JP2017146156A - Radar device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a data rate, speed up initial detection, and reduce a tracking lost.SOLUTION: A radar device according to an embodiment of the present invention comprises an array antenna separated between a transmission system and a reception system. The transmission system divides a transmission pulse into N sub-pulses in a direction of at least one of a time axis and an amplitude axis, changes the modulation signal of each of the N sub-pulses, modulates transmission pulses of the same time by a modulation signal of an addition signal, and transmits from an array antenna of the transmission system. The reception system, after receiving M simultaneous multibeams by the array antenna of the reception system, demodulates them using a signal that corresponds to the modulation signal and acquires N outputs. The array antenna of the transmission system is provided with a plurality of sub-arrays composed of one or more elements, each of the plurality of sub-arrays being provided with a phase shifter for setting a phase that corresponds to beam scanning as necessary, and modulating the sub-pulses by a modulation signal for transmission and sending them out.SELECTED DRAWING: Figure 1

Description

  The present embodiment relates to a radar apparatus that uses multiple beams for transmission and reception.

  In the conventional radar apparatus, the transmission beam and the reception beam are respectively converted into pencil beams by the DBF in the antenna apparatus. In the search, the observation space is sequentially scanned, and in the tracking, the pencil beams are sequentially assigned to a plurality of targets.

DBF (Digital Beam Forming), Yoshida, "Revised Radar Technology", IEICE, pp.289-291 (1996) CFAR processing, Yoshida, 'Revised radar technology', IEICE, pp.87-89 (1996) Ouchi, “Basics of Synthetic Aperture Radar for Remote Sensing”, Tokyo Denki University Press, pp.131-149 (2003) Taylor distribution, Yoshida, 'Revised radar technology', IEICE, pp.134-135 (1996) Angle measurement system (monopulse), Yoshida, 'Revised radar technology', IEICE, pp. 260-264 (1996) Modified cosecant square beam, Yoshida, 'Revised radar technology', IEICE, pp.110-111 (1996) Pattern shaping by phase, Robert C. Voges, ‘Phase Optimization of Antenna Array Gain with Constrained Amplitude Excitation’, IEEE Trans. Antennas & Propagation, AP-20, No.4, pp.432-436 (1972)

  As described above, in the conventional radar apparatus, the transmission beam and the reception beam are each made into a pencil beam by the DBF in the antenna apparatus, and the target is searched and tracked in a time division manner, and there is a time constraint per position. There was a problem that the number of hits was small, the SN was low, the data rate was slow, the initial detection was delayed, and the tracking was lost.

  The present embodiment has been made in view of the above problems, and an object thereof is to provide a radar apparatus that can improve the data rate, speed up the initial detection, and reduce the tracking loss.

  According to the embodiment, the radar apparatus includes an array antenna in which a transmission system and a reception system are separated. The transmission system divides a transmission pulse into N (N ≧ 2) subpulses with respect to at least one of a time axis and an amplitude axis direction, and changes a modulation signal of each of the N subpulses. The transmission pulse of the same time is modulated by the modulation signal of the addition signal and transmitted by the array antenna of the transmission system. The reception system receives M (M ≧ 1) simultaneous multi-beams by the array antenna of the reception system, and then demodulates using a signal corresponding to the modulation signal to obtain N outputs. The array antenna of the transmission system includes a plurality of subarrays composed of one or more elements, and each of the plurality of subarrays includes a phase shifter for setting a phase corresponding to beam scanning as necessary. The sub-pulse is modulated by a modulation signal for transmission and transmitted.

The block diagram which shows the structure of the whole system | strain of the radar apparatus which concerns on 1st Embodiment. The block diagram which shows the structure of each system | strain of the transmission subarray of the radar apparatus shown in FIG. 1, and a reception subarray. The block diagram which shows the other structure of the transmission system shown in FIG. FIG. 4 is a block diagram showing a configuration of a transmission modulator (first embodiment) shown in FIG. 3. The conceptual diagram which shows a mode that a transmission fan is formed with a multi-beam with the transmission system | strain shown in FIG. The conceptual diagram which shows a mode that a transmission pencil beam is formed with a multi-beam by the transmission system shown in FIG. The conceptual diagram which shows the example of a division | segmentation of a transmission pulse in the transmission system shown in FIG. The conceptual diagram which shows the coordinate system of the position vector of an antenna element, and an observation vector in the transmission system shown in FIG. The figure which shows the example of a division | segmentation of observation space and a transmission pulse in the transmission system shown in FIG. The figure which shows the example of a division | segmentation of the transmission pulse when observation space is expanded in the transmission system shown in FIG. The block diagram which shows the structure of the 2nd Example of the transmission modulator used for the transmission system | strain shown in FIG. 3 as 2nd Embodiment. FIG. 12 is a waveform diagram showing a transmission signal generation process when the modulation transmitter according to the second example shown in FIG. 11 is used in the second embodiment. The figure which shows the example of a division | segmentation of observation space and a transmission pulse in 2nd Embodiment. The block diagram which shows the specific structure of the signal processor of the receiving system shown in FIG. 1 as 3rd Embodiment. 9 is a flowchart showing a processing flow of a radar apparatus according to a third embodiment. The wave form diagram which shows the monopulse pattern and target range-error voltage characteristic of a receiving beam in 3rd Embodiment. In 3rd Embodiment, the wave form diagram which shows the other monopulse pattern and target range-error voltage characteristic of a receiving beam. The block diagram which shows the DBF structure of the two-dimensional virtual array of the radar apparatus which concerns on 4th Embodiment. The conceptual diagram which shows the mode of the two-dimensional virtual array formation of the radar apparatus which concerns on 4th Embodiment. The conceptual diagram which shows the coordinate system of the position vector of an antenna element, and an observation vector in the receiving system of the radar apparatus which concerns on 4th Embodiment. The conceptual diagram which shows the arrangement configuration of the transmission array of the radar apparatus which concerns on 4th Embodiment, and a receiving array. The conceptual diagram which shows the deformation | transformation second beam of the radar apparatus which concerns on 5th Embodiment. The conceptual diagram which shows the example of a division | segmentation of the observation space and transmission pulse of the radar apparatus which concerns on 5th Embodiment. The conceptual diagram which shows the example of beam grouping of the radar apparatus which concerns on 5th Embodiment. The conceptual diagram which shows the example of a division | segmentation of the observation space and transmission pulse of the radar apparatus which concerns on 5th Embodiment.

  Hereinafter, embodiments will be described with reference to the drawings. In the description of each embodiment, the same portions are denoted by the same reference numerals, and redundant description is omitted. In the following description, it is assumed that the embodiment of the antenna device is applied to a radar device.

(First embodiment) (Transmission sub-pulse division)
The first embodiment will be described with reference to FIGS. 1 to 10.

  FIG. 1 is a block diagram showing the configuration of each system of the entire transmission and reception of the radar apparatus according to the first embodiment, and FIG. 2 is a block diagram showing the configuration of each system of the transmission subarray and the reception subarray shown in FIG. 3 is a block diagram showing another configuration of the transmission system of the radar apparatus shown in FIG. 1, and FIG. 4 is a block diagram showing a specific configuration of the transmission modulator (referred to as the first embodiment) shown in FIG. is there.

  FIG. 1A shows the entire transmission system. In the transmission system shown in FIG. 1A, a radar transmission signal is sent to the Mt transmission distributor 11. The Mt transmission distributor 11 distributes an input transmission signal to Mt systems, and the transmission signals distributed to each system are supplied to Nt transmission distributors 121 to 12Mt, respectively. Each of the Nt transmission distributors 121 to 12Mt distributes the input transmission signal to the Nt system, and the transmission signal distributed to each system is supplied to the transmission subarrays 1311 to 13NtMt, respectively. Each of the transmission subarrays 1311 to 13NtMt is inputted with a beam scanning angle together with a radar transmission signal.

  The radar transmission signal and the beam scanning angle signal supplied to the transmission subarray 13 nm (n = 1 to Nt, m = 1 to Mt) are modulated by the transmission modulator 14 as shown in FIG. After being applied, it is supplied to the St transmission distributor 15 as a subarray transmission signal. This St transmission distributor 15 distributes the input transmission signal to the St system, and the transmission signals distributed to each system are given a phase shift amount corresponding to the beam scanning by the transmission phase shifters 161 to 16St, respectively. After that, the power is amplified by the transmission amplifiers 171 to 17St, and is transmitted to the space from the antenna elements 181 to 18St.

  In the transmission system configuration, transmission modulation processing is performed in units of subarrays. However, as shown in FIG. 3, a transmission modulator 14 nm is provided in each system of all antenna elements 18 nm, and transmission is performed in units of element systems. You may make it perform a modulation process. In this case, since phase modulation is possible in each system, a phase shifter for each system becomes unnecessary. FIG. 4 shows a specific configuration of the transmission modulator 14 nm. 4 includes a modulation unit 141 and a phase calculation unit 142. The phase calculation unit 142 calculates a phase amount corresponding to the beam scanning angle, and the modulation unit 141 calculates the phase amount calculated from the transmission signal. Multiply and apply modulation.

  FIG. 1B shows the entire receiving system. The reception system shown in FIG. 1B includes Nr reception subarrays 211 to 21Nr. As shown in FIG. 2B, the reception sub-arrays 211 to 21Nr of each system capture incoming radio waves by the antenna elements 241 to 24Sr of the Sr system. The captured signals are amplified with low noise by amplifiers 251 to 25Sr, respectively, converted to an intermediate frequency by a frequency converter 26, converted to a digital signal by an AD converter 27, and received signals # 1 to ## of the Sr system. Sr, and the sub-array beam combiner 28 combines the sub-array multi-beam outputs # 1 to #Bn of the Bn system. The multi-beam outputs obtained by the subarrays 211 to 21Nr are combined into a prescribed number of beams by the beam combiner 22 and sent to the signal processor 23 as shown in FIG. As will be described in detail later, the signal processor 23 detects a target signal from the multi-beam output obtained by each of the subarrays 211 to 21Nr, performs distance measurement and angle measurement processing on the detected target, and generates a radar output.

  In the above configuration, the radar apparatus of this embodiment will be described below.

  In the conventional radar apparatus, in order to improve the system gain, the transmission pencil beam is directed toward the observation range, and the reception pencil beam is directed in that direction. In order to expand the observation range, the transmission pencil beam is sequentially scanned so as to cover the observation range, and the reception pencil beam is also scanned accordingly. For this reason, observation time will become long according to expansion of an observation range. On the other hand, since the transmission pencil beam is directed in the target direction, there is a problem that radar transmission is easily detected from the target. In addition, depending on the transmission direction, there is a possibility that the existing radio equipment may be affected by radio wave interference. The radar apparatus according to this embodiment solves these problems.

  First, an example of a beam forming technique for transmission and reception in the present embodiment will be described with reference to FIGS. FIG. 5 shows a technique for improving the data rate by forming a fan beam as a transmission beam and forming a reception multi-beam within the range, and is mainly used in a search mode. On the other hand, FIG. 6 shows a mode in which a large number of targets scattered in the observation space are tracked and observed, and is an example in which both the transmission beam and the reception beam are pencil beams.

  In these cases, the reception array may be an analog beam or DBF (Digital Beam Forming, see Non-Patent Document 1) as long as simultaneous multi-beams can be formed. On the other hand, in the transmission array, the output of the transmission module is limited, and in order to form a simultaneous multi-beam, the pulse shown in FIG. 7A is divided into sub-pulses in at least one axis direction in the time axis or amplitude axis direction. FIG. 7B shows a case of dividing along both axes, FIG. 7C shows a case of dividing along the time axis, and FIG. 7D shows a case of dividing along the amplitude axis. There are various other methods such as changing the arrangement order.

  As described above, at the time of transmission, a transmission multi-beam can be formed by setting the phase for controlling the transmission beam direction to the corresponding antenna element for each sub-pulse. During reception, multiple beams are simultaneously formed in the direction of the transmission beam within a PRI (Pulse repetition Interval).

  A signal flow will be described with reference to the system diagrams of FIGS. 1 and 2.

  First, in the transmission system of FIG. 1A, an RF (Radio Frequency) band transmission signal is input to the transmission distributor 11 and distributed to the Mt system of the AZ axis (EL axis), and further the transmission distributors 121 to 12Mt. Is distributed to the Nt system of the EL axis (AZ axis) and input to the transmission subarrays 1311 to 13NtMt. In the transmission subarrays 1311 to 13NtMt, as shown in FIG. 2A, a signal obtained by modulating the transmission signal by the transmission modulator 14 is distributed to the St system by the transmission distributor 15, and respectively transmitted by the transmission phase shifters 161 to 16St. After setting the phase shift amount for beam scanning, the output is amplified by the transmission amplifiers 171 to 17St, and transmitted to the space from the antenna elements 181 to 18St.

  In the receiving system of FIG. 1B, the received signals of the incoming radio waves captured from the antenna elements 241 to 24Sr of FIG. 2B are amplified with low noise by the amplifiers 251 to 25Sr, and converted to an intermediate frequency by the frequency converter 26. After that, the AD converter 27 converts it into a digital signal. Using this signal, the subarray beam combiner 28 performs DBF processing and outputs a received multi-beam. In the reception system, the reception subarray signal is synthesized by the beam combiner 6 in FIG. 1B, and the signal of the entire aperture is synthesized. The multi-beam output of the entire aperture is used, and the signal processor 23 performs FFT, pulse compression, Signal processing such as CFAR (see Non-Patent Document 2) is performed. Note that signal processing may be performed for each subarray output.

  Next, before describing the phase setting for directing the transmission beam in an arbitrary direction, methods for realizing the various sub-pulse division schemes in FIG. 7 will be described. When dividing on the time axis, the phase may be set by one phase shifter for each transmission module. On the other hand, when dividing by the amplitude axis, a plurality of phase shifters and high-power amplifiers are required, which becomes difficult to realize when the number of transmission beams increases. As a countermeasure, a signal obtained by changing the modulation signal for the number of subpulses is used. For this purpose, it is necessary to take isolation between subpulses, but a specific method example will be described in the second embodiment. For this modulation signal, the phase for each transmitting element and the phase depending on the beam scanning direction may be set.

When the set phase is formulated, it is expressed as follows with reference to the coordinate system shown in FIG.

FIG. 3 shows an example in which different modulation is possible for each transmitting antenna element. In this case, each transmission modulation signal is isolated and a phase shift amount for beam scanning is set in the transmission modulation signal, thereby eliminating the need for a phase shifter.

This system is shown in FIG. The input is a transmission signal (RF signal, high-frequency signal) and a beam scanning angle. The phase calculation of the phase shift amount of equation (2) depending on the beam scanning angle is performed, and a signal obtained by multiplying each modulation signal is output as a modulation signal. .

When the modulation signal of each antenna element cannot be controlled due to hardware restrictions, the modulation signal is controlled for each subarray, and the transmission system is as shown in FIG. In this case, since the beam scanning is controlled only by the transmission modulation signal in units of subarrays, a grating lobe tends to occur. Therefore, the center direction of the range in which the transmission beam is formed is set by the phase shifter of the subarray, and a modulation signal including a phase for forming the transmission multi-beam in the range is generated. The modulation signal in this case is formulated as follows.

The modulation signal is represented by the following equation including the phase shift amount for beam scanning of the subarray.

Examples of observation space dividing methods are shown in FIGS. In either case, the observation space is divided into an upper part and a lower part, and in FIG. 9, the AZ axis is isolated by frequency using up-chirp and down-chirp among chirp signals. FIG. 9A shows an example of dividing the observation space, and FIGS. 9B and 9C show examples of dividing the transmission pulse. The subscripts u and d represent up chirp and down chirp, respectively. FIG. 9B is arranged on the amplitude axis in order to narrow the transmission pulse width, and isolation is ensured by the frequency and the direction of the chirp. FIG. 9 (c) shows an example of arrangement on the time axis in order to suppress the peak output of the transmission pulse. FIG. 10 shows a case where the frequencies are alternately arranged on the EL plane and the AZ plane as shown in FIG. 10A in order to select the number of frequencies. The subscripts u and d are the same as described above, and the subsequent numerical values (1 to 3) represent the types of phases of the respective antenna elements corresponding to the transmission beam directing direction of AZ or EL.

  In this case, as a method of dividing the sub-pulse, in order to ensure the same time isolation within the transmission pulse, there are a maximum of four ways of two frequencies × two directions of chirp, as shown in FIG. They are arranged in the time axis direction according to the directivity direction of the transmission beam. In short, for the observation space, the isolation is ensured at the position where the transmission pulse is adjacent, and for the sub-pulse division of the transmission pulse, the isolation is ensured in the direction of the amplitude axis at the same time of the transmission pulse. If the number of types of necessary transmission pulses is more than that, they may be arranged in the time axis direction.

  In the present embodiment, a transmission multi-beam is formed by dividing a transmission sub-pulse by an amplitude axis and a time axis and allocating to each observation space, and reception is a method of forming a reception multi-beam corresponding to the transmission multi-beam direction. . This method can also be applied to other sub-pulse division methods in accordance with this gist and observation space division method.

  In addition, a transmission phase shifter and a transmission modulator are used to realize transmission subpulse division, but only one of them may be used as long as isolation between transmission multi-beams can be secured.

  In addition, the beam scanning method by the modulation by the subarray of FIG. 1 has been described. The transmission beam is directed to the center of the range to be scanned by the modulation signal by the subarray, and the transmission pencil having a narrow beam width is transmitted by the transmission phase shifter. Needless to say, a method of determining the beam directing direction may be used. However, in this case, the setting of the transmission phase shifter is time division as shown in FIG.

(Second Embodiment) Frequency Division In the first embodiment, the method of dividing a transmission pulse into sub-pulses to form a transmission multi-beam has been described. In the present embodiment, a method for isolating transmission beams will be described.

  As a method for obtaining isolation, there is a method of changing the center frequency for each sub-pulse. In this case, frequencies corresponding to the number of subpulses are required, and reception also increases the number of local signals and increases the hardware (HW) scale. For this measure, the second embodiment describes a method for frequency-dividing a chirp signal. The entire system is the same as that of the first embodiment, and the transmission modulator 14 therein is different. FIG. 11 shows a system diagram of the transmission modulator (second example).

  In FIG. 11, a reference signal (chirp, encoded code, etc.) using a predetermined whole band is supplied to the transmission modulator 14 as a transmission signal. This reference signal is converted into a frequency axis signal for the range axis by the range axis FFT processing unit 1413, divided into Nch frequency bands by the frequency division unit 1414 using the frequency filter, and the range axis inverse FFT processing unit 1415 for the range axis. The signal is converted into a time-axis signal, and the RF signal modulation unit 1416 modulates the RF (pulse) signal.

  The state of the modulation is shown in FIG. FIG. 12A shows a modulation pulse waveform for a full band chirp as a reference signal. This signal is converted into a frequency axis signal in the chirp band by FFT as shown in FIG. 12 (b), and ΔBn is selected in all frequency bands as shown in FIG. 12 (c). As shown in d), it is distributed to a plurality of channels and converted into any one band to obtain a transmission waveform shown in FIG.

  At this time, the instruction input of the beam scanning angle is converted into a phase shift amount by the phase calculation unit 1417, and a predetermined phase is set in the modulation signal by the modulation unit 1416 based on the phase shift amount. The modulation signal generated in this way is amplified with high output and sent out from the antenna element to the space, as in the first embodiment.

  Note that a predetermined phase may be set by a phase shifter provided in each system, and then amplified with high output by an amplifier and transmitted by an antenna element.

  FIG. 13 shows an example of arrangement of observation space and sub-pulse division of transmission pulses in this embodiment. Assuming that the number of frequency divisions is N, each can secure isolation. Therefore, with respect to the observation space shown in FIG. 13 (a), as shown in FIG. 13 (b) and FIG. Subpulses can be arbitrarily arranged within the constraints of transmission duty (transmission pulse width / pulse repetition period).

(Third Embodiment) Range Axis Monopulse In the second embodiment, since the frequency band is divided into N by the number N of transmitting elements, the range resolution is reduced to 1 / N, and the range accuracy is also reduced accordingly. As a countermeasure, in order to improve the range accuracy, a method using a range axis phase monopulse during pulse compression (see Non-Patent Document 3), a signal processor 23 of the reception system shown in FIG. This will be described with reference to the flow.

  First, the received multi-beam signal acquired by PRF transmission / reception (step S1) is AD converted (step S2), and a signal sig (t) near the target detected cell is extracted.

Next, in the range axis FFT processing unit R1, the input signal sig is subjected to FFT processing for the range axis (step S3).

Next, in the reference signal generation unit R7, a Σ reference signal (in the case of a linear chirp signal) used in a range axis phase monopulse described later is generated (step S4). This reference signal is expressed as follows.

The reference signal for the Δ signal of the range axis phase monopulse is given by the following equation.

The sample lengths of the reference signals SrefΣ (t) and SrefΔ (t) are replaced with signals that are zero-padded according to the input signal.

This is subjected to FFT processing by the reference signal FFT processing unit R8, thereby obtaining a frequency axis signal of the reference signal (step S5).

Thus, the multiplication unit R2 multiplies the frequency domain input signal and the reference signal (step S6). This signal is given by

Next, the weight multiplier R3 calculates a weight for reducing the range side lobe after the pulse compression (step S7). As the weight, a Taylor weight (see Non-Patent Document 4) or the like may be selected according to the setting of the range side lobe.

These are converted into time-axis signals by the inverse FFT processing unit R4 to obtain the following equation (step S8).

It should be noted that the term of the exponential function of SΔ has the same phase shift between Σ and Δ.

Further, the time axis t is converted to the range axis R by the relationship of the following equation.

From the result of Σ in equation (18), a detection cell (time sample) q (q = 1 to Q) whose amplitude exceeds a predetermined threshold is extracted, and in each of the range axis monopulse processing unit R5 and the range calculation unit R6, A distance measurement process by monopulse calculation is performed on the detected cells (step S9), and the distance obtained by this process is output (step S10). The following equation is used for this monopulse calculation.

  For the error voltage and range, as shown in FIG. 16 ((a) is a monopulse pattern, (b) is the error voltage characteristics of the target range), the error voltage for the range is tabulated in advance and an error voltage table is created. Keep it. The range R is calculated using a table from ε calculated by the equation (14). This method can be said to be a method in which the phase monopulse method (see Non-Patent Document 5) as an angle measurement method is replaced with a range axis (time axis).

  In the description of the above embodiment, phase monopulse processing has been described, but other processing such as amplitude monopulse may be applied. FIG. 17 shows an error voltage in the case of amplitude monopulse processing ((a) is a monopulse pattern, and (b) is an error voltage characteristic of a target range).

(Fourth Embodiment) Two-dimensional virtual array DBF
The antenna array has a simple configuration when transmission and reception are separated. As this merit, since transmission and reception are separated, isolation is increased, and reception is possible during transmission, and there is no restriction on the minimum reception distance, and the transmission pulse width can be extended.

  As a configuration for separating transmission and reception, for example, there is a method of dividing into upper and lower (left and right) half openings. In this case, since the aperture is halved for both transmission and reception, when considering transmission output × transmission gain × reception gain (Pt × Gt × Gr), it is reduced by 9 dB (3 + 3 + 3 dB), resulting in a large loss. Based on this countermeasure, an example using a virtual array will be described.

  In the present embodiment, as a configuration example of a transmission / reception separation radar apparatus, a system using reception using different two-axis linear arrays will be described. FIG. 18 shows a system of a radar apparatus using a subarray. FIG. 19 shows an overview of a two-dimensional virtual array.

  In the radar apparatus shown in FIG. 18, for transmission, the transmission apparatus D6 divides the transmission sub-pulses into transmission multi-beams by the same technique as in the first embodiment. As for reception, reception processing is performed by the two-dimensional virtual array shown in FIG. That is, N column reception XA1 to XAN and M column reception XB1 to XBM shown in FIG. 19A are combined, and a virtual array of N × M elements is formed by multiplication of reception element signals as shown in FIG. 19B. To do.

  The operation principle of this two-dimensional virtual array will be described. Here, for easy understanding, consider a case where the subarrays 211 to 21Nr in FIG. 1B are divided into an N channel of the A-axis array D11 and an M channel of the B-axis array D1Rs. The subarray system is the same as that shown in FIG.

After pre-processing each of the signal processors D21 to D1Rs to the subarray beam combined signals of both the A axis and the B axis, the virtual array converter D3 performs a multiplication operation for each subarray signal to obtain N × M Generate a virtual array signal. This is formulated. First, when the biaxial input signals including the observation direction (AZ, EL) are respectively expressed as Xa and Xb, the following equations are obtained. The coordinate system of this embodiment is shown in FIG.

In consideration of the case where the separation distance between the A-axis array and the B-axis array is large, the AZ angle and the EL angle are separated by adding subscripts a and b, but when the separation distance is small, the A The AZ angle and the EL angle as seen from the axis array and the B axis array are equal.

From the above, when the signal input to the phase center of the virtual two-dimensional array is Xin, the two-axis signals Xa and Xb are expressed by the following equations.

When this signal is used to multiply both vectors, which is the main point of the method of this embodiment, the following equation is obtained.

Next, each element becomes the following equation.

Here, considering the case where the separation distance between the A-axis array and the B-axis array is small, and ka = kb, the following equation is obtained.

This indicates that a virtual element signal is generated at the position of addition of the position vectors of the an and bm subarrays by multiplication. In the beam synthesizer D4, the beam combiner D4 multiplies the element of the equation (25) by a sidelobe reduction tailor weight (see Non-Patent Document 4) or the like as a sidelobe reduction weight to control the beam pointing direction. Are multiplied by DBF (Digital Beam Forming, see Non-Patent Document 1), and the following equation is obtained.

The weight Wpnm for controlling the beam direction can be expressed by the following equation.

  In order to form a multi-beam by the signal processor D5 using this virtual array signal X, a plurality of AZp and ELp in the equation (31) may be set. With this virtual array, the receiving aperture area can be fully used as shown in FIG. In this case, although the transmission aperture area is slightly reduced, a higher PtGtGr can be obtained than dividing each half aperture. For example, when the aperture is divided into 16 × 4 × 4, the transmission aperture area is 54% (9/16) and the reception is 46% (7/16), which is about 5 dB (20 log (9/9 / PtGt). 16)) is a decrease, and it can be said that PtGtGr is higher than the aforementioned half-aperture division (−9 dB).

  The transmission sub-pulse division described in the first embodiment forms a transmission multi-beam, and the reception virtual array described in this embodiment forms a multi-beam in the transmission direction, thereby effectively using the antenna aperture area. A radar apparatus capable of observing at a high data rate with multiple beams can be configured.

(Fifth Embodiment) Transmission by Modified Cosecant Square Beam In the fourth embodiment, a technique for generally forming transmission and reception multi-beams has been described. In the fifth embodiment, a technique for efficiently dividing the observation space and reducing the number of sub-pulse divisions will be described.

  FIG. 22 shows the beam forming method of this embodiment. Since the lowermost part is a long distance and the upper part is a relatively short distance, the observation space is divided into a lower part and an upper part, and the upper transmission is a method of covering with a modified cosecant square beam (see Non-Patent Document 6). is there. Thereby, since the number of beam positions can be significantly reduced, the transmission energy (transmission output × pulse width) per sub-pulse can be increased and the system gain can be improved.

  FIG. 23 shows an observation space and transmission pulse examples. In this example, in the observation space, as shown in FIG. 23A, for example, transmission pulses obtained by dividing the frequency into two are assigned to the lower side and the upper side. In the transmission pulse, as shown in FIG. 23B or FIG. 23C, the sub-pulse may be divided in the amplitude axis direction or the time axis direction.

  As another method, a method for efficiently dividing the observation space and reducing the number of sub-pulse divisions as shown in FIG. 24 will be described. When the target direction can be grouped by tracking or the like, the number of transmission beams can be reduced. Thereby, since the number of beam positions can be significantly reduced, the transmission energy (transmission output × pulse width) per sub-pulse can be increased and the system gain can be improved. For the transmission beam, a transmission beam shaping method based on phase control (see Non-Patent Document 7) may be applied so as to cover each grouped observation range.

FIG. 25 shows an observation space and transmission pulse examples. As for the observation space, as shown in FIG. 25 (a), different frequencies are assigned in the direction of forming the transmission beam, and for the transmission pulse, the sub-pulses may be divided as illustrated in FIG. 25 (b). . In order to reduce the frequency, it goes without saying that other arrangements may be selected so as to ensure isolation of the transmission pulse at the same time as the adjacent space.

  In addition, the said embodiment is not limited as it is, In the implementation stage, a component can be deform | transformed and embodied in the range which does not deviate from the summary. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

DESCRIPTION OF SYMBOLS 11 ... Mt transmission distributor, 121-12Mt ... Nt transmission distributor, 1311-13NtMt ... Transmission subarray, 14 ... Transmission modulator, 141 ... Modulation part, 142 ... Phase calculation part, 1413 ... Range axis FFT processing part, 1414 ... Frequency division unit (frequency filter), 1415 ... range axis inverse FFT processing unit, 1416 ... RF signal modulation unit, 1417 ... phase calculation unit, 15 ... St transmission distributor, 161 to 16 St ... transmission phase shifter, 171 to 17 St ... Transmitting amplifier, 181 to 18St ... antenna element,
211 to 21 Nr: reception subarray, 22: beam combiner, 23: signal processor, 241-24Sr: antenna element, 251-25Sr: amplifier, 26: frequency converter, 27: AD converter, 28: subarray beam combiner ,
R1 ... range axis FFT processing unit, R2 point multiplication unit, R3 ... weight multiplication unit, R4 ... inverse FFT processing unit, R5 ... range axis monopulse processing unit, R6 ... range calculation unit, R7 ... reference signal generation unit, R8 ... reference Signal FFT processing unit,
D11 to A axis array, D1Rs to B axis array, D21 to A axis signal processor, D1Rs to B axis signal processor, D3 to virtual array converter, D4 to beam synthesizer, D5 to signal processor .

Claims (6)

Equipped with an array antenna that separates the transmission system and the reception system,
The transmission system divides a transmission pulse into N (N ≧ 2) subpulses with respect to at least one of a time axis and an amplitude axis direction, and changes a modulation signal of each of the N subpulses. The transmission pulse of the same time is modulated by the modulation signal of the addition signal and transmitted by the array antenna of the transmission system,
The receiving system receives M (M ≧ 1) simultaneous multi-beams by the array antenna of the receiving system, and then demodulates using a signal corresponding to the modulated signal to obtain N outputs. ,
The array antenna of the transmission system includes a plurality of subarrays composed of one or more elements, and each of the plurality of subarrays includes a phase shifter for setting a phase corresponding to beam scanning as necessary. A radar apparatus that modulates and transmits the sub-pulse with a modulation signal for transmission.   The radar apparatus according to claim 1, wherein the plurality of subarrays further include a phase of a subarray for beam scanning in the modulation signal for transmission.   The radar apparatus according to claim 1, wherein the transmission system divides at least one chirp frequency of up-chirp or down-chirp as the modulation signal and assigns it to the sub-pulse.   When observing the range of the range axis, the receiving system divides the range axis signal into two parts, the first half and the second half, and uses the Σ signal and Δ signal of both to calculate the range using range axis monopulse processing. The radar apparatus according to claim 1. The array antenna of the receiving system is
A first receiving array for obtaining a signal Xan (n = 1 to N) by N (N ≧ 1) subarrays arranged one-dimensionally along a first axis (A axis);
A second receiving array for obtaining a signal Xbm (m = 1 to M) by M (M ≧ 1) subarrays arranged one-dimensionally along a second axis (B axis) different from the first axis; ,
The virtual array signal of the N × M subarray is obtained by performing multiplication Xan × Xbm (n = 1 to N, m = 1 to M) on the beam output of each subarray of the first axis and the second axis. A signal processor that multiplies each virtual array signal by a weight and adds it to form a multi-beam in a predetermined angular range,
The radar apparatus according to claim 1, wherein the array antenna of the transmission system is disposed in an opening other than the opening of the reception system. In the transmission space, in the observation space, transmission in the EL direction forms a modified cosecant beam and, if necessary, a pencil beam below,
The radar apparatus according to claim 1, wherein the receiving system receives a multi-beam.

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