JPH0248071B2 - REEDAASOCHI - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention uses an electronically scanned monopulse antenna that generates a monopulse pattern in the vertical plane in an electronically scanned array radar that performs beam scanning electronically in the vertical plane. The present invention relates to a radar device that performs off-axis monopulse angle measurement computation compatible with the above, and achieves high-precision height measurement over a wide elevation angle range and the entire radar transmission frequency band.

Typical examples of electronically scanned array radars include phase scanned array radar, frequency scanned array radar, and phase/frequency composite array radar, and the number of simultaneously generated beams in the vertical plane ranges from 1 to 1. Although there are various methods including a plurality of beams, the following explanation will be made using an example in which the number of simultaneously generated beams in the vertical plane is one.

FIG. 1 shows a conventional radar device to which the present invention is applied. In FIG. 1, 1 is an array antenna, which is composed of a first array antenna 1a and a second array antenna 1b. First array antenna 1a
The second array antenna 1b has antenna elements 1a1 to 1am and 1b1 to 1bm, respectively. 2 is a phase shifter, which includes a first phase shifter group 2a and a second phase shifter group 2b.
Consists of. The first and second phase shifter groups 2a, 2b
are phase shifters 2a1-2am, 2b1-2, respectively.
Has bm. 3 is a distribution circuit, the first distribution circuit 3
a and a second distribution circuit 3b. 4 is a hybrid circuit which outputs a sum signal Σ and a difference signal Δ of the inputs from the first and second distribution circuits 3a and 3b. 5 is a phase shifter drive circuit, 6 is a beam control circuit, 7 is a transmitter, 8
9 is a reference signal generation circuit, 9 is a transmitting/receiving switch, 10a,
10b is a high frequency amplifier circuit, 11a and 11b are first
Mixing circuits, 12a and 12b are second mixing circuits, 13
a, 13b are intermediate frequency amplification circuits, 14a, 14b
15 is a moving target detection circuit, 15 is a signal processing circuit, and 16 is a moving target detection circuit.
is a display circuit.

Next, the operation will be explained.

The first intermediate frequency transmission seed signal and the first local oscillation frequency generated by the reference signal generation circuit 8 are frequency-mixed by the transmitter 7 to become a transmission signal, which is divided into two by the hybrid 4 via the transmission/reception switch 9. 1st
The power is fed to the distribution circuit 3a and the second distribution circuit 3b and divided into m, respectively, and given a predetermined phase amount by the first phase shifter group 2a and the second phase shifter group 2b. It is radiated into space from two array antennas 1b.

The phase setting amount of the first phase shifter group 2a and the second phase shifter group 2b is determined by the beam control circuit 6 based on the beam scanning angle command and timing from the reference signal generation circuit 8. 2b and is applied via the phase shifter drive circuit 5.

The transmission signal radiated in a predetermined direction in this way is partially reflected by the target, and is transmitted to the first array antenna 1a and the second array antenna 1.
b, first phase shifter group 2a, second phase shifter group 2b, first
The signals become the first and second inputs of the hybrid 4 via the distribution circuit 3a and the second distribution circuit 3b.

In the hybrid 4, the sum (Σ) and difference (Δ) of these two inputs are output from the two output terminals, and the sum (Σ) output is sent via the transmitter/receiver switch 9 to the sum (Σ)
The difference (Δ) output becomes the signal system receiver input, and the difference (Δ) output becomes the difference (Δ) signal system receiver input.

Since the reception processing is the same for both the sum (Σ) signal system and the difference (Δ) signal system, the sum (Σ) signal system will be representatively explained below.

First, the sum (Σ) output is amplified with low noise in the high frequency amplifier circuit 10a, mixed with the first local oscillation frequency from the reference signal generation circuit 8 in the first mixing circuit 11a, and converted into a first intermediate frequency signal. Similarly, the second mixing circuit 12a receives the second signal from the reference signal generating circuit 8.
The signal is mixed with the local oscillation frequency and converted into a second intermediate frequency signal, which is input to the moving target detection circuit 14a.

The moving target detection circuit 14a generally uses MTI ( M
It is a filter that eliminates unnecessary reflected waves (clutter) from the ground surface, weather , etc. in response to the transmission pulse repetition frequency generated by the reference signal generation circuit 8 . is forming.

The moving target detection circuit 14a can have various circuit configurations depending on the system, but in conventional devices, an analog MTI is obtained as an intermediate frequency output having not only amplitude information but also phase information as an output signal.
Consists of.

Sum (Σ) signal with clutter suppressed, difference (Δ)
The signal is subjected to target detection and tracking processing in the signal processing circuit 15, and the sum (Σ) signal is also sent to the display circuit 16, where it is used to display target information.

Of the target detection processing in the signal processing circuit 15,
The altitude data detection process will be explained using FIG. 5.

In Fig. 5, 17 is a phase detector (PSD);
8 is a discriminator/elevation angle calculation circuit, 19 is a target distance detection circuit, 20 is an altitude calculation circuit, and 24 is a data storage circuit.

The sum (Σ) signal and the difference (Δ) signal are sent to the signal processing circuit 15, and the phase detector (PSD) in the same circuit
17 generates an error output normalized by a sum (Σ) signal, and a discriminator/elevation angle calculation circuit 18 first compares the error output with a reference level to determine the deviation and elevation angle from the beam center elevation angle. The difference (Δφ) is calculated, and then, among the beam center elevation angle values corresponding to each beam stored in the data storage circuit 24, the center elevation angle value (φo) of the beam is calculated as the radar mode value from the reference signal generation circuit 8. It is read in synchronization with the parameter (beam number), and the discriminator/elevation angle calculation circuit 18 calculates the target elevation angle = φ = φo + Δφ. Using the target distance (R) detected by the target distance detection circuit 19 in response to the range clock, the altitude calculation circuit 20 calculates H=g(φ, R, Ho), where H: target altitude g: function φ :Target elevation angle R:Target distance Ho:The target altitude (H) is obtained using the radar installation altitude formula.

As is clear from the above, by approaching the deviation/elevation angle difference (Δφ) to zero through a closed loop, the beam center elevation angle can be adjusted to the target elevation angle (φ).
Unlike a normal tracking radar that tracks the target angle, the radar system that is the object of this invention is an open-loop system, and the beam center elevation angle can be set to the target elevation angle value by sequentially electronically scanning only predetermined elevation angle values. (φ) is calculated as the sum of the center elevation angle (φo) and the deviation elevation angle difference (Δφ) of the detection beam, and is calculated using the off-axis monopulse method (off
-axis Monopulse), and is a method suitable for surveillance radar for simultaneous detection of multiple targets.

The above explanation was about the step of forming and detecting a monopulse antenna pattern in a predetermined direction, but the antenna beam elevation angle direction is changed sequentially (#1) by time division as shown in FIG.
~#n) to obtain the required elevation angle range (EL _nio φ
ELmax) to be covered by electronic scanning.

In the radar device described above, (1) the intermediate frequency is not limited to two stages, but may be selected as appropriate, such as one stage or three stages, as necessary; and (2) in FIG. The antenna beam is formed sequentially from a low elevation angle to a high elevation angle, but there are various scanning methods, such as scanning from a high elevation angle to a low elevation angle, scanning in a special sequence, etc. However, there is no essential difference in the radar device that is the object of the present invention.
Both cases are included in the scope of the present invention.

Conventional off-axis Monopulse electronic scanning array
Since the radar is configured as described above, (1) An analog phase detector (PSD) is used to detect the monopulse error output, but there is a dependence on the sum (Σ) signal level. , (2) The discriminator covers the entire transmit frequency range,
It is difficult to maintain high accuracy over the entire elevation angle range, making high-precision height measurement difficult.

This invention has been made in order to eliminate the drawbacks of the conventional devices as described above.

According to one embodiment of the present invention, (1) Digital MTI is adopted as the moving target detection circuit, and the error output (difference (Δ) signal/sum (Σ) signal) is converted into (i) amplitude information | difference ( Δ) Signal | / | Sum (Σ)
Digital division of signal | (ii) Sign information (phase data of difference (Δ) signal)
− (Phase data of sum (Σ) signal) is decomposed into sign judgment and digitally processed based on digital subtraction of (phase data of sum (Σ) signal) to improve accuracy. ), in order to perform the conversion to calculate the deviation/elevation angle difference (Δφ) with high precision, the data storage circuit 24 of the signal processing circuit 15 stores accurate error characteristics for each beam or each beam/transmission frequency = monopulse characteristic value. (Conversion linear gradient) and beam center elevation angle value are stored as data (constants), and (3) when detecting the target signal, the error output obtained in (1) and (2)
From the data stored in , the deflection elevation angle value (Δφ) and the target elevation angle (φ) are calculated with precision from the conversion linear slope and beam center elevation angle value read out corresponding to the beam number and the transmission frequency. The present invention provides a device that performs digital calculations well.

Hereinafter, one embodiment of the present invention will be described with reference to the drawings. Figure 3 is an explanatory diagram explaining the formula for calculating the target elevation angle using the beam center elevation angle, error output, and conversion linear gradient. Figure 4 is an explanatory diagram that explains the formula for calculating the target elevation angle using the beam center elevation angle, error output, and conversion linear gradient. FIG. 3 is a conceptual diagram showing a state in which n monopulse patterns correspond to different conversion linear gradients.

FIG. 6 is a block diagram showing the main components of the apparatus according to an embodiment of the present invention, out of the structure shown in FIG.

In FIG. 6, reference numerals 21a and 21b are moving target detection circuits, which are composed of a digital MTI instead of the conventional analog MTI. Further, the signal processing circuit 15
It consists of a phase subtraction circuit 22, an elevation calculation circuit 23, a target distance detection circuit 19, an altitude calculation circuit 20, and a data storage circuit 24.

Moving target detection circuit (DMTI) 21 shown in FIG.
a and 21b are general digital MTIs,
Each input signal is divided into in-phase (In-Phase) and quadrature-phase (Quadrature-Phase) and each phase video is output.
After MTI processing, it is recombined and output as [amplitude information] and [phase information].

That is, the sum (Σ) signal of the inputs of the moving target detection circuit 21a is expressed as Σ=|Σ|e ^j( 〓 ^t+ 〓 ⁾ , and is divided into in-phase (I system) and quadrature phase (Q system), respectively. Amplitude information |Σ| and phase information 〓 are obtained through a phase detector, cancellation circuit, and amplitude or phase calculation circuit (not shown), and a difference (△) signal of the input of the moving target detection circuit 21b is also obtained △=|△|e ^j It is expressed as ⁽ 〓 ^t+ △ ⁾ , and similarly amplitude information |△| and phase information 〓 can be obtained.

Here, FIG. 7 shows the moving target detection circuits 21a, 2.
Let the reference signal (e ^j 〓 ^t ) input to 1b be the I system,
It is a vector coordinate plan view of the Q system in which this reference signal is phase-advanced by 90 degrees.

In Figure 7, the sum (Σ) signal and the difference (△) signal are expressed as vectors, where 〓 is the phase difference of the sum (Σ) signal with respect to the reference signal, and 〓 is the phase difference of the difference (△) signal with respect to the reference signal. and is the sum (Σ)
It is the phase difference between the signal and the difference (Δ) signal, and has a polarity of -90° to +90° vertically with respect to the front direction of the antenna.

Σ _I , Σ _Q , Δ _I , and Δ _Q here are vector quantities, and ω=2πf (f: intermediate frequency).

Therefore, for the sum (Σ) signal, (i) Amplitude information: |Σ|=√ ² _I + ² _Q (ii) Phase information: 〓=tan ^-1 (Σ _Q /Σ _I ) Here Σ _I : Σ amplitude of I system Σ _Q : Σ amplitude of Q system Similarly, for the difference (Δ) signal, (i) Amplitude information: |Δ|=√ ² _I + ² _Q (ii) Phase information: = tan ^-1 (Δ _Q /Δ _I ) where Δ _I : Δ amplitude of I system Δ _Q : Δ amplitude of Q system.

From this, △／Σ＝｜△｜／｜Σ｜e ^j( △ ^- 〓 ⁾ ＝
｜△｜/｜Σ｜ ε ^j , and the phase difference between the sum (Σ) signal and the difference (△) signal is given by △−〓, and the sign of this is determined between −90 and 90°. .

In the signal processing circuit 15, the phase subtraction circuit 22 first performs the calculation =〓-〓, and performs the polarity determination of ≧0...S(Δ/Σ)=+ <0...S(Δ/Σ)=-. , FIG. 3b, upper and lower judgments of the monopulse error characteristics are made.

Next, |Δ|/|Σ|=Δ ₁ /Σ ₁ is calculated, and from the monopulse error characteristic slope (=tanη) of the beam number at the transmission frequency read from the data storage circuit 24, the beam Since the deviation elevation angle difference (△φ) from the center elevation angle value (φo) is expressed as (△ output of target signal / Σ output of target signal) / tanη, that is, △φ = (△ ₁ /Σ ₁ ) / tanη Based on the sign determination (S(Δ/Σ)), +Δφor−Δφ is determined.

From the thus obtained Δφ and the beam center elevation angle value (φo), (φ=φo+Δφ) or (φ=φo−Δφ) is calculated.

In this way, the elevation calculation circuit 23 calculates the target elevation angle as follows: target elevation angle=φ ₀ +(Δ output of the target signal/Σ output of the target signal)/tanη, and this is sent to the altitude calculation circuit 20.

In the altitude calculation circuit 20, this elevation angle value and
Target distance (R) detected by target distance detection circuit 19
Calculate the target altitude (H) using the following formula.

H=g(φ, R, Ho) The data storage circuit 24 has the following information as shown in FIG. 4: f (transmission frequency)=fi, i=1, 2,..., k beam number=j, j=1, 2,...,n, store all combinations of tanη=tanη _ji .

The following explanation uses a phased scanning array radar device that scans one beam in the vertical plane as an example.
It is clear that the present invention can be applied to electronically scanned array radars in general, such as frequency scanned array radars, phase/frequency composite array radars, etc. in terms of multi-beam scanning and systems.

As described above, according to the present invention, in order to perform off-axis monopulse angle measurement processing in an electronically scanned monopulse array radar that performs beam scanning electronically in a vertical plane, The moving target detection circuit is a digital MTI, and the height measurement processing circuit in the signal processing circuit is a radar memory that stores monopulse error characteristics (conversion linear slope) corresponding to all beams with elevation angle coverage in all transmission frequency bands and the elevation angle of the beam center. The circuit consists of an elevation calculation circuit and a phase subtraction circuit that perform amplitude information and sign determination of the sum (Σ) signal/difference (Δ) signal (difference (Δ) signal/sum (Σ) signal). This has the effect of realizing high-precision elevation angle measurement (therefore, high-precision height measurement) over the entire transmission frequency band.

[Brief explanation of drawings]

Fig. 1 is a functional diagram showing an example of the configuration of a conventional vertical plane single-beam electronically scanned monopulse array radar, and Fig. 2 is a conceptual diagram showing vertical plane beam scanning in the configuration of Fig. 1. , FIG. 3 is an explanatory diagram showing the principle of target elevation angle calculation in the present invention, FIG. 4 is a conceptual diagram showing the beam arrangement within the entire elevation angle coverage area and monopulse error characteristics at f (transmission frequency) = fi, and FIG. 7 is a functional diagram showing an example of the configuration of the signal processing circuit in FIG. 1; FIG. 6 is a functional diagram showing an example of the configuration of the signal processing circuit according to an embodiment of the present invention The figure is a vector plan view of a sum (Σ) signal and a difference (Δ) signal for explaining an embodiment of the present invention. 1a...first array antenna, 1b...second
Array antenna, 2a...first phase shifter group, 2b
...Second phase shifter group, 3a...First distribution circuit, 3b
...Second distribution circuit, 4...Hybrid, 5...
Phase shifter drive circuit, 6... Beam control circuit, 7...
Transmitter, 8... Reference signal generation circuit, 9... Transmission/reception switching device, 10a... High frequency amplification circuit, 10b... High frequency amplification circuit, 11a, 11b... First mixing circuit, 12a, 12b... Second mixing circuit, 13a,
13b...Intermediate frequency amplification circuit, 14a, 14b...
...Moving target detection circuit, 15...Signal processing circuit, 1
6... Display circuit, 17... Phase detector (PSD),
18...discriminator/elevation angle calculation circuit, 1
9... Target distance detection circuit, 20... Altitude calculation circuit, 21a, 21b... Moving target detection circuit (DMTI), 22... Phase subtraction circuit, 23... Elevation angle calculation circuit, 24... Data storage circuit. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims] 1. It has a plurality of array antennas, and this array antenna is an electronically scanned monopulse array antenna that generates a monopulse pattern in a vertical plane,
In a radar device adapted to measure the altitude of a target, means for generating a sum signal and a difference signal of reception inputs from the plurality of array antennas, and suppressing unnecessary signals from the sum signal and difference signal, respectively. At the same time, a digital moving target detection circuit outputs amplitude information and phase information for each of the sum signal and difference signal, and phase information of the sum signal and difference signal from this digital moving target detection circuit is input,
A phase subtraction circuit that performs polarity determination by subtracting these phase information; a data storage circuit that stores monopulse error characteristics and beam center elevation angle values corresponding to the scanning beam; an elevation calculation circuit that receives the monopulse error characteristic and the beam center elevation angle value as input, and calculates a deviation elevation angle difference from the beam center elevation angle value based on the output of the phase subtraction circuit to calculate a target elevation angle value; , and an altitude calculation circuit that calculates a target altitude from the output of the elevation calculation circuit and the target distance.