JPS6276477A - Synthetic aperture radar equipment - Google Patents

Abstract

PURPOSE:To vary the characteristic of an antenna beam pattern and an orienting direction, to make operability flexible, to solidify an artificial satellite transmitter at a high frequency and to utilize the frequency of bands C and X by constituting the antenna of a synthetic opening radar as an active array. CONSTITUTION:A beam controller 11 reads out beam control contents specifying a beam control command out of a built-in ROM, and outputs them as phase data phi1, phi2,...phin in four-bit serial digital code format. Many kinds of phase data necessary for controlling beams are previously stored in the built-in ROM, and the desired set of phase data are read out under the control of a built-in program at every beam control command input. The phase data outputted in such a way is supplied to the phase shifter driver 22 of transmission/reception modules 2-1-2-N. The phase shifter driver 22 converts the phase data phi1 inputted in the four-bit serial data code from serial to parallel and amplifies it up to a necessary level so as to supply it to a variable phase shifter 21.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a synthetic aperture radar device, and particularly to a synthetic aperture radar device with an improved antenna beam control function.

[Conventional technology]

A flying object such as an aircraft or an artificial satellite traveling on a preset flight path emits radar radio waves in a predetermined direction to the ground on the side of the flight direction, and uses the reflected data acquired one after another to detect radar waves on the ground. It is well known for its synthetic aperture radar system, which synthesizes the state into an image similar to a photograph.

In order to visualize radar echoes, it is necessary to have high resolution for both the distance to the target and the azimuth of the target as seen from the flying object. Therefore, the distance direction is usually L F M (L'1near FM) pulses are transmitted, and the received signal is compressed by passing it through a filter whose time vs. frequency characteristics are inverse to that of the transmitted signal, while the azimuth information is transmitted using a beam that takes advantage of the fact that the radar equipment itself is moving at high speed. High resolution is achieved using sharpening technology.

There are two methods for beam sharpening technology: one is to synthesize radar echoes acquired one after another as the radar moves at high speed, and synthesize a large-diameter antenna with equal constraints. The other one is caused by the high speed movement of the radar.
This is a method of dividing the actual radar beam into narrow beams equally parsimoniously by using a filter to subdivide the Doppler frequency in the radar echo. Radar signals in a predetermined directional direction are transmitted and received via a near array, and side A/Y king (side looking) is performed.
.

The desired data is obtained by scanning the ground surface using extreme mapping modes such as squint mode (5 quint mode) and spotlight (spo light).

[Problem that the invention seeks to solve]

The composite radar device has azimuth resolution, scanning width, directivity angle (off-nadir angle), 8/N (Signal/No.1se
) are related to each other in such a way that they constrain each other, and this becomes a constraint in system design, limiting the range of selection of parameters such as scales used in design, and therefore limiting the operating conditions. be. The above-mentioned scanning width is the scanning width of the ground surface by the synthetic aperture radar, and the pointing angle is the off-nadir (off-nadir), which is the distance between the vertical ridge drawn from the flying object to the ground surface and the beam direction center direction.
) is a corner.

First, let's consider the above-mentioned problem, taking azimuth resolution as an example. The azimuth resolution depends on the antenna aperture length in the azimuth direction perpendicular to the direction of travel, that is, the beam l. Therefore, in order to increase the resolution, the aperture length must be made smaller and the beam width must be made wider. However, increasing the beam width in the direction of expansion in this way inevitably contradicts the condition of reducing ambiguity, so there are limitations, and for the same reason, the scanning width should also be as wide as possible. This should be smaller (
scan #A Buddha's hope '4c fundamentally limits.

Furthermore, although synthetic aperture radar uses pulse compression technology, it still requires considerable peak power to achieve the desired S/Ni, which necessitates an increase in shape and size. Payload (payloa)
d) For artificial satellites with restrictions, solid-state transmitters are limited to the L-band, and C-band,
Unable to acquire data on band.

Furthermore, the antenna directivity angle has an optimal value depending on the observation target, and is also related to other parameters, so it is fixed at a fixed value.
There are various problems, such as not being able to suit all observation targets with a single antenna directivity angle.

An object of the present invention is to eliminate the above-mentioned drawbacks, and to configure the antenna of a synthetic aperture radar as a so-called active array, thereby making the characteristics of the antenna beam pattern and directivity variable, thereby making the operability extremely flexible. Even at high frequencies, it is possible to make solid-state transmitters for artificial satellites, and the C-band and X-band frequencies can be used, and the late #r
It is an object of the present invention to provide a combined amount Rorader device that also has high function retention for C.

[Means for solving problems]

In the synthetic aperture radar yC of the present invention, an array antenna in which a number of radiating elements are arranged regularly or a plurality of radiation concentrators klllfL is used as an element in an array antenna with a group of unit elements arranged regularly. It is configured to include antenna beam control means that can change the pattern characteristics and directivity direction of the antenna beam by controlling the relative phase between excitation signals applied to each antenna or unit antenna.

〔Example〕

Next, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.

The configuration of the one-scent embodiment shown in FIG. 1 is as follows:
1-N, transmitting/receiving modules 2-1 to -2-N1 distribution/synthesizer 3. T/几SWITCH 4. Transmission exciter 5, 8TAL
O(8TAble Local Osc-111a
tor) 6, synchronization signal generator 7. Transmitter 8° synchronous detector 9. Signal processing device 10. and a beam controller 11, and transmitting/receiving modules 2-1 to 2-H.
Each of the variable groups trFiya21.

Phase shifter driver 22, T/几 switch 23. % force width gauge 24. Serculator 25. Limiter 'L'/l
(It is configured with an l switch 26, a T/R switch controller 27, a low noise amplifier 28, etc.).

Each of the antenna elements 1-1 to 1-N is a single radiating element 1, and has an aspect set in advance.
A planar array is arranged in a plane with a ratio of
er array ).

Further, these antenna elements are utilized as a so-called active array having an integrated structure with the transmitting/receiving modules 2-1 to 2-N each having an IC configuration.

The entire system performs synchronous operation using a timing synchronization signal generated by a synchronization signal generator 7.

The synchronization signal generator 7 is supplied with a high frequency reference signal to be used as a time reference from the 5TALO 6, and the transmission exciter 5 is supplied with a transmission synchronization signal for setting the timing of the transmission pulse repetition period, and the transmission/reception modules 2-1 to 2- The N and T/R switch 4 receives a T/R timing synchronization signal that determines the transmission timing set by the transmission synchronization signal and the reception timing set corresponding to this transmission timing and the transmission range, etc. A beam control clock signal as time information synchronized with the transmission/reception timing is supplied to the controller 11 to perform synchronized system operation.

5TALO 6 has a crystal oscillator, a frequency synthesizer, etc., and provides a high frequency reference signal as a time standard to the synchronization signal generator 7, and also transmits this high frequency reference signal to the oscillation exciter 5.
The transmitting exciter 5 uses a pulse modulation circuit to perform predetermined pulse modulation (LFM modulation in this embodiment), and further outputs a transmitting excitation word at a predetermined carrier frequency and level using an up-converter, an excitation amplifier, etc. The signal is output to the T/R switch 4 at a pulse repetition period determined by the transmission synchronization signal.

The T/R switch 4 outputs the transmission excitation word=i T/R
.

The timing synchronization signal is output at the timing and supplied to the distributor/synthesizer 3.

The distributor/synthesizer 3 outputs the transmitted excitation word input in this way into N
It is equally divided and supplied to N transmitting/receiving modules 2-1 to 2-N.

The transmitter/receiver modules 2-1 to 2-N receive the 1 input in this way.
/N level transmission excitation word output, respectively preset phases φ8. ψ, .

The beam controller 11 receives beam control commands from an external source such as a flying object or a ground control center. This beam control command is a command that specifies the beam characteristics and directivity of the synthetic aperture radar beam to be synthesized by a radar mounted on a platform such as an aircraft or an artificial satellite. Phase information to be given to each antenna element is determined in order to obtain desired characteristics and direction of transmission beam pattern by the formed planar array. In this example, in this way,
Although the transmission beam control information is specified from the outside, it may of course be generated within the beam controller 11. Further, although it is assumed that the beam control clock signal of the beam controller 11 is also supplied from the synchronization signal generator 7, it may be generated internally in the beam controller 11.

Now, the beam controller 11 stores the beam control contents specified by the beam control command in a built-in ROM (ReadOnly M
emoly) and converts it into 4-bit serial digital code format phase data ψ1. ψ7. ...Output as ψ. Inside, i? : A set of phase data for the model required for beam control is stored in the ROM in advance, and a desired set of phase data is read out under the control of a built-in program each time a beam control command is input.

The phase data output in this way is transmitted to the transmitter/receiver module 2-1.
~2-N phase shifter drivers 22. Taking the transmitting/receiving module 2-1 as an example, phase data ψ1
is supplied to the phase shifter driver 22.

The phase shifter driver 22 performs serial/parallel conversion of phase data ψ input as a 4-bit serial digital code, amplifies it to a required level, and supplies the data to the variable phase shifter 21 .

The variable phase shifter 21 uses a phase modulator switch using a PIN diode, etc., and performs phase control corresponding to the phase data ψ on 1/H of the transmitting exciter output input from the distributor/synthesizer 3.

The output whose phase has been controlled by the variable phase shifter 21 is outputted by a T/R switch 23 under the control of a T/R switch controller 27 while receiving a T/R switch control signal synchronized with a timing synchronization signal. The signal is inputted to the power amplifier 24 at the timing of the transmission pulse repetition period, subjected to necessary level amplification, and applied to the antenna element 1-1 via the circulator 25, where it is radiated. The distributed output of the distributor/synthesizer 3, which has undergone phase control corresponding to the phase data ψ2 to ψ, is applied to the antenna elements 1-2 to 1-H in exactly the same manner by the transmitter/receiver modules 2-2 to 2-N. radiated as radio waves.

In this way, the antenna element 1-
The radio waves radiated from each of 1 to 1-N are spatially combined, and a transmission beam with desired pattern characteristics and directional direction is radiated from the radar device mounted on the platform.

Now, the reflected signals from the transmission beams thus radiated to the ground are received by the antenna elements 1-1 to 1-N, and are received by the circulators 25. The signal is input to a low noise amplifier 28 via a limiter/T/R switch 26.

The limiter/'I'/R switch 26 functions as a limiter as a protection circuit for the transmission output, and a T/R switch that switches between transmission and reception.
R switch, and T/R switch 23 and T/R switch 23.
Under the control of the R switch 27, it is turned off during the transmission period and turned on during the reception period to switch the input of the received signal. On the other hand, the T/R S'Pt 23 turns on the signal path from the variable phase shifter 21 to the power amplifier 24 during the transmission period, and connects the output of the low noise amplifier 28 to the variable phase shifter 24 during the reception period, as described above. 21. The T/R switch controller 27 receives the T/R timing synchronization signal from the synchronization signal generator 7 and controls the limiter/TR switch 27 and the T/R switch 23 to perform the above-mentioned switching operation. Generates switch control signals.

The received signal amplified by the low noise amplifier 28 is subjected to phase shift control via the T/R switch 23 and is supplied to the combiner of the distributor/combiner 3. In this way, the phase shifter v used during reception processing
IJ is performed for the purpose of making the transmitting and receiving antenna pattern characteristics and directivity the same, and the output of the low noise amplifier 28 input via the T/R switch 23 is the same phase data ψ as at the time of transmission.

corresponds to and undergoes a phase shift. Transmission/reception module 2-2~
The received signal at 2-NK is similarly phase-shifted using phase data ψ, ~ψ, to match the transmitting and receiving antenna pattern characteristics and directivity direction.

The beam controller 11 receives a beam control clock signal synchronized with the timing of transmission and reception, and generates phase data ψ8.8 for beam control during transmission and reception. ψ2゜・・・・・・ψ
We will provide the following.

Transmission/reception module 2-1 supplied to distributor/synthesizer 3
, 2-2, . . . 2-N are subjected to directional synthesis and addition in a combiner, and are supplied to 8 after reception via a T/R switch 4.

After reception, the reception output amplified to a predetermined level in 8 is synchronously detected by a synchronous detector 9 through multiplication processing with a high frequency reference signal supplied from 8 TALO 6, and then sent to a signal processing section 10.
provided to.

The signal processing device 10 is a known synthetic aperture radar image processing device, and performs compression processing of two-dimensional data of a target spread in the distance and azimuth directions inputted from the synchronous detector 2, that is, range compression, azimuth compression, and corner turning. A desired video signal is extracted through processing and techniques such as multiplexing and reprocessing.

The basic feature of the present invention is that the antenna beam pattern and directional characteristics of a synthetic aperture radar are made variable, and modifications of the embodiment shown in FIG. 1 are also conceivable.

For example, in this embodiment, the phase data ψ1 for beam control
．． ψ2. Although each ψNld is supplied to the transmitter/receiver module as 4-bit serial data, it is obvious that it would be easy to provide this as parallel data format. Furthermore, in this embodiment, this phase data is supplied to each transmitting/receiving module in parallel.
A different tag is attached to each of the ψ, and the data is serially supplied to each transmitting/receiving module as serial data, and each transmitting/receiving module uses a decoder to decode the contents specified by the tag and extracts its own transmitting/receiving module. It's okay.

Furthermore, in this example, each antenna element uses a single radiating element, but it is clear that the implementation can be carried out in almost the same way even if this is replaced with a unit element group consisting of a combination of multiple radiating elements. All of these can be easily implemented without detracting from the spirit of the invention.

〔Effect of the invention〕

As explained above, according to the present invention, by providing a synthetic aperture radar device equipped with means that can vary the beam pattern characteristics and pointing direction of the antenna, it is possible to achieve wide coverage, low resolution or narrow coverage depending on the operational purpose. In addition to being able to arbitrarily select one of the high-resolution operating modes and setting the antenna beam to the optimal state depending on the operational purpose, the transmission power that needs to be applied to each individual antenna element can be reduced even at high output. Therefore, it is easy to integrate high-power synthetic aperture radar transmitters in high frequency bands such as the C band and The present invention has the effect that a synthetic aperture radar device can be realized which can achieve high reliability without affecting the performance of the system, and can reduce the requirement for a redundant system in the system.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention. 1-1~l-N...Antenna element, 2-1~2
-N...Transmission/reception module, 3...Synthesizer/synthesizer, 4...T/R switch, 5...
...Transmission exciter, 6...5TAL0,7...
・Synchronization signal generator, 8...Receiver, 9...
... Synchronous detector, 10 ... Signal processor, beam controller 11.21 ... Variable phase shifter, 22 ...
... Phase shifter driver, 23 ... T/L switch, 24 ... Power amplifier, 25 ... Circulator, 26 ... Limiter T/ R switch, 27...T/R switch controller, 28...
...Low noise amplifier. 7・′−′−＼

Claims (1)

[Claims] In synthetic aperture radar, an array antenna in which multiple radiating elements are regularly arranged
Or, in an array antenna using a group of unit elements in which multiple radiating elements are regularly arranged as a unit, the pattern characteristics and directivity of the antenna beam can be controlled by controlling the relative phase between the excitation signals applied to each element antenna or unit antenna. A synthetic aperture radar device comprising antenna beam control means that can change direction.