof are set to zero and the output S / N with respect to the center frequency is maximized at the same time. Since a transmission signal with amplitude modulation is generated based on the above, spurious components can be suppressed and the signal level of the center frequency can be maximized. Therefore, if this transmission signal generator is applied to a transmitter of a lator system, it is possible to realize a narrow band of radar.

  Hereinafter, a transmission signal generator according to an embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a block diagram showing an outline of a radar apparatus to which a transmission signal generator according to an embodiment of the present invention is applied.

  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 as a digital signal (pulse 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 signal level, and sends it to the circulator 15. The circulator 15 switches between outputting the high-frequency signal from the transmission signal amplifier 14 to the antenna 16 or outputting the reception signal from the antenna 16 to the reception signal amplifier 17.

  The antenna 16 is composed of, for example, an array antenna or the like. The antenna 16 transmits a high-frequency signal transmitted from the transmission signal amplifier 14 via the circulator 15 toward the target, receives a reflected wave from the target, and receives a received signal. To the circulator 15.

  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 frequency analysis processing unit 21 converts time domain data into frequency domain data by performing Fourier transform on the signal compressed by the pulse compression processing unit 20. Then, in order to detect the target relative speed, the received signal is decomposed into a Doppler component which is a target speed component. 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 transmission signal generator 10 according to the present embodiment will be described.

  FIG. 2 is a block diagram showing a detailed configuration of the transmission signal generator 10. The transmission signal generator 10 includes a window function calculation unit 31 and a transmission signal generation unit 32.

  The window function calculation unit 31 sets the frequency outside the center of the input signal (phase-modulated rectangular pulse) to zero except for the center frequency and a part of the frequency in the vicinity thereof, and at the same time with respect to the center frequency. A window function H that maximizes the SNR is generated, and the generated window function H is sent to the transmission signal generator 32. Details of the window function calculation unit 31 will be described later.

  The transmission signal generator 32 generates a transmission signal in which the amplitude of the input signal is modulated by the window function H sent from the window function calculator 31.

  Hereinafter, a method for generating a transmission signal will be described focusing on derivation of the window function H in the window function calculation unit 31.

<Principle of transmission signal formation to be spurious free>
Hereinafter, a calculation method of the window function H that theoretically realizes the minimum filter loss under the constraint condition of spurious free will be described.

First, the weight vector W corresponding to the data obtained by sampling the transmission pulse is

I will write.

Here, the subscript “N _f ” represents the total number of samples of the transmission pulse for a certain opening time.

Then, the frequency spectrum for this data is set as a vector y of a spectrum pattern having the output at each frequency (discrete sample point) on the frequency axis as an element,

I will write.

At this time, between the weight vector W and the frequency vector y,

The relationship holds. Here, “Q” represents a fast Fourier transform matrix (FFT matrix), and n, k = 1, 2,..., N _f . Note that “N _f ” defined above also represents the number of FFT points. In addition, the subscript “T” in Expression (3) represents transposition.

From equation (4), the inverse fast Fourier transform matrix (IFFT matrix) is

It can be calculated as follows. Here, “*” represents a complex conjugate.

  It should be noted that the spectral pattern obtained by convolving the spectral pattern calculated by Equation (3) with the spectral pattern of the input pulse is observed.

  Here, it is assumed that a transmission pulse width that satisfies a predetermined basic performance such as range resolution is effective data and exists in the central region of the weight vector W as shown in FIG.

At this time, the weight vector W _m that makes the output from the spurious frequency domain zero and maximizes the SNR of the center frequency is

Can be written. Here, “S” is a steering vector representing the center frequency.

Accordingly, the window function H (excluding the constant term) that is the weight of the aperture surface excluding the steering vector S is

It is expressed.

  For reference, the derivation process of equations (7) to (9) will be described in detail below.

(1) Filter formation principle to be spurious free First, as shown in FIG. 3, when the data outside the effective data is set to zero, the weight vector is

It is written. Furthermore, the frequency vector that allows only the output at the frequency sample points from the main lobe of the frequency filter, which is the center frequency, to ± N _x and sets the output at the other frequency sample points to zero as the side lobe is

It is written. Here, K is a frequency filter number which is a center frequency.

At this time, between the weight vector W _s and the frequency vector y _m is

The relationship holds.

As described above, the frequency vector y _m, since illustrates a spectral pattern that all side lobes other than the main lobe near becomes 0, in equation (3), and a y = y _m Formula

The weight vector W = W _m satisfying the _above becomes the target weight vector. Considering equation (12) as a constraint on equation (14),

Is obtained. From this, the weight vector W _{m to} be obtained is

Can be written.

(2) Principle of filter output maximization SNR is a numerical value (unit: dB) indicating the ratio of noise contained in the output signal.

It is expressed. “S” is a vector representing a sample value sequence of the input signal corresponding to the center frequency of the frequency filter,

It is written.

In order to obtain the weight vector W _m that maximizes the SNR expressed by the equation (17) under the above constraint condition (side lobe-free condition), the identity equation

Is introduced.

Than this,

Get.

Using equation (22), equation (16) becomes

It can be deformed as follows. At this time, the denominator (noise output) of Equation (17) is

It is transformed as follows. Similarly, the numerator (signal output) of equation (17) is

It can be deformed as follows.

Where the redefined vector

And Schwartz's inequality for arbitrary vectors F and G

Is applied to equation (17), equation (17) is transformed as follows:

The SNR is maximized when the equal sign is established in the equation (31).

As given. Here, α is a constant.

(3) Derivation results of sidelobe-free filter coefficients By substituting equation (29) into equation (32),

Get. Substituting equation (33) into equation (16), the weight vector W _{m to} be obtained is

As obtained.

  The window function H obtained in this way is a weight matrix having a filter bandwidth substantially corresponding to the initially set number of valid data and maximizing the SNR under the sidelobe-free condition. Further, as apparent from the above calculation process, the above calculation can be directly calculated regardless of the convergence calculation.

  By using the window function H obtained in this way, it becomes possible to obtain a transmission signal in which the spurious component is suppressed while maximizing the SNR of the center frequency from the input signal. That is, according to the transmission signal generator 10 of the present invention, the signal level can be secured by minimizing the signal loss at the center frequency, and the frequency band can be narrowed.

In the above example, the waveform of the input signal of the total number of data N _f having a predetermined center frequency is set as the original waveform, and the original waveform is set as the steering vector S, and then the window function H is applied to the transmission signal. Although the corresponding weight vector W is generated, the window function calculated in advance by the above procedure can be stored in a storage unit (not shown).

  It is also possible to use a signal having a constant frequency as an original waveform, and it is also possible to use a waveform subjected to frequency modulation such as a chirp signal as an original waveform. Furthermore, it is also possible to transmit a plurality of pulse trains obtained by phase-modulating the waveform amplitude-modulated by the window function in this manner for each pulse continuously or intermittently.

  As described above, the transmission signal generator 10 according to the present embodiment sets all the frequencies outside the center signal to zero except for the center frequency of the input signal and some nearby frequencies, and maximizes the output SNR with respect to the center frequency. And a transmission signal generation unit 32 that generates a transmission signal obtained by modulating the amplitude of the input signal into an envelope shape based on the calculated window function. .

  Therefore, it is possible to generate a transmission signal that suppresses spurious components and maximizes the signal level of the center frequency.

  If it is difficult to directly generate a transmission signal, the transmission signal of the transmission signal generator 10 can be converted to a required center frequency by frequency conversion to a higher frequency. FIG. 4 shows the configuration of a radar transmitter that enables such frequency conversion. FIG. 4 is a block diagram showing a configuration of a radar transmission apparatus to which the transmission signal generator according to the embodiment is applied.

  The radar transmitter 40 includes an intermediate frequency signal (IF signal) generator 10a as the transmission signal generator 10 shown in FIG. 1, a local signal generator 31 that generates a local signal, a frequency converter 33, and a high frequency signal. And a transmitter 35. The frequency converter 33 frequency-converts (up-converts) the output signal of the IF signal generator 10a to a frequency signal higher than the frequency of the output signal by a local signal, and the high-frequency signal transmitter 35 uses the frequency converter 33 to change the frequency. The converted frequency signal is transmitted.

  By applying the transmission signal generator 10a according to the above embodiment, the radar transmitter 40 sets all the frequencies outside the center signal to zero except for the center frequency of the input signal and a part of the frequency in the vicinity thereof, Since a transmission signal in which the amplitude of the input signal is modulated based on a window function that maximizes the output SNR with respect to the center frequency is generated, spurious components can be suppressed and the signal level of the center frequency can be maximized. Such a radar transmitter can be applied to a transmitter of a radar system.

Industrial application fields

  The present invention can be used for a transmission signal generator that generates a transmission signal in a transmission device of a radar system.

It is a block diagram which shows the outline | summary of the radar apparatus with which the transmission signal generator which concerns on embodiment of this invention is applied. It is a block diagram which shows the structure of the transmission signal generator which concerns on the said embodiment. It is a figure for demonstrating the number of effective data in the transmission signal generator which concerns on the said embodiment. It is a block diagram which shows the structure of the radar transmitter which has the transmission signal generator which concerns on the said embodiment.

Explanation of symbols

10 Transmission Signal Generator 31 Window Function Calculation Unit 32 Transmission Signal Generation Unit

Claims (8)

Except for the center frequency of the input signal and a part of the frequency in the vicinity thereof, all the frequencies outside the input signal are set to zero, and a window function calculation unit that generates a window function that maximizes the output S / N ratio with respect to the center frequency When,
A transmission signal generator that generates a transmission signal obtained by modulating the amplitude of the input signal based on the window function generated by the window function calculator;
A transmission signal generator comprising:   2. The transmission signal generator according to claim 1, wherein the input signal is an unmodulated pulse signal having the same frequency as the center frequency.   3. The transmission signal generator according to claim 2, wherein the transmission signal generation unit generates a plurality of pulse trains obtained by applying phase modulation for each pulse to the amplitude-modulated pulse signal as the transmission signal. .   The transmission signal generator according to claim 1, wherein the input signal is a frequency-modulated pulse signal including the center frequency.   5. The transmission signal generator according to claim 4, wherein the frequency modulation is modulation with a chirp signal.   The window function calculation unit performs the calculation of the window function by multiplying at least once a transformation matrix in which all the row or column elements forming the spurious frequency components to be zero output in the frequency space are zero. The transmission signal generator according to any one of claims 1 to 5, wherein the transmission signal generator is provided.   The transmission signal generator according to claim 6, wherein the transformation matrix is an FFT matrix. Transmission signal generator according to claim 1 to 7,
A frequency converter that converts the output signal of the transmission signal generator to a frequency signal higher than the frequency of the output signal by a local signal;
A signal transmission unit for transmitting a high-frequency signal frequency-converted by the frequency conversion unit;
A radar transmitter characterized by comprising:

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