JP7134886B2 - Surface wave radar device - Google Patents

Description

An embodiment of the present invention relates to a surface wave radar device.

A surface wave radar device is used, for example, to monitor marine vessels, and is used by being installed along the coast of a target sea area. Due to its nature, it mainly transmits and receives in the short wave band, so the size of the antenna tends to be large. Existing devices use Yagi antennas based on the principle of half-wave antennas.

Takashi Yoshida "Revised Radar Technology" The Institute of Electronics, Information and Communication Engineers, October 1, 1996 (first edition)

As described above, the conventional surface wave radar device using the short wave band has a large antenna, and must be fixedly installed at the site for use. In order to increase the angular resolution, a large site area is required to secure the antenna aperture, which is also a major constraint. Furthermore, since the frequency band used is relatively congested, the operating frequency is fixed, and there is a risk of interference with other radar waves and communication waves. There is a demand for a surface wave radar apparatus that solves these problems and has greater mobility.
Accordingly, it is an object of the present invention to provide a movable surface wave radar device.

According to an embodiment, a surface wave radar apparatus includes a transmitting antenna for transmitting radar waves, a receiving antenna section including a plurality of active antennas arranged in an array, and a signal processing section. Each active antenna includes a cylindrical main body, a capacitor hat provided perpendicular to the longitudinal direction of the main body, and a coil for varying the resonance frequency of the active antenna. The signal processing section includes a signal detection section and an angle measurement processing section. The signal detector calculates arrival wave number information of echoes of radar waves from the antenna outputs of the active antennas. The angle measurement processing unit performs angle measurement processing based on information on the number of incoming waves from each antenna output of the active antennas.

FIG. 1 is a top view showing an example of a surface wave radar device according to an embodiment. FIG. 2 is an external view showing an example of the active reception antennas 11, 12, 13, and 14. As shown in FIG. FIG. 3 is a diagram showing a state in which the receiving active antennas 11, 12, 13, and 14 are covered with the radome 212. As shown in FIG. 4 is a diagram showing an example of the installation ladder shown in FIG. 1. FIG. FIG. 5 is a diagram showing an example of an equivalent circuit of a reception active antenna. FIG. 6 is a diagram illustrating an example implementation of a receive active antenna circuit. FIG. 7 is a diagram showing an example of an FPGA circuit. FIG. 8 is a diagram showing an example of an NCO circuit. FIG. 9 is a diagram showing an example of the synchronization circuit 404. As shown in FIG. FIG. 10 is a diagram showing an example of the transmitting antenna 16 shown in FIG. FIG. 11 is a functional block diagram showing an example of a transmitter; FIG. 12 is a timing chart showing an example of radar operation timing. 13 is a functional block diagram illustrating an example of a signal processing unit according to the embodiment; FIG. FIG. 14 is a diagram for explaining the rectangular array calculation by the virtual array processing unit 1206 and the direction-of-arrival estimation calculation by the adaptive processing unit 1207. FIG. FIG. 15 is a diagram for explaining the rectangular array calculation by the virtual array processing unit 1206 and the direction-of-arrival estimation calculation by the adaptive processing unit 1207. As shown in FIG. FIG. 16 is a diagram for explaining the rectangular array calculation by the virtual array processing unit 1206 and the direction-of-arrival estimation calculation by the adaptive processing unit 1207. FIG.

FIG. 1 is a top view showing an example of a surface wave radar device according to an embodiment. This embodiment shows an example in which a vehicle such as a truck is equipped with a transmitting antenna, a motor generator, and a transmitter, and a receiving antenna is installed on the ground. By making the receiving antenna portable, the radar system can be moved and deployed anywhere. Embodiments disclose techniques that enable this.

FIG. 1 shows an example in which four active reception antennas are lowered and installed in a T-shaped arrangement on an installation ladder. The T-shaped array may be an L-shaped array, and the number of arrays may be 4, 6, 8, . . . 2N (N is an integer). In the embodiment, target detection and range finding are based on a DBF (Digital Beam Forming) method, and angle measurement is based on a combination of direction-of-arrival estimation methods.

In FIG. 1, first, the installation ladder 15 is assembled on the ground and fixed with metal stakes 102 that also serve as ground rods. The receiving active antennas 11, 12, 13 and 14 are placed thereon and fixed to the table 103 of the installation ladder with metal screws.

Truck 19 carries transmitting antenna 16 , motor generator 17 and signal processing shelter 18 . A transmitter, a signal processing section, a display section, and the like are mounted on the signal processing shelter 18 . Coaxial cables are connected from the transmitter to the receiving active antennas 11, 12, 13, and 14 to transmit reference signals and the like. Digital reception signals output from the reception active antennas 11, 12, 13, and 14 are also connected to the signal processing unit via an optical cable or the like. Coaxial and optical cables may be integrated into the multi-cable MC.

The installation ladder 15 controls the actuator 101 so that the distance between the receiving active antennas 11, 12, 13, 14 is approximately 0.4λ according to the selected carrier frequency, and the four receiving active antennas 11, 12, 13 and 14 are moved. Similarly, depending on the carrier frequency selected, the transmit antenna 16 is stretched or contracted to 0.5λ (or 0.25λ).

FIG. 2 is an external view showing an example of the active reception antennas 11, 12, 13, and 14. As shown in FIG. In an embodiment, a vertically polarized antenna is adopted as the receiving active antenna. The receiving active antennas 11, 12, 13, and 14 include a cylindrical antenna main body 202, capacitor hats 201, 203, and 211 installed perpendicular to the longitudinal direction of the antenna main body 202, and a coil 204 wound around the antenna main body 202. , 205, 206, 207. Furthermore, by changing the coil length with switches 208, 209, and 210, the antenna resonance frequency can be switched, for example, in four ways. In FIG. 2, the switches 208, 209, and 210 are drawn outside the antenna main body 202 for explanation, but it is convenient to install them inside the cylinder.

The requirements for antenna miniaturization include the following.
a) Increase the diameter of the half-wave antenna so that more surface current can flow.
b) Make an electrical delay.
c) A capacitor hat is provided to lower the resonance frequency.
The configurations shown in FIGS. 2 and 3 can meet such requirements. Increasing the thickness (cylindrical diameter) of the antenna main body 202 is particularly effective.

Also, in order to switch the frequency, the following configuration is used.
d) Equipped with a switch for switching the coil length.
e) Equipped with a matching circuit and a switch for the carrier frequency.
The capacitance of the receiving active antenna is shown in equation (1), the reactance in equation (2), and the coil inductance in equation (3).

Here, H is the antenna height (feet), D is the diameter (inches), and _f0 is the resonant frequency.
That is, the capacity of the receiving active antenna is determined from the diameter D and height H of the antenna main body 202 and the capacitor hat. Therefore, by varying the coil length, it is possible to vary the coil inductance and thereby vary the resonance frequency. 2 and 3 show, as an example, that four types of resonance frequencies can be set. Changing the resonance frequency is related to switching the carrier frequency of the radar wave, which will be described later.

As shown in FIG. 3, the antenna body 202, capacitor hats 201, 203, 211, coils 204, 205, 206, 207, and switches 208, 209, 210 may be housed in a radome 212 such as polyvinyl chloride. . As a result, the inside of the radome 212 can be protected from corrosion due to sea breeze. Aluminum can be used as the material of the antenna main body 202, and copper or the like can be used as the material of the coil.

4 is a diagram showing an example of the installation ladder shown in FIG. 1. FIG. A general electric actuator system can be adopted as the installation ladder. In FIG. 4, the installation ladder comprises a base 901, a guide 902, a table 903 and a motor 904, on which one receiving active antenna can be mounted. In addition, by dividing the base into a plurality of pieces and creating a structure that can be connected on site, it can be easily mounted on a vehicle.

FIG. 5 is a diagram showing an example of an equivalent circuit of a reception active antenna. It is assumed that the active receiving antenna comprises an equivalent receiving circuit 31, a switch 37, matching circuits 32 (32-1, 32-2, 32-3, 32-4), a switch 38, and an equivalent shortened antenna 33 connected in series. If the resistance value of the receiving circuit resistor 301 is set at 50Ω (constant), for example, and the resonance frequency is changed by changing the coil length with a switch, the antenna resistance 304 changes. Therefore, each constant of the matching inductance 302 and the matching capacitor 303 is changed for matching. That is, the matching circuits are provided for the number of resonance frequencies, and are switched by the switches 37 and 38 .

FIG. 6 is a diagram illustrating an example implementation of a receive active antenna circuit. In FIG. 6, the inside of the cylindrical antenna main body 202 is hollow. A mylar sheet 42 is stretched inside the cavity for insulation. Further, a matching circuit 401, a receiving circuit 402, a high-speed A/D (analog/digital) conversion circuit 403, a synchronizing circuit 404, and a power supply circuit 405 are mounted on a flexible substrate, rolled up and placed in the antenna main body.

Matching circuit 401 is the circuit shown in FIG. Receiving circuit 402 includes a low noise amplifier and its peripheral circuits. A high-speed A/D conversion circuit 403 is implemented, for example, in an FPGA (Field Programmable Gate Array) and outputs a received digital signal. Synchronization circuit 404 performs timing synchronization with the radar transmitter and interface of received signals.

FIG. 7 is a diagram showing an example of an FPGA circuit. The FPGA receives the timing signal (transmission start trigger) from the synchronization circuit and CLK (clock), and the NCO circuit 51 generates and outputs an FM demodulated signal. Then, the digital received data from the A/D converter and the FM demodulated signal are multiplied by the multiplier 52, the multiplied image is suppressed by the digital filter 53, and the I/Q quadrature detection is performed by the Hilbert filter 54. Received I and Q data are output.

FIG. 8 is a diagram showing an example of an NCO circuit. The NCO circuit has an N-bit full adder 61 , a latch 62 and a waveform memory 63 . When the phase increment .DELTA..theta. is input to the N-bit full adder 61, a read address according to the phase increment is given to the waveform memory 63, and the frequency waveform is output. As a result, a waveform conforming to FM modulation is output as a digital signal. Δθ is shown in equation (4).

Here, _fOUT is the output frequency, fCLK is the _CLK frequency, and n is the address length of the waveform memory. Equation (5) shows the relationship between n and frequency resolution Δf.

FIG. 9 is a diagram showing an example of the synchronization circuit 404. As shown in FIG. The synchronization circuit 404 includes a bias T 71, a PLL (Phase Lock Loop) circuit 72, and level converters 73 and 74, and applies a bias only at the start of transmission (starting FM modulation) from the radar transmitter to, for example, a 10 MHz CW (continuous wave). A signal added with (DC component) is input as a reference signal. In synchronization circuit 404, a bias T separates the reference signal into an AC signal (10 MHz) and a DC signal (start of transmission). Next, a timing signal is generated from the DC signal, and CLK is generated from the AC signal (10 MHz) using the PLL circuit 72 . The timing signal is taken out as a transmission start trigger through level converter 74 . The CLK signal from PLL circuit 72 is also taken out via level converter 73 .

FIG. 10 is a diagram showing an example of the transmitting antenna 16 shown in FIG. The transmitting antenna 16 has a fishing rod-like (telescopic) structure, and can be extended and retracted according to the carrier frequency of the radar signal by an extension mechanism using a wire or the like. FIG. 10 shows transmission antennas capable of supporting four types of carrier frequencies. As a half wavelength or a quarter wavelength, the case with the longest wavelength corresponds to 81, the second longest case corresponds to 82, the third longest case corresponds to 83, and the shortest wavelength corresponds to 84, respectively.

FIG. 11 is a functional block diagram showing an example of a transmitter; The transmitter includes a reference signal generation circuit 1001, a PLL circuit 1002, a counter circuit 1003, an NCO circuit 1004, a D/A conversion circuit 1005, a transmission ON/OFF switch 1006, an amplifier 1007, a transmission frequency control circuit 1008, and a bias T. A circuit 1009 is provided.

In FIG. 11, a reference signal generation circuit 1001 outputs a reference signal (for example, 10 MHz CW). This reference signal is input to the PLL circuit 1002 and the bias T circuit. PLL circuit 1002 generates a synchronization signal from the reference signal and inputs it to counter circuit 1003 . A counter circuit 1003 generates a timing signal from the synchronization signal and outputs CLK, a transmission ON/OFF signal, and various triggers.

The transmission frequency control circuit 1008 acquires transmission frequency information from the signal processing unit of the signal processing shelter 17 (FIG. 1), and from various triggers from the counter circuit 1003, the transmission antenna 16 and the reception active antenna are controlled at the timing of varying the carrier frequency. Switches 11, 12, 13, and 14 are controlled.

NCO circuit 1004 receives transmission frequency information, a transmission trigger, and CLK, and outputs a digital transmission signal. The D/A conversion circuit 1005 converts the digital signal from the NCO circuit 1004 into an analog signal, amplifies it to the required power in the amplifier 1007 , and feeds it to the transmission antenna 16 . NCO circuit 1004 has the same configuration as shown in FIG. A bias T circuit 1009 superimposes the reference signal from the reference signal generation circuit 1001 and the transmission trigger, and outputs a bias 10 MHz signal.

FIG. 12 is a timing chart showing an example of radar operation timing. The radar period includes a monitor period, a carrier frequency variable period, and a transmission/reception period.
The monitoring period is the time for extracting interference waves in the reception band of the selected carrier frequency.
The carrier frequency variable period is a period during which the frequencies of the transmitting antenna/active receiving antenna are switched and the arrangement of the active receiving antennas 11, 12, 13, and 14 is varied.

The transmission/reception period is a period during which radar waves are transmitted, echoes are received, targets are detected, distances are measured, and angles are measured.
Note that the band selection period may be set immediately after the monitor period.

Counter circuit 1003 of FIG. 11 outputs the radar operation trigger, carrier frequency change trigger, and sector trigger shown in FIG. A radar operation trigger is a trigger for recognizing a monitor period. A sector trigger is a trigger for recognizing the transmission/reception period. A carrier frequency change trigger is a trigger for recognizing carrier frequency variable time.

FIG. 13 is a functional block diagram showing an example of the signal processing section of the signal processing shelter 17 (FIG. 1). Antenna outputs (received signals) from active reception antennas 11 to 14 (N=4) are input to DBF processing section 1201 and FFT processing section 1204 .
The DBF processing unit 1201 performs beam formation by the DBF method. That is, DBF processing section 1201 forms a plurality of reception beams by digital calculation based on the antenna output of each reception active antenna.

Each beam data (beam 1 to beam M) formed simultaneously is input to an FFT (Fast Fourier Transform) processing unit 1202, converted into beat frequencies and Doppler frequencies, and input to a cell extraction processing unit 1203. be. A cell extraction processing unit 1203 performs target detection and distance measurement from each two-dimensional data (beam 1 to beam M). As a result, the cell extraction processing unit 1203 outputs the distance measurement information and the target number information, and the display unit 1208 displays the target distance based on the distance measurement information. The target number information is passed to the adaptive processing unit 1207 .

On the other hand, FFT processing section 1204 generates two-dimensional data (antenna 1 to antenna N) for each antenna from each antenna output of the receiving active antenna by FFT processing, and temporarily stores it in data storage processing section 1205. . Furthermore, based on the detection information from the cell extraction processing unit 1203 , the cell extraction peripheral data is resampled, and the extraction data (antenna 1 to antenna N) are input to the virtual array processing unit 1206 .

The virtual array processing unit 1206 forms a virtual array by rectangular array calculation, and virtually enlarges the antenna aperture formed by the physical arrays (receiving active antennas 11, 12, 13, 14). The adaptive processing unit 1207 performs angle measurement processing based on the rectangular array arithmetic processing data from the virtual array processing unit 1206 and the distance measurement information from the cell extraction processing unit 1203 to obtain target angle measurement information. Angle measurement information is passed to the display unit 1208 and displayed as target information. Of course, tracking processing can also be performed using distance measurement information and angle measurement information.

The output y of the DBF processing section 1201, the phase shift weight W, and the received signal x have the relationship of the following equation (6).

For example, if the number of beams to be formed simultaneously is three, three sets of W phase shift data are prepared, and the results obtained by multiplying the received data for each element by each phase shift weight are added together, so that the output y is three beams. becomes.

As shown in FIG. 13, the output signals from the receiving active antennas 11, 12, 13, and 14 are FM-modulated and converted into beat frequencies, and the FFT processing section 1202 performs FFT processing for each sweep to generate pulses. Compress. Furthermore, the second FFT is performed on the result of N times of FFT processing for each sweep. The first FFT is called the Range FFT and the second FFT is called the Doppler FFT.

Next, the cell extraction processing unit 1203 performs two-dimensional CFAR (Constant False Alarm Probability) processing on the two-dimensional FFT result. CFAR is a process that statistically obtains a threshold from sample data and regards a signal having an amplitude greater than the threshold as a signal. In general, there are cell average, Weibull, OS, etc., and they are selected according to design conditions from external noise distribution, clutter distribution, and the like.

Ranging calculation is performed based on the expression (7) for the signal detected by CFAR. In equation (7), R is the distance, f _Beat is the beat frequency obtained by the first FFT, v is the velocity obtained by the second FFT, c is the speed of light, B is the chirp band, T is the sweep period, and λ is is the wavelength.

14, 15, and 16 are diagrams for explaining the rectangular array calculation by the virtual array processing unit 1206 and the direction-of-arrival estimation calculation by the adaptive processing unit 1207. FIG. For the sake of simplicity, a three-element linear array arrangement is assumed, and a T-shaped arrangement with one additional element will be described. It corresponds to the arrangement of the receiving active antennas shown in FIG. Note that the element spacing is assumed to be 0.4λ in order to suppress the generation of images.

A virtual rectangular array calculation is performed from the T-shaped array shown in FIG. 14 to perform arrival direction estimation processing. Assuming that the active receiving antenna is a T-arrangement array, the data string of the received digital signal is x1, the number of samples is K, and the sampling time is T, equations (8) and (9) hold.

where X _1n is the observed data of the nth element.
Next, observation data obtained by translating the T-shaped array of FIG. 14 by the element spacing (for example, toward the front of the drawing) are expressed by equations (10) and (11). FIG. 15 shows a virtual array rectangular array formed by translation of the T array.

Since the linear array section has different position vectors before and after translation, there is a phase shift, but there is no phase change between x14 (1, 4) and x22 (2, 2). By combining x1 and x2 so as to eliminate the phase difference using this unchanged component, 2×N virtual rectangular array data can be obtained (virtual array forming operation).

Equation (12) is obtained by calculating the correlation C(q) (q=1, 2, . . . , Kq) from the data strings of Xt14 and Xt22.

Here, q is the number of correlation calculation data and * is the complex conjugate. Assuming that the maximum correlation q is q′12 and the number of snapshots is NS, data X′1, X′2 and X′3 used for direction-of-arrival estimation can be obtained as shown in (13) to (15). can be done. Finally, (16) becomes the virtual rectangular array data.

Direction-of-arrival estimation is performed on the data of equation (16) by combining the detection result of the DBF method and, for example, the ESPLIT algorithm. The ESPLIT algorithm is as follows.

First, a correlation matrix is obtained as shown in equations (17) and (18).

where A is the steering vector and F is the amplitude vector.

If we take it as an eigenproblem for the correlation matrix Rxx, we get (19).

The K eigenvalues obtained by solving this are arranged in descending order.

On the other hand, since the number of arriving waves L is determined by the signal detection processing by the DBF method described in FIG. 13, L eigenvalues are selected from the K eigenvalues in descending order. The eigenvectors of the signal subspace are given by equation (20).

Matrix (21) is obtained from matrix (20).

Solving equation (22) for ψ yields equation (23).

Perform an eigenvalue expansion of the matrix (23) and construct the matrix (24) from the eigenvectors belonging to the L eigenvalues equal to zero.

The upper half of the matrix (24) is extracted as the L-order square matrix (25) and the lower half as the L-order square matrix (26), and (27) is calculated.

It is possible to perform eigenvalue expansion of the matrix Ψ and substitute the eigenvalue ψ (l = 1, 2, ..., L) into equation (28) to obtain the arrival angle θl (l = 1, 2, ..., L). can.

As described above, according to the embodiments, it is possible to reduce the size and size of the receiving antenna and to switch frequencies. Activating the receiving antenna eliminates cable loss and compensates for the reduced antenna gain due to shortening. Furthermore, antenna elements can be reduced by high-resolution angle measurement using a virtual rectangular array. That is, the surface wave radar device of the embodiment has the following technical features (1) and (10).

(1) The surface wave radar device has one transmitting antenna 16 and a plurality of receiving active antennas 11, 12, 13, and 14.
(2) The receiving active antennas 11, 12, 13, and 14 are three-dimensional shortened antennas, and a plurality of antennas can be loaded and unloaded on a truck or the like. In addition, a narrow band antenna is used, the receiving frequency can be switched by switch control, and an active antenna having a receiving circuit in the housing is used.
(3) Transmitting antenna 16 is an extendable half-wave or quarter-wave antenna which is loaded on a truck or the like together with a motor generator, transceiver, signal processor and the like.
(4) A plurality of installation ladders are combined, and the receiving active antennas 11, 12, 13, and 14 are fixed to the table of the installation ladder.
(5) The arrangement intervals of the receiving active antennas 11, 12, 13, and 14 fixed to the table of the installation ladder can be changed by the actuator 101 of the installation ladder.
(6) The surface wave radar apparatus varies the antenna length of the transmitting antenna 16 and changes the resonance frequencies of the receiving active antennas 11, 12, 13 and 14 by switch control according to the carrier frequency in the initial setting. Change the antenna arrangement interval of the installation ladder according to the change of the carrier frequency.
(7) First, the surface wave radar device performs only reception, and performs interference wave measurement and noise measurement.
(8) Next, the surface wave radar device performs FMCW (or FMICW) transmission and reception on a carrier frequency that avoids interference waves.
(9) The surface wave radar device performs detection by the DBF method.
(10) The surface wave radar device performs angle measurement by estimating the direction of arrival. However, in order to reduce the number of arrays, after calculation of a virtual rectangular array of receiving antennas in a T-shaped or L-shaped array, angular high resolution is performed by adaptive antenna processing such as MUSIC or ESPLIT.

With the above configuration, it is possible to realize a portable (movable) short wave surface wave radar device, which can monitor ships moving on the sea, for example. In addition, by using the DBF method for detection, direction-of-arrival estimation for angle measurement, and using both adaptive antenna processing and a virtual array for direction-of-arrival estimation, it is possible to reduce the number of arrayed antennas while maintaining angular resolution. Furthermore, by switching the carrier frequency, the Doppler frequency of Bragg resonance scattering from the sea surface is shifted, and targets hidden in clutter can be detected by separating targets from ocean current clutter and ionospheric clutter. These facts make it possible to provide a movable surface wave radar device.

While embodiments of the invention have been described, the embodiments are provided by way of example and are not intended to limit the scope of the invention. This novel embodiment can be embodied in various other forms, and various omissions, replacements, and modifications can be made without departing from the scope of the invention. This embodiment and its modifications are included in the scope and gist of the invention, and are included in the scope of the invention described in the claims and its equivalents.

11 to 14 Reception active antenna 15 Installation ladder 16 Transmission antenna 17 Motor generator 18 Signal processing shelter 19 Truck 31 Equivalent receiving circuit 32 Matching circuit 33 Equivalent shortened antenna , 37, 38 Switches 42 Mylar sheet 51 NCO circuit 52 Multiplier 53 Digital filter 54 Hilbert filter 61 N-bit full adder 62 Latch 63 Waveform memory 71 Bias T 72 PLL circuit 73,74 Level converter 101 Actuator 102 Metal pile 103 Table 201 Capacitor hat 202 Antenna body 203 Capacitor hat 204 to 207 Coil 208 to 210 Switch 211 Capacitor hat 212 Radome 301 Receiving circuit resistance 302 Matching inductance 303 Matching capacitor 304 Antenna resistance 401 Matching circuit 402 Receiving circuit 403 High-speed A /D conversion circuit 404 Synchronization circuit 405 Power supply circuit 901 Base 902 Guide 903 Table 904 Motor 1001 Reference signal generation circuit 1002 PLL circuit 1003 Counter circuit 1004 NCO circuit 1005 D/A conversion circuit 1006 Transmission ON/OFF switch 1007 Amplifier 1008 Transmission frequency control circuit 1009 Bias T circuit 1201 DBF processing unit 1202 FFT processing unit 1203 Cell extraction processing unit 1204 FFT processing unit 1205 data storage processing unit 1206 virtual array processing unit 1207 adaptive processing unit 1208 display unit.

Claims (8)

a transmitting antenna for transmitting radar waves;
a receiving antenna unit comprising a plurality of active antennas arranged in an array;
and a signal processing unit,
each of the active antennas comprising:
a cylindrical body;
a capacitor hat provided orthogonal to the longitudinal direction of the main body;
A coil that varies the resonance frequency of the active antenna,
The signal processing unit is
a signal detection unit that calculates arrival wave number information of echoes of the radar waves from the antenna output of each of the active antennas;
A surface wave radar apparatus comprising: an angle measurement processing unit that performs angle measurement processing based on the arrival wave number information from each antenna output of the active antenna. The signal processing unit further comprises a beam forming unit that forms a plurality of reception beams by digital calculation based on the antenna output of each of the active antennas,
2. The surface wave radar device according to claim 1, wherein said signal detector calculates said arrival wave number information based on said plurality of reception beams. The signal processing unit further includes a virtual array processing unit that expands the aperture of the receiving antenna unit by virtual array arithmetic processing,
2. The surface wave radar device according to claim 1, wherein said angle measurement processing unit calculates target angle measurement information from each of the antenna outputs based on said enlarged aperture. 2. The surface wave radar device according to claim 1, further comprising switching means for switching a carrier frequency of said radar wave. 5. The surface wave radar device according to claim 4, further comprising an actuator for physically varying the arrangement interval of said plurality of active antennas according to said carrier frequency. 5. The surface wave radar device according to claim 4, wherein each of said active antennas has a selector switch for varying the coil length of said coil according to said carrier frequency. 2. The surface wave radar apparatus of claim 1, wherein each of said active antennas comprises a radome housing said body, said capacitor hat, and said coil. 2. The surface wave radar apparatus according to claim 1, wherein each of said active antennas is arranged inside said cylindrical body and comprises a receiving circuit for capturing said echo and outputting said antenna output.

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