JP2630568B2 - Radar equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radar apparatus in which a beam width is equivalently narrowed to obtain a high resolution.

[0002]

2. Description of the Related Art Generally, in a radar apparatus, transmission and reception are performed by a single antenna via a transmission / reception switching unit, and the resolution in the azimuth direction is determined by the radio wave radiated from the antenna toward an observation target. Regarding the beam width, a narrow beam width is required to obtain a high resolution (ability to identify small objects). It is well known that a large aperture antenna is required to form a narrow beam width. However, there is a limit to the size of an antenna used as a part of a radar system, not only to be mounted on a flying object such as a spacecraft but also to be installed on the ground.
There is also a limit on the transmission frequency from the viewpoint of the properties of the object (object) to be observed and the effective use of the frequency. Due to such restrictions, the beam width of the antenna is generally equal to these two.
Since it is determined by two parameters, the degree of freedom is small and a compromise is made to some extent at present.

[0003]

By the way, especially in a radar device mounted on a spacecraft or the like, it is required that the size of the antenna be as small as possible and that the beam width be reduced to have a high resolution. However, under the above-mentioned restrictions, in order to obtain a high resolution for an object, a large-aperture antenna is inevitably required, so that it is extremely difficult to realize a high resolution.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems in the conventional radar apparatus, and has a radar capable of obtaining a high resolution by substantially narrowing a beam width while using a relatively small antenna. It is intended to provide a device.

[0005]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention relates to a radar apparatus mounted on the ground or mounted on a flying object such as a spacecraft, and provided with a phased array antenna as a transmitting / receiving antenna. By adjusting the feeding phase for each antenna element, the beam axis directions of the transmission beam at the time of transmission and the reception beam at the time of reception are different, and only a part of the beam pattern at the time of transmission and the beam pattern at the time of reception in the observation target area Are overlapped with each other so as to form an equivalently narrow beam width.

[0006] Thus, using the phased Les antennae as transmission and reception shared antenna, by adjusting the feeding phase, the transmit beam and with different beam axis direction of the reception beam, the receive beam pattern and the transmit beam pattern in the observation target region By configuring such that only a part overlaps with each other, only the reflected beam of the transmission beam irradiated to the overlapping narrow area is received as the reception beam, and therefore, the radio wave is irradiated by the antenna having a substantially narrow beam width. The same effect can be obtained. In this case,
The power loss increases, but this can be easily dealt with by increasing the transmission power.

[0007]

Next, an embodiment will be described. FIG. 1 is a conceptual diagram of an embodiment in which a radar apparatus according to the present invention is applied to a lunar underground exploration radar system mounted on a lunar orbiting satellite.
Is a schematic view of the embodiment shown in FIG. 1 as viewed from the lateral direction, and FIG. 3 is a schematic view of the embodiment shown in FIG. In the figure, reference numeral 1 denotes a lunar orbiting satellite,
It orbits the moon at an altitude of 70-100 km above,
The satellite 1 is equipped with a radar device 5 including a transmission / reception device 3, a phased array antenna 4, and the like. Reference numeral 6 denotes a transmission beam formed by adjusting a feeding phase to each antenna element in the phased array antenna 4, and reference numeral 7 denotes a reception beam similarly formed at a time shifted from the transmission beam 6. Reference numerals 8 and 9 denote beam axes of the transmission beam 6 and the reception beam 7, respectively. The beam axes 8 and 9 are offset angles θ _t and θ with respect to a vertical axis 10 with respect to the lunar surface 2, respectively.
_{At r} , the phase of each antenna element of the phased array antenna is adjusted such that the beam pattern deviates in the opposite direction from the vertical axis and a part of each beam pattern overlaps on the lunar surface 2. In FIG. 1, 2-1 to 2-2 and 2-3
Indicates the first surface, the second surface, and the third surface of the lunar surface 2, and the arrow attached to the satellite 1 indicates the traveling direction of the satellite 1.

When the transmission beam 6 is radiated from the phased array antenna 4 of the radar apparatus 5 having the above-described configuration toward the moon 2 with a beam width β as shown in FIG. The circular area 11 shown in FIG. 3 is irradiated with the transmission beam. On the other hand, the beam width of the reception beam 7 formed at a time offset by the phased array antenna 4 is also β, and the region 12 of the moon 2 on the basis of the reception beam pattern depends on the beam pattern of the transmission beam 6. This is an area having an overlapping portion 13 that partially overlaps with the area 11.

Thus, the phased array antenna 4
Is configured so that only a part of the transmission beam pattern and the reception beam pattern overlap with each other on the lunar surface 2 that is the observation target area, so that the reception beam 7 receives only the reflected beam from the overlap portion 13. Therefore, the phased array antenna 4 is equivalent to forming the combined transmission / reception beam 15 having a narrow equivalent beam width ω corresponding to the overlapping portion of the transmission beam pattern and the reception beam pattern, and the resolution can be improved. It becomes possible.

In this embodiment, the transmission beam width and the reception beam width β are set to 16 degrees, and each beam axis is shifted by about 6 degrees in the opposite direction with respect to the vertical axis, so that the equivalent beam width ω becomes about 4 degrees. can do. FIG. 4 shows a transmission beam when transmitting from a single phased array antenna with a beam width β = 16 ° and an offset angle θ _t = 6 °, and a transmitting beam when transmitting with a beam width β = 16 ° and an offset angle θ _r = 6 °. FIG. 8 is a diagram showing a calculation example of each beam pattern in the case where the reception beams are formed and the respective beams are superimposed to form a combined beam having an equivalent beam width of ω = 3.8 °; The reception beam pattern, c, indicates a combined beam pattern.

Further, in the radar device of the above embodiment, it is possible to measure the thickness of the topsoil on the moon surface and high resolution. That is, in order to measure the thickness of the lunar top soil, the transmitted beam 6 formed by the phased array antenna 4 is reflected from the first surface 2-1 of the lunar surface 2 to return, It must be physically distinguishable at the receiver from the reflected beam returning from surface 2-2. In the above embodiment, the transmission beam pattern and the reception beam pattern are partially overlapped to form a combined transmission / reception beam 15 having a narrow equivalent beam width ω. In the following description, it is assumed that the combined transmission / reception beam 15 is formed from the phased array antenna 4. In FIG. After the reflected beam from one intersection A with the first surface 2-1 has reached the receiver, the intersection of the perpendicular dropped from the phased array antenna 4 to the moon 2 and the second surface 2-2 The reflected beam from B (the shortest part between the phased array antenna 4 and the second surface 2-2) must reach so as to distinguish between the two.

Since the power of the reflected beam from point A on the first surface 2-1 of the lunar surface 2 is much larger than the power of the reflected beam from point B on the second surface 2-2, points A and B In order to clearly distinguish a reflected beam from a point, it is understood that if the pulse width is ignored and the position of the phased array antenna is O, the following equation (1) should be satisfied: OA length <OB length ... (1)

If the above equation (1) is satisfied, it is possible to measure the thickness HB (depth resolution) of the first layer. However, in order to improve the depth resolution, the length of the OA is required. , Ie, the length of AH should be shortened.
Note that point H is the intersection of the perpendicular drawn from the phased array antenna 4 to the moon surface 2 and the first surface 2-1. In order to shorten the length of the AH, a large aperture antenna which generally forms a very narrow beam width is required. In the present invention, however, a single phased array antenna 4 is used as described above. , The length of AH can be shortened, the length of OA can be shortened, and therefore the distance of short HB can be measured. Resolution can be improved.

Considering the pulse width τ (s), the equation (1) is expressed as the following equation (2). OA length <OB length−cτ / 2 (2) where c is the speed of light. As can be seen from equation (2), in order to increase the depth resolution, it is necessary not only to narrow the beam width but also to shorten the pulse width τ. In conventional ordinary radar, the azimuth resolution determined by the beam width and the distance resolution determined by the pulse width are independent,
In the radar apparatus according to the present invention, the depth resolution corresponding to the distance resolution is represented by the minimum value of BH satisfying the condition of the above equation (2), and the equation (2) involves the term of AH representing the azimuth resolution. Therefore, unlike ordinary radar, it can be seen that depth resolution (distance resolution) is related to azimuth resolution.

In the above embodiment, the present invention is applied to the lunar subsurface exploration radar mounted on the lunar orbiting observation satellite. However, the present invention is not limited to this, and the present invention is not limited to this. it is applicable over a wide range such as radar for the body.

[0016]

As described above with reference to the embodiments,
According to the present invention, since a single phased array antenna is used to form a combined transmission / reception beam having an equivalently narrow beam width, the beam width can be equivalently narrowed with a small antenna. , A spacecraft or the like can be easily mounted.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing one embodiment of a radar apparatus according to the present invention.

FIG. 2 is a schematic view of the embodiment shown in FIG. 1 as viewed from a lateral direction.

FIG. 3 is a diagram showing a spread state of a beam pattern on the moon surface in the embodiment shown in FIG. 1;

FIG. 4 is a diagram showing an example of calculation of each beam pattern of a transmission beam, a reception beam, and a combined transmission / reception beam in the embodiment shown in FIG.

[Explanation of symbols]

 1 moon orbiting satellite 2 lunar surface 3 transmitting and receiving device 4 phased array antenna 5 radar device 6 transmitting beam 7 receiving beam 8 transmitting beam axis 9 receiving beam axis 10 vertical axis 11 transmitting beam pattern area 12 receiving beam pattern area 13 overlapping part 15 synthesis Transmit and receive beam

Claims (1)

(57) [Claims] 1. A radar apparatus for ground installation or mounted on a flying object such as a spacecraft, comprising a phased array antenna as a transmitting / receiving antenna, adjusting a power supply phase for each antenna element and transmitting and receiving a transmission beam and a reception beam at the time of transmission. The direction of each beam axis of the receiving beam at the time is made different, so that only a part of the beam pattern at the time of transmission and the beam pattern at the time of reception overlap with each other in the observation target area, so that an equivalent narrow beam width is formed. A radar device characterized in that: